错误：对象引用未设置为对象的实例。 [英] Error: Object reference not set to an instance of an object.

查看：88 发布时间：2019/6/13 23:12:55 C# SQL-Server

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问题描述

我是第一次发帖问题所以如果我不遵循任何主题或任何错误请原谅我...

我收到此错误我的代码：

对象引用未设置为对象的实例。

这是我的代码：

  void  document_PrintPage（ object  sender，PrintPageEventArgs e）
 {
 
 e.Graphics.DrawImage（_memoryImage， 0 ， 0 ）; 
 
} 
  private 位图_memoryImage; 
 
  private   void  CaptureScreen（）
 {
  //  使用构造因为图形对象不 
  //  在离开方法范围时自动处理 
 使用（  var  myGraphics = CreateGraphics（））
 {
  var  s = Size; 
 _memoryImage =  new 位图（ 1500 ， 1000 ，myGraphics）; 
 使用（ var  memoryGraphics = Graphics.FromImage（_memoryImage））
 {
 printDocument2.DefaultPageSettings.PaperSize =  new  System.Drawing.Printing.PaperSize（  PaperA4， 826 ， 1169 ）; 
 memoryGraphics.CopyFromScreen（Location.X，Location.Y， 70 ， 30 ，s） ; 
} 
} 
} 
 
  private   void  printDocument2_PrintPage（ object  sender，PrintPageEventArgs e）
 {
  //  计算考虑页边距的宽度和高度缩放 
  var  wScale = e.MarginBounds.Width /（ float ）_ memoryImage.Width; 
  var  hScale = e.MarginBounds.Height /（ float ）_ memoryImage.Height; 
 
  //  选择两个比例中较小的一个 
 < span class =code-keyword> var  scale = wScale <  hScale？ wScale：hScale; 
 
  //  对图像应用缩放 
 e.Graphics .ScaleTransform（规模，比例）; 
 
  //  打印到默认打印机的页面 
 e.Graphics .DrawImage（_memoryImage， 70 ， 30 ）; 
 printDocument2.DefaultPageSettings.PaperSize =  new  System.Drawing.Printing.PaperSize（  PaperA4， 826 ， 1169 ）; 
} 
 私有  void  btnprintpre_Click（ object  sender，EventArgs e）
 {
  //  将PrintPreviewDialog与PrintDocument相关联。 
 printPreviewDialog1.Document = printDocument2; 
 
  //  显示PrintPreview对话框 
  //   printPreviewDialog1.ShowDialog（）;  
 
 printPreviewDialog1.WindowState = FormWindowState.Maximized; 
 printPreviewDialog1.ShowDialog（）; 
}

我接近var wScale = e.MarginBounds.Width /（float）_memoryImage.Width ;

因此，如果有人遇到此错误或可以解决我的问题，请帮助我。

解决方案

< blockquote> e.MarginBounds.Width或（float）_memoryImage.Width返回null给你错误原因的语句

调试你的代码并检查_memoryImage变量是否被分配了一些值。

在使用其属性之前检查对象值是一个很好的做法。

喜欢

if（_memoryImage！= null）

{

//在这里写下您的全部代码

}

< solve>

我的问题通过将正常按钮更改为菜单按钮并将代码放入其中来解决，但我现在面临另一个错误，

这是我的完整代码：

 使用系统; 
 使用 System.Collections.Generic; 
 使用 System.ComponentModel; 
 使用 System.Data; 
 使用 System.Drawing; 
 使用 System.Linq; 
 使用 System.Text; 
 使用 System.Windows.Forms; 
 使用 System.Data.SqlClient; 
 使用 System.Diagnostics; 
 使用 System.Drawing.Printing; 
 使用 System.Data.SqlTypes; 
 使用 Microsoft.SqlServer.Server; 
 使用 System.Timers; 
 
 命名空间 ComplaintReport 
 {
  public   partial   class  MRU240：表格
 {
 
  private  PrintPreviewDialog Pv; 
  private  PageSetupDialog Ps; 
  private  PrintDocument Pd; 
  private  PrintDialog Pr; 
 
  private  System.Windows.Forms.MainMenu mainMenu1; 
  private  System.Windows.Forms.MenuItem mnuFile; 
  private  System.Windows.Forms.MenuItem mnuSetup; 
  private  System.Windows.Forms.MenuItem mnuPreview; 
  private  System.Windows.Forms.MenuItem mnuPrint; 
  private  System.Windows.Forms.Button cmdQuit; 
 
  public  MRU240（）
 {
 InitializeComponent（）; 
 
 Pv =  new  PrintPreviewDialog（）; 
 Ps =  new  PageSetupDialog（）; 
 Pr =  new  PrintDialog（）; 
 Pd =  new  PrintDocument（）; 
 
 Pd.DocumentName =  我的新文件; 
 Pv.Document = Pd; 
 Ps.Document = Pd; 
 Pr.Document = Pd; 
} 
 
 
 
  private   void  clearAll（）
 {
 txt1.Text =  ; 
 txtsno.Text =  ; 
 txt3.Text =  ; 
 txt4.Text =  ; 
 txt5.Text =  ; 
 txt6.Text =  ; 
 txt7.Text =  ; 
 txt8.Text =  ; 
 txt9.Text =  ; 
 txt11.Text =  ; 
 txt12.Text =  ; 
 txt13.Text =  ; 
 txt14.Text =  ; 
 txt15.Text =  ; 
 txt16.Text =  ; 
 txt17.Text =  ; 
 txt18.Text =  ; 
 txt19.Text =  ; 
 txt20.Text =  ; 
 
} 
  private   void  newToolStripMenuItem_Click（ object  sender，EventArgs e）
 {
 clearAll（）; 
 
 btnedit.Visible =  false ; 
 btnupdate.Visible =  false ; 
 txt1.Visible =  true ; 
 txt2.Visible =  true ; 
 txtsno.Visible =  true ; 
 txt3.Visible =  true ; 
 txt4.Visible =  true ; 
 txt5.Visible =  true ; 
 txt6.Visible =  true ; 
 txt7.Visible =  true ; 
 txt8.Visible =  true ; 
 txt9.Visible =  true ; 
 txt11.Visible =  true ; 
 txt12.Visible =  true ; 
 txt13.Visible =  true ; 
 txt14.Visible =  true ; 
 txt15.Visible =  true ; 
 txt16.Visible =  true ; 
 txt17.Visible =  true ; 
 txt18.Visible =  true ; 
 txt19.Visible =  true ; 
 txt20.Visible =  true ; 
 lbluno.Visible =  false ; 
 label1.Visible =  true ; 
 label2.Visible =  true ; 
 label3.Visible =  true ; 
 label4.Visible =  true ; 
 label5.Visible =  true ; 
 label6.Visible =  true ; 
 label7.Visible =  true ; 
 label8.Visible =  true ; 
 label9.Visible =  true ; 
 label10.Visible =  true ; 
 label11.Visible =  true ; 
 label12.Visible =  true ; 
 label13.Visible =  true ; 
 label14.Visible =  true ; 
 label15.Visible =  true ; 
 label16.Visible =  true ; 
 label17.Visible =  true ; 
 label18.Visible =  true ; 
 label19.Visible =  true ; 
 label21.Visible =  true ; 
 label22.Visible =  true ; 
 label23.Visible =  true ; 
 label25.Visible =  true ; 
 btnexit.Visible =  true ; 
 comboBox1.Visible =  false ; 
 
 txt1.ReadOnly =  false ; 
 txt3.ReadOnly =  false ; 
 txt4.ReadOnly =  false ; 
 txt5.ReadOnly =  false ; 
 txt6.ReadOnly =  false ; 
 txt7.ReadOnly =  false ; 
 txt8.ReadOnly =  false ; 
 txt9.ReadOnly =  false ; 
 txt11.ReadOnly =  false ; 
 txt12.ReadOnly =  false ; 
 txt13.ReadOnly =  false ; 
 txt14.ReadOnly =  false ; 
 txt15.ReadOnly =  false ; 
 txt16.ReadOnly =  false ; 
 txt17.ReadOnly =  false ; 
 txt18.ReadOnly =  false ; 
 txt19.ReadOnly =  false ; 
 txt20.ReadOnly =  false ; 
 txtsno.ReadOnly =  false ; 
 txt2.ReadOnly =  true ; 
} 
 
  private   void  openToolStripMenuItem_Click（ object  sender，EventArgs e）
 {
  string  cs =   Data Source = 192.168.1.133; database = ComplaintReport; user id = sa; password = ssdrnd; 
 SqlConnection conn =  new  SqlConnection（cs）; 
 SqlCommand cmd =  new  SqlCommand（）; 
 conn.Open（）; 
 
 SqlDataAdapter da =  new  SqlDataAdapter（ 从MRU240中选择Mno，conn）; 
 DataSet ds =  new  DataSet（）; 
 cmd =  new  SqlCommand（ 选择Mno来自MRU240，conn）; 
 da.Fill（ds，  mru240）; 
 
 comboBox1.DataSource = ds.Tables [  mru240]; 
 comboBox1.DisplayMember =   Mno; 
 conn.Close（）; 
 
  //   btnprint.Visible = true;  
 
 comboBox1.Visible =  true ; 
 lbluno.Visible =  true ; 
 btnupdate.Visible =  false ; 
 txt1.Visible =  false ; 
 txt2.Visible =  false ; 
 txtsno.Visible =  false ; 
 txt3.Visible =  false ; 
 txt4.Visible =  false ; 
 txt5.Visible =  false ; 
 txt6.Visible =  false ; 
 txt7.Visible =  false ; 
 txt8.Visible =  false ; 
 txt9.Visible =  false ; 
 txt11.Visible =  false ; 
 txt12.Visible =  false ; 
 txt13.Visible =  false ; 
 txt14.Visible =  false ; 
 txt15.Visible =  false ; 
 txt16.Visible =  false ; 
 txt17.Visible =  false ; 
 txt18.Visible =  false ; 
 txt19.Visible =  false ; 
 txt20.Visible =  false ; 
 label3.Visible =  false ; 
 label2.Visible =  false ; 
 label4.Visible =  false ; 
 label5.Visible =  false ; 
 label6.Visible =  false ; 
 label7.Visible =  false ; 
 label8.Visible =  false ; 
 label9.Visible =  false ; 
 label10.Visible =  false ; 
 label11.Visible =  false ; 
 label12.Visible =  false ; 
 label13.Visible =  false ; 
 label14.Visible =  false ; 
 label15.Visible =  false ; 
 label16.Visible =  false ; 
 label17.Visible =  false ; 
 label18.Visible =  false ; 
 label19.Visible =  false ; 
 label21.Visible =  false ; 
 label22.Visible =  false ; 
 label23.Visible =  false ; 
 label25.Visible =  false ; 
 btnedit.Visible =  false ; 
 
 btnexit.Visible =  false ; 
 
} 
 
 
  private   void  toolStripMenuback_Click（ object  sender，EventArgs e）
 {
 SSCVR obj6 =  new  SSCVR（）; 
 obj6.Show（）; 
  this  .Hide（）; 
} 
 
 
 私人  void  MRU240_Load（< span class =code-keyword> object  sender，EventArgs e）
 {
 comboBox1.DropDownHeight = comboBox1.ItemHeight *  10 ; 
 comboBox1.MouseWheel + =  new  MouseEventHandler（comboBox1_MouseWheel）; 
 
 txt1.Visible =  false ; 
 txt2.Visible =  false ; 
 txtsno.Visible =  false ; 
 txt3.Visible =  false ; 
 txt4.Visible =  false ; 
 txt5.Visible =  false ; 
 txt6.Visible =  false ; 
 txt7.Visible =  false ; 
 txt8.Visible =  false ; 
 txt9.Visible =  false ; 
 txt11.Visible =  false ; 
 txt12.Visible =  false ; 
 txt13.Visible =  false ; 
 txt14.Visible =  false ; 
 txt15.Visible =  false ; 
 txt16.Visible =  false ; 
 txt17.Visible =  false ; 
 txt18.Visible =  false ; 
 txt19.Visible =  false ; 
 txt20.Visible =  false ; 
 txtsno.Visible =  false ; 
 comboBox1.Visible =  false ; 
 label2.Visible =  false ; 
 label4.Visible =  false ; 
 label5.Visible =  false ; 
 label6.Visible =  false ; 
 label7.Visible =  false ; 
 label8.Visible =  false ; 
 label9.Visible =  false ; 
 label10.Visible =  false ; 
 label11.Visible =  false ; 
 label12.Visible =  false ; 
 label13.Visible =  false ; 
 label14.Visible =  false ; 
 label15.Visible =  false ; 
 label16.Visible =  false ; 
 label17.Visible =  false ; 
 label18.Visible =  false ; 
 label19.Visible =  false ; 
 label21.Visible =  false ; 
 label22.Visible =  false ; 
 label23.Visible =  false ; 
 label25.Visible =  false ; 
 label13.Visible =  false ; 
 label3.Visible =  false ; 
 btnupdate.Visible =  false ; 
 btnexit.Visible =  false ; 
 
} 
  void  comboBox1_MouseWheel（ object  sender，MouseEventArgs e） 
 {
（（HandledMouseEventArgs）e）。已处理=  true ; 
} 
 
 
 
  private   void  btnexit_Click（ object  sender，EventArgs e）
 {
 SSCVRGSE obj4 =  new  SSCVRGSE（）; 
 obj4.Show（）; 
  this  .Hide（）; 
} 
 
 
 
  private   void  saveToolStripMenuItem_Click（ object  sender，EventArgs e）
 {
  string  cs = < span class =code-string>  Data Source = 192.168.1.133; database = ComplaintReport; user id = sa; password = ssdrnd; 
 SqlConnection conn =  new  SqlConnection（cs）; 
  if （txtsno.Text ==   ）
 {
 MessageBox.Show（ 请输入序列号< /跨度>）; 
 txtsno.Focus（）; 
} 
  if （txtsno.Text.Length >  =  7 ）
 {
 MessageBox.Show（ 序列号低于7个字符）; 
 txtsno.Focus（）; 
} 
 
 
 尝试 
 {
  string  cfd = txt1.Text; 
  string  Uno = txt2.Text; 
  string  Mno = txtsno.Text; 
  string  cprc = txt3.Text; 
  string  sdc = txt4.Text; 
  string  contact = txt5.Text; 
  string  orderno = txt6.Text; 
  string  ino = txt7.Text; 
  string  consig = txt8.Text; 
  string  pft = txt9.Text; 
  string  remarks = txt11.Text; 
  string  obsv = txt12.Text; 
  string  disptach = txt13.Text; 
  string  repair = txt14.Text; 
  string  cause = txt15.Text; 
  string  userinfo = txt16.Text; 
  string  remedial = txt17.Text; 
  string  feedbck = txt18.Text; 
  string  conclu = txt19.Text; 
  string  notes = txt20.Text; 
 
 SqlCommand cmd =  new  SqlCommand（ 插入MRU240值（@ cfd，@ Uno，@ Mno，@ cprc，@ sdc，@ contact，@ orderno，@ ino，@ consig，@ pft，@ remarks，@ obsv，@ dispatch，@ repair， @ cause，@ userinfo，@ remedial，@ feedbck，@ conclu，@ notes），conn）; 
 cmd.Parameters.AddWithValue（  @ cfd，cfd）; 
 cmd.Parameters.AddWithValue（  @ Uno，Uno）; 
 cmd.Parameters.AddWithValue（  @ Mno，Mno）; 
 cmd.Parameters.AddWithValue（  @ cprc，cprc）; 
 cmd.Parameters.AddWithValue（  @ sdc，sdc）; 
 cmd.Parameters.AddWithValue（  @ contact，contact）; 
 cmd.Parameters.AddWithValue（  @ orderno，orderno）; 
 cmd.Parameters.AddWithValue（  @ ino，ino）; 
 cmd.Parameters.AddWithValue（  @ consig，consig）; 
 cmd.Parameters.AddWithValue（  @ pft，pft）; 
 cmd.Parameters.AddWithValue（  @ remarks，备注）; 
 cmd.Parameters.AddWithValue（  @ obsv，obsv）; 
 cmd.Parameters.AddWithValue（  @ dispatch，disptach）; 
 cmd.Parameters.AddWithValue（  @ repair，修复）; 
 cmd.Parameters.AddWithValue（  @ cause，cause）; 
 cmd.Parameters.AddWithValue（  @ userinfo，userinfo）; 
 cmd.Parameters.AddWithValue（  @ remedial，补救）; 
 cmd.Parameters.AddWithValue（  @ feedbck，feedbck）; 
 cmd.Parameters.AddWithValue（  @ conclu，conclu）; 
 cmd.Parameters.AddWithValue（  @ notes，notes）; 
 
 conn.Open（）; 
  int  i = cmd.ExecuteNonQuery（）; 
  if （i ==  1 ）
 {
 MessageBox。显示（ 保存记录）; 
 clearAll（）; 
} 
 
} 
  catch （Exception ex）
 {
 MessageBox.Show（ ex.Message）; 
} 
 conn.Close（）; 
 
} 
 
  private   void  btnedit_Click_1（< span class =code-keyword> object  sender，EventArgs e）
 {
 txt1.ReadOnly =  false ; 
 lbluno.Visible =  true ; 
 txt3.ReadOnly =  false ; 
 txt4.ReadOnly =  false ; 
 txt5.ReadOnly =  false ; 
 txt6.ReadOnly =  false ; 
 txt7.ReadOnly =  false ; 
 txt8.ReadOnly =  false ; 
 txt9.ReadOnly =  false ; 
 txt11.ReadOnly =  false ; 
 txt12.ReadOnly =  false ; 
 txt13.ReadOnly =  false ; 
 txt14.ReadOnly =  false ; 
 txt15.ReadOnly =  false ; 
 txt16.ReadOnly =  false ; 
 txt17.ReadOnly =  false ; 
 txt18.ReadOnly =  false ; 
 txt19.ReadOnly =  false ; 
 txt20.ReadOnly =  false ; 
 txtsno.ReadOnly =  true ; 
 label13.Visible =  true ; 
 btnupdate.Visible =  true ; 
} 
 
  private   void  comboBox1_SelectedIndexChanged_1（ object  sender，EventArgs e）
 {
 btnupdate.Visible =  false ; 
 btnedit.Visible =  true ; 
 txt1.Visible =  true ; 
 txt2.Visible =  true ; 
 txtsno.Visible =  true ; 
 txt3.Visible =  true ; 
 txt4.Visible =  true ; 
 txt5.Visible =  true ; 
 txt6.Visible =  true ; 
 txt7.Visible =  true ; 
 txt8.Visible =  true ; 
 txt9.Visible =  true ; 
 txt11.Visible =  true ; 
 txt12.Visible =  true ; 
 txt13.Visible =  true ; 
 txt14.Visible =  true ; 
 txt15.Visible =  true ; 
 txt16.Visible =  true ; 
 txt17.Visible =  true ; 
 txt18.Visible =  true ; 
 txt19.Visible =  true ; 
 txt20.Visible =  true ; 
 label2.Visible =  true ; 
 label4.Visible =  true ; 
 label5.Visible =  true ; 
 label6.Visible =  true ; 
 label7.Visible =  true ; 
 label8.Visible =  true ; 
 label9.Visible =  true ; 
 label10.Visible =  true ; 
 label11.Visible =  true ; 
 label12.Visible =  true ; 
 label13.Visible =  true ; 
 label14.Visible =  true ; 
 label15.Visible =  true ; 
 label16.Visible =  true ; 
 label17.Visible =  true ; 
 label18.Visible =  true ; 
 label19.Visible =  true ; 
 label21.Visible =  true ; 
 label22.Visible =  true ; 
 label23.Visible =  true ; 
 label25.Visible =  true ; 
 label3.Visible =  true ; 
 txtsno.Visible =  true ; 
 btnexit.Visible =  true ; 
 comboBox1.Visible =  true ; 
 txt1.ReadOnly =  true ; 
 txtsno.Visible =  true ; 
 txt3.ReadOnly =  true ; 
 txt4.ReadOnly =  true ; 
 txt5.ReadOnly =  true ; 
 txt6.ReadOnly =  true ; 
 txt7.ReadOnly =  true ; 
 txt8.ReadOnly =  true ; 
 txt9.ReadOnly =  true ; 
 txt11.ReadOnly =  true ; 
 txt12.ReadOnly =  true ; 
 txt13.ReadOnly =  true ; 
 txt14.ReadOnly =  true ; 
 txt15.ReadOnly =  true ; 
 txt16.ReadOnly =  true ; 
 txt17.ReadOnly =  true ; 
 txt18.ReadOnly =  true ; 
 txt19.ReadOnly =  true ; 
 txt20.ReadOnly =  true ; 
 txtsno.ReadOnly =  true ; 
 
  string  cs =   server = 192.168.1.133; database = ComplaintReport; user id = sa; password = ssdrnd; 
 SqlConnection conn =  new  SqlConnection（cs）; 
 SqlCommand cmd =  new  SqlCommand（）; 
 尝试 
 {
 conn.Open（）; 
  int  dbsno =  int  .Parse（comboBox1.Text）; 
 
 cmd =  new  SqlCommand（ 从MRU240中选择*，其中Mno = @ dbsno，conn）; 
 cmd.Parameters.AddWithValue（  @ dbsno，dbsno）; 
 SqlDataReader dr = cmd.ExecuteReader（）; 
  if （dr.Read（））
 {
 txt1.Text = dr [  cfd]。ToString（）; 
 txt2.Text = dr [  Uno]。ToString（）; 
 txtsno.Text = dr [  Mno]。ToString（）; 
 txt3.Text = dr [  cprc]。ToString（）; 
 txt4.Text = dr [  sdc]。ToString（）; 
 txt5.Text = dr [  contact]。ToString（）; 
 txt6.Text = dr [  orderno]。ToString（）; 
 txt7.Text = dr [  ino]。ToString（）; 
 txt8.Text = dr [ 收货人]。ToString（）; 
 txt9.Text = dr [  pft]。ToString（）; 
 txt12.Text = dr [  observation]。ToString（）; 
 txt13.Text = dr [  dispatch]。ToString（）; 
 txt14.Text = dr [  repair]。ToString（）; 
 txt15.Text = dr [  cause]。ToString（）; 
 txt16.Text = dr [  userinfo]。ToString（）; 
 txt17.Text = dr [ 补救]。ToString（）; 
 txt18.Text = dr [  feedback]。ToString（）; 
 txt19.Text = dr [ 结论]。ToString（）; 
 txt20.Text = dr [  notes]。ToString（）; 
 txt11.Text = dr [ 备注]。ToString（）; 
} 
} 
  catch （例外情况）
 {
 MessageBox.Show（ex.Message） ; 
} 
 
 conn.Close（）; 
} 
 
 私有  void  btnupdate_Click_1（ object  sender，EventArgs e）
 {
  string  cs =   Data Source = 192.168.1.133; database = ComplaintReport; user id = sa; password = ssdrnd; 
 SqlConnection conn =  new  SqlConnection（cs）; 
 
  string  cfd = txt1.Text; 
  string  Uno = txt2.Text; 
  string  Mno = txtsno.Text; 
  string  cprc = txt3.Text; 
  string  sdc = txt4.Text; 
  string  contact = txt5.Text; 
  string  orderno = txt6.Text; 
  string  ino = txt7.Text; 
  string  consig = txt8.Text; 
  string  pft = txt9.Text; 
  string  remarks = txt11.Text; 
  string  obsv = txt12.Text; 
  string  disptach = txt13.Text; 
  string  repair = txt14.Text; 
  string  cause = txt15.Text; 
  string  userinfo = txt16.Text; 
  string  remedial = txt17.Text; 
  string  feedbck = txt18.Text; 
  string  conclu = txt19.Text; 
  string  notes = txt20.Text; 
  int  dbsno =  int  .Parse（comboBox1.Text）; 
 SqlCommand cmd =  new  SqlCommand（  update MRU240设置cfd = @ cfd，Uno = @ Uno，cprc = @ cprc，sdc = @ sdc，contact = @ contact，orderno = @ orderno，ino = @ ino，consignee = @ consig，pft = @ pft，remarks = @备注，观察= @ obsv，dispatch = @ dispatch，repair = @ repair，cause = @ cause，userinfo = @ userinfo，remedial = @ remedial，feedback = @ feedbck，结论= @ conclu，notes = @ notes其中Mno = @ dbsno，conn）; 
 cmd.Parameters.AddWithValue（  @ cfd，cfd）; 
 cmd.Parameters.AddWithValue（  @ Uno，Uno）; 
 cmd.Parameters.AddWithValue（  @ Mno，Mno）; 
 cmd.Parameters.AddWithValue（  @ cprc，cprc）; 
 cmd.Parameters.AddWithValue（  @ sdc，sdc）; 
 cmd.Parameters.AddWithValue（  @ contact，contact）; 
 cmd.Parameters.AddWithValue（  @ orderno，orderno）; 
 cmd.Parameters.AddWithValue（  @ ino，ino）; 
 cmd.Parameters.AddWithValue（  @ consig，consig）; 
 cmd.Parameters.AddWithValue（  @ pft，pft）; 
 cmd.Parameters.AddWithValue（  @ remarks，备注）; 
 cmd.Parameters.AddWithValue（  @ obsv，obsv）; 
 cmd.Parameters.AddWithValue（  @ dispatch，disptach）; 
 cmd.Parameters.AddWithValue（  @ repair，修复）; 
 cmd.Parameters.AddWithValue（  @ cause，cause）; 
 cmd.Parameters.AddWithValue（  @ userinfo，userinfo）; 
 cmd.Parameters.AddWithValue（  @ remedial，补救）; 
 cmd.Parameters.AddWithValue（  @ feedbck，feedbck）; 
 cmd.Parameters.AddWithValue（  @ conclu，conclu）; 
 cmd.Parameters.AddWithValue（  @ notes，notes）; 
 cmd.Parameters.AddWithValue（  @ dbsno，dbsno）; 
 
 conn.Open（）; 
  int  i =（ int ）cmd.ExecuteNonQuery（）; 
  if （i >  =  1 ）
 {
 MessageBox.Show（ 记录已更新 ）; 
 clearAll（）; 
 txt2.Text =  ; 
} 
  else  
 {
 MessageBox.Show（ 记录未更新）; 
} 
 conn.Close（）; 
} 
 
 
  private   void  txtsno_Leave（< span class =code-keyword> object  sender，EventArgs e）
 {
  if （txtsno.Text == < span class =code-string> ）
 {
 MessageBox.Show（ 请输入序列号）; 
 txtsno.Focus（）; 
} 
  if （txtsno.Text.Length >  =  7 ）
 {
 MessageBox.Show（ 输入以下7个字符）; 
 txtsno.Focus（）; 
} 
 
} 
 
 受保护 覆盖  void  OnPaint（PaintEventArgs e）
 {
 DrawIt（e.Graphics）; 
} 
 
  private   void  DrawIt（Graphics G）
 {
  //   PrintDocument document = new PrintDocument（）;  
 < span class =code-comment> //   document.PrintPage + = new PrintPageEventHandler（document_PrintPage）;  
 CaptureScreen（）; 
 
} 
  private 位图_memoryImage; 
 
 
 
  private   void  CaptureScreen（）
 {
  //  投入使用构造因为图形对象不 
  //  在离开方法范围时自动处理 
 使用（ var  myGraphics = CreateGraphics（））
 {
  var  s =大小; 
 _memoryImage =  new 位图（ 1500 ， 1000 ，myGraphics）; 
 使用（ var  memoryGraphics = Graphics.FromImage（_memoryImage））
 {
 printDocument2.DefaultPageSettings.PaperSize =  new  System.Drawing.Printing.PaperSize（  PaperA4， 826 ， 1169 ）; 
 memoryGraphics.CopyFromScreen（Location.X，Location.Y， 70 ， 30 ，s） ; 
} 
} 
} 
 私有  void  printDocument2_PrintPage （ object  sender，PrintPageEventArgs e）
 {
  //  计算考虑页边距的宽度和高度缩放 
  var  wScale = e.MarginBounds.Width /（浮）_ memoryImage.Width; 
  var  hScale = e.MarginBounds.Height /（ float ）_ memoryImage.Height; 
 
  //  选择两个比例中较小的一个 
 < span class =code-keyword> var  scale = wScale <  hScale？ wScale：hScale; 
 
  //  对图像应用缩放 
 e.Graphics .ScaleTransform（规模，比例）; 
 
  //  打印到默认打印机的页面 
 e.Graphics .DrawImage（_memoryImage， 70 ， 30 ）; 
 printDocument2.DefaultPageSettings.PaperSize =  new  System.Drawing.Printing.PaperSize（  PaperA4， 826 ， 1169 ）; 
} 
 
 
  private   void  pd_Print（< span class =code-keyword> object  sender，PrintPageEventArgs e）
 {
 DrawIt（e.Graphics）; 
} 
 
 
 私人  void  pageSetupToolStripMenuItem_Click（< span class =code-keyword> object  sender，EventArgs e）
 {
 Ps.ShowDialog（）; 
 Pd.DefaultPageSettings = Ps.PageSettings; 
 Pd.PrinterSettings = Ps.PrinterSettings; 
} 
 
  private   void  printPreviewToolStripMenuItem_Click（ object  sender，EventArgs e）
 {
 Pv.WindowState = FormWindowState.Maximized; 
 Pv.ShowDialog（）; 
} 
 
  private   void  printToolStripMenuItem_Click（ object  sender，EventArgs e）
 {
  if （Pr.ShowDialog（）== DialogResult.OK ）
 Pd.Print（）; 
} 
 
 
 
 
 
} 
}

点击页面设置我可以设置一个页面，但是它在页面中显示了一些其他代码，而点击打印预览时只显示空白页面，所以当我尝试打印时只有空白页面即将来临...所以任何人都可以帮助我，或者任何遇到此类错误的人都会帮助我。

Hi,i'm posting question for first time so if i dnt follow any threads or any mistake please excuse me...

Im getting this error in my code:
"Object reference not set to an instance of an object."

Here is my code:

 void document_PrintPage(object sender, PrintPageEventArgs e)
        {
            
            e.Graphics.DrawImage(_memoryImage, 0, 0);

        }
        private Bitmap _memoryImage;

        private void CaptureScreen()
        {
            // put into using construct because Graphics objects do not 
            //  get automatically disposed when leaving method scope
            using (var myGraphics = CreateGraphics())
            {
                var s = Size;
                _memoryImage = new Bitmap(1500, 1000, myGraphics);
                using (var memoryGraphics = Graphics.FromImage(_memoryImage))
                {
                    printDocument2.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("PaperA4", 826, 1169);
                    memoryGraphics.CopyFromScreen(Location.X, Location.Y, 70, 30, s);
                }
            }
        }

        private void printDocument2_PrintPage(object sender, PrintPageEventArgs e)
        {
             //calculate width and height scalings taking page margins into account
            var wScale = e.MarginBounds.Width / (float)_memoryImage.Width;
            var hScale = e.MarginBounds.Height / (float)_memoryImage.Height;

            // choose the smaller of the two scales
            var scale = wScale < hScale ? wScale : hScale;

            // apply scaling to the image
            e.Graphics.ScaleTransform(scale, scale);

            // print to default printer's page
            e.Graphics.DrawImage(_memoryImage, 70, 30);
            printDocument2.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("PaperA4", 826, 1169);
        }
private void btnprintpre_Click(object sender, EventArgs e)
        {
            //Associate PrintPreviewDialog with PrintDocument.
            printPreviewDialog1.Document = printDocument2;

            // Show PrintPreview Dialog
            //printPreviewDialog1.ShowDialog();

            printPreviewDialog1.WindowState = FormWindowState.Maximized;
            printPreviewDialog1.ShowDialog();
        }

And i'm getting near "var wScale = e.MarginBounds.Width / (float)_memoryImage.Width;"

So if anyone has come across this error or can solve my problem please help me.

解决方案

e.MarginBounds.Width or (float)_memoryImage.Width is returning null to the statement thats why you have error

debug your code and check whether _memoryImage variable is assigned some value or not.

Its a good practice to check for object value before using its properties.

like

if(_memoryImage != null)
{
//write your whole code here
}

<solved>
My problem got solved by changing the normal buttons to menu buttons and putting the code in it but i'm facing another error now,

Here is my complete code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Drawing.Printing;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Timers;

namespace ComplaintReport
{
    public partial class MRU240 : Form
    {

        private PrintPreviewDialog Pv;
        private PageSetupDialog Ps;
        private PrintDocument Pd;
        private PrintDialog Pr;

        private System.Windows.Forms.MainMenu mainMenu1;
        private System.Windows.Forms.MenuItem mnuFile;
        private System.Windows.Forms.MenuItem mnuSetup;
        private System.Windows.Forms.MenuItem mnuPreview;
        private System.Windows.Forms.MenuItem mnuPrint;
        private System.Windows.Forms.Button cmdQuit;

         public MRU240()
        {
            InitializeComponent();

            Pv = new PrintPreviewDialog();
            Ps = new PageSetupDialog();
            Pr = new PrintDialog();
            Pd = new PrintDocument();

            Pd.DocumentName = "My New Document";
            Pv.Document = Pd;
            Ps.Document = Pd;
            Pr.Document = Pd;
        }


       
        private void clearAll()
        {
            txt1.Text = "";
            txtsno.Text = "";
            txt3.Text = "";
            txt4.Text = "";
            txt5.Text = "";
            txt6.Text = "";
            txt7.Text = "";
            txt8.Text = "";
            txt9.Text = "";
            txt11.Text = "";
            txt12.Text = "";
            txt13.Text = "";
            txt14.Text = "";
            txt15.Text = "";
            txt16.Text = "";
            txt17.Text = "";
            txt18.Text = "";
            txt19.Text = "";
            txt20.Text = "";
       
        }
        private void newToolStripMenuItem_Click(object sender, EventArgs e)
        {
            clearAll();
        
            btnedit.Visible = false;
            btnupdate.Visible = false;
            txt1.Visible = true;
            txt2.Visible = true;
            txtsno.Visible = true;
            txt3.Visible = true;
            txt4.Visible = true;
            txt5.Visible = true;
            txt6.Visible = true;
            txt7.Visible = true;
            txt8.Visible = true;
            txt9.Visible = true;
            txt11.Visible = true;
            txt12.Visible = true;
            txt13.Visible = true;
            txt14.Visible = true;
            txt15.Visible = true;
            txt16.Visible = true;
            txt17.Visible = true;
            txt18.Visible = true;
            txt19.Visible = true;
            txt20.Visible = true;
            lbluno.Visible = false;
            label1.Visible = true;
            label2.Visible = true;
            label3.Visible = true;
            label4.Visible = true;
            label5.Visible = true;
            label6.Visible = true;
            label7.Visible = true;
            label8.Visible = true;
            label9.Visible = true;
            label10.Visible = true;
            label11.Visible = true;
            label12.Visible = true;
            label13.Visible = true;
            label14.Visible = true;
            label15.Visible = true;
            label16.Visible = true;
            label17.Visible = true;
            label18.Visible = true;
            label19.Visible = true;
            label21.Visible = true;
            label22.Visible = true;
            label23.Visible = true;
            label25.Visible = true;
            btnexit.Visible = true;
            comboBox1.Visible = false;

            txt1.ReadOnly = false;
            txt3.ReadOnly = false;
            txt4.ReadOnly = false;
            txt5.ReadOnly = false;
            txt6.ReadOnly = false;
            txt7.ReadOnly = false;
            txt8.ReadOnly = false;
            txt9.ReadOnly = false;
            txt11.ReadOnly = false;
            txt12.ReadOnly = false;
            txt13.ReadOnly = false;
            txt14.ReadOnly = false;
            txt15.ReadOnly = false;
            txt16.ReadOnly = false;
            txt17.ReadOnly = false;
            txt18.ReadOnly = false;
            txt19.ReadOnly = false;
            txt20.ReadOnly = false;
            txtsno.ReadOnly = false;
            txt2.ReadOnly = true;
        }

        private void openToolStripMenuItem_Click(object sender, EventArgs e)
        {
            string cs = "Data Source=192.168.1.133;database=ComplaintReport;user id=sa;password=ssdrnd";
            SqlConnection conn = new SqlConnection(cs);
            SqlCommand cmd = new SqlCommand();
            conn.Open();
           
            SqlDataAdapter da = new SqlDataAdapter("select Mno from MRU240", conn);
            DataSet ds = new DataSet();
            cmd = new SqlCommand("select Mno from MRU240", conn);
            da.Fill(ds, "mru240");

            comboBox1.DataSource = ds.Tables["mru240"];
            comboBox1.DisplayMember = "Mno";
            conn.Close();
           
            //btnprint.Visible = true;
            
            comboBox1.Visible = true;
            lbluno.Visible = true;
            btnupdate.Visible = false;
            txt1.Visible = false;
            txt2.Visible = false;
            txtsno.Visible = false;
            txt3.Visible = false;
            txt4.Visible = false;
            txt5.Visible = false;
            txt6.Visible = false;
            txt7.Visible = false;
            txt8.Visible = false;
            txt9.Visible = false;
            txt11.Visible = false;
            txt12.Visible = false;
            txt13.Visible = false;
            txt14.Visible = false;
            txt15.Visible = false;
            txt16.Visible = false;
            txt17.Visible = false;
            txt18.Visible = false;
            txt19.Visible = false;
            txt20.Visible = false;
            label3.Visible = false;
            label2.Visible = false;
            label4.Visible = false;
            label5.Visible = false;
            label6.Visible = false;
            label7.Visible = false;
            label8.Visible = false;
            label9.Visible = false;
            label10.Visible = false;
            label11.Visible = false;
            label12.Visible = false;
            label13.Visible = false;
            label14.Visible = false;
            label15.Visible = false;
            label16.Visible = false;
            label17.Visible = false;
            label18.Visible = false;
            label19.Visible = false;
            label21.Visible = false;
            label22.Visible = false;
            label23.Visible = false;
            label25.Visible = false;
            btnedit.Visible = false;
            
            btnexit.Visible = false;

        }

      
        private void toolStripMenuback_Click(object sender, EventArgs e)
        {
            SSCVR obj6 = new SSCVR();
            obj6.Show();
            this.Hide();
        }
       

        private void MRU240_Load(object sender, EventArgs e)
        {
            comboBox1.DropDownHeight = comboBox1.ItemHeight * 10;
            comboBox1.MouseWheel += new MouseEventHandler(comboBox1_MouseWheel);
   
            txt1.Visible = false;
            txt2.Visible = false;
            txtsno.Visible = false;
            txt3.Visible = false;
            txt4.Visible = false;
            txt5.Visible = false;
            txt6.Visible = false;
            txt7.Visible = false;
            txt8.Visible = false;
            txt9.Visible = false;
            txt11.Visible = false;
            txt12.Visible = false;
            txt13.Visible = false;
            txt14.Visible = false;
            txt15.Visible = false;
            txt16.Visible = false;
            txt17.Visible = false;
            txt18.Visible = false;
            txt19.Visible = false;
            txt20.Visible = false;
            txtsno.Visible = false;
            comboBox1.Visible = false;
            label2.Visible = false;
            label4.Visible = false;
            label5.Visible = false;
            label6.Visible = false;
            label7.Visible = false;
            label8.Visible = false;
            label9.Visible = false;
            label10.Visible = false;
            label11.Visible = false;
            label12.Visible = false;
            label13.Visible = false;
            label14.Visible = false;
            label15.Visible = false;
            label16.Visible = false;
            label17.Visible = false;
            label18.Visible = false;
            label19.Visible = false;
            label21.Visible = false;
            label22.Visible = false;
            label23.Visible = false;
            label25.Visible = false;
            label13.Visible = false;
            label3.Visible = false;
            btnupdate.Visible = false;
            btnexit.Visible = false;

        }
        void comboBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            ((HandledMouseEventArgs)e).Handled = true;
        }
        


        private void btnexit_Click(object sender, EventArgs e)
        {
            SSCVRGSE obj4 = new SSCVRGSE();
            obj4.Show();
            this.Hide();
        }



        private void saveToolStripMenuItem_Click(object sender, EventArgs e)
        {
            string cs = "Data Source=192.168.1.133;database=ComplaintReport;user id=sa;password=ssdrnd";
            SqlConnection conn = new SqlConnection(cs);
            if (txtsno.Text == "")
            {
                MessageBox.Show("Please enter serial number");
                txtsno.Focus();
            }
            if (txtsno.Text.Length >= 7)
            {
                MessageBox.Show("Serial number below 7 charachters ");
                txtsno.Focus();
            }


            try
            {
                string cfd = txt1.Text;
                string Uno = txt2.Text;
                string Mno = txtsno.Text;
                string cprc = txt3.Text;
                string sdc = txt4.Text;
                string contact = txt5.Text;
                string orderno = txt6.Text;
                string ino = txt7.Text;
                string consig = txt8.Text;
                string pft = txt9.Text;
                string remarks = txt11.Text;
                string obsv = txt12.Text;
                string disptach = txt13.Text;
                string repair = txt14.Text;
                string cause = txt15.Text;
                string userinfo = txt16.Text;
                string remedial = txt17.Text;
                string feedbck = txt18.Text;
                string conclu = txt19.Text;
                string notes = txt20.Text;
           
                SqlCommand cmd = new SqlCommand("insert into MRU240 values(@cfd,@Uno,@Mno,@cprc,@sdc,@contact,@orderno,@ino,@consig,@pft,@remarks,@obsv,@dispatch,@repair,@cause,@userinfo,@remedial,@feedbck,@conclu,@notes)", conn);
                cmd.Parameters.AddWithValue("@cfd", cfd);
                cmd.Parameters.AddWithValue("@Uno", Uno);
                cmd.Parameters.AddWithValue("@Mno", Mno);
                cmd.Parameters.AddWithValue("@cprc", cprc);
                cmd.Parameters.AddWithValue("@sdc", sdc);
                cmd.Parameters.AddWithValue("@contact", contact);
                cmd.Parameters.AddWithValue("@orderno", orderno);
                cmd.Parameters.AddWithValue("@ino", ino);
                cmd.Parameters.AddWithValue("@consig", consig);
                cmd.Parameters.AddWithValue("@pft", pft);
                cmd.Parameters.AddWithValue("@remarks", remarks);
                cmd.Parameters.AddWithValue("@obsv", obsv);
                cmd.Parameters.AddWithValue("@dispatch", disptach);
                cmd.Parameters.AddWithValue("@repair", repair);
                cmd.Parameters.AddWithValue("@cause", cause);
                cmd.Parameters.AddWithValue("@userinfo", userinfo);
                cmd.Parameters.AddWithValue("@remedial", remedial);
                cmd.Parameters.AddWithValue("@feedbck", feedbck);
                cmd.Parameters.AddWithValue("@conclu", conclu);
                cmd.Parameters.AddWithValue("@notes", notes);

                conn.Open();
                int i = cmd.ExecuteNonQuery();
                if (i == 1)
                {
                    MessageBox.Show("Record is saved ");
                    clearAll();
                }

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            conn.Close();

        }

        private void btnedit_Click_1(object sender, EventArgs e)
        {
            txt1.ReadOnly = false;
            lbluno.Visible = true;
            txt3.ReadOnly = false;
            txt4.ReadOnly = false;
            txt5.ReadOnly = false;
            txt6.ReadOnly = false;
            txt7.ReadOnly = false;
            txt8.ReadOnly = false;
            txt9.ReadOnly = false;
            txt11.ReadOnly = false;
            txt12.ReadOnly = false;
            txt13.ReadOnly = false;
            txt14.ReadOnly = false;
            txt15.ReadOnly = false;
            txt16.ReadOnly = false;
            txt17.ReadOnly = false;
            txt18.ReadOnly = false;
            txt19.ReadOnly = false;
            txt20.ReadOnly = false;
            txtsno.ReadOnly = true;
            label13.Visible = true;
            btnupdate.Visible = true;
        }

        private void comboBox1_SelectedIndexChanged_1(object sender, EventArgs e)
        {
            btnupdate.Visible = false;
            btnedit.Visible = true;
            txt1.Visible = true;
            txt2.Visible = true;
            txtsno.Visible = true;
            txt3.Visible = true;
            txt4.Visible = true;
            txt5.Visible = true;
            txt6.Visible = true;
            txt7.Visible = true;
            txt8.Visible = true;
            txt9.Visible = true;
            txt11.Visible = true;
            txt12.Visible = true;
            txt13.Visible = true;
            txt14.Visible = true;
            txt15.Visible = true;
            txt16.Visible = true;
            txt17.Visible = true;
            txt18.Visible = true;
            txt19.Visible = true;
            txt20.Visible = true;
            label2.Visible = true;
            label4.Visible = true;
            label5.Visible = true;
            label6.Visible = true;
            label7.Visible = true;
            label8.Visible = true;
            label9.Visible = true;
            label10.Visible = true;
            label11.Visible = true;
            label12.Visible = true;
            label13.Visible = true;
            label14.Visible = true;
            label15.Visible = true;
            label16.Visible = true;
            label17.Visible = true;
            label18.Visible = true;
            label19.Visible = true;
            label21.Visible = true;
            label22.Visible = true;
            label23.Visible = true;
            label25.Visible = true;
            label3.Visible = true;
            txtsno.Visible = true;
            btnexit.Visible = true;
            comboBox1.Visible = true;
            txt1.ReadOnly = true;
            txtsno.Visible = true;
            txt3.ReadOnly = true;
            txt4.ReadOnly = true;
            txt5.ReadOnly = true;
            txt6.ReadOnly = true;
            txt7.ReadOnly = true;
            txt8.ReadOnly = true;
            txt9.ReadOnly = true;
            txt11.ReadOnly = true;
            txt12.ReadOnly = true;
            txt13.ReadOnly = true;
            txt14.ReadOnly = true;
            txt15.ReadOnly = true;
            txt16.ReadOnly = true;
            txt17.ReadOnly = true;
            txt18.ReadOnly = true;
            txt19.ReadOnly = true;
            txt20.ReadOnly = true;
            txtsno.ReadOnly = true;

            string cs = "server=192.168.1.133;database=ComplaintReport;user id=sa;password=ssdrnd";
            SqlConnection conn = new SqlConnection(cs);
            SqlCommand cmd = new SqlCommand();
            try
            {
                conn.Open();
                int dbsno = int.Parse(comboBox1.Text);

                cmd = new SqlCommand("select * from MRU240 where Mno=@dbsno", conn);
                cmd.Parameters.AddWithValue("@dbsno", dbsno);
                SqlDataReader dr = cmd.ExecuteReader();
                if (dr.Read())
                {
                    txt1.Text = dr["cfd"].ToString();
                    txt2.Text = dr["Uno"].ToString();
                    txtsno.Text = dr["Mno"].ToString();
                    txt3.Text = dr["cprc"].ToString();
                    txt4.Text = dr["sdc"].ToString();
                    txt5.Text = dr["contact"].ToString();
                    txt6.Text = dr["orderno"].ToString();
                    txt7.Text = dr["ino"].ToString();
                    txt8.Text = dr["consignee"].ToString();
                    txt9.Text = dr["pft"].ToString();
                    txt12.Text = dr["observation"].ToString();
                    txt13.Text = dr["dispatch"].ToString();
                    txt14.Text = dr["repair"].ToString();
                    txt15.Text = dr["cause"].ToString();
                    txt16.Text = dr["userinfo"].ToString();
                    txt17.Text = dr["remedial"].ToString();
                    txt18.Text = dr["feedback"].ToString();
                    txt19.Text = dr["conclusion"].ToString();
                    txt20.Text = dr["notes"].ToString();
                    txt11.Text = dr["remarks"].ToString();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            conn.Close();
        }

        private void btnupdate_Click_1(object sender, EventArgs e)
        {
            string cs = "Data Source=192.168.1.133;database=ComplaintReport;user id=sa;password=ssdrnd";
            SqlConnection conn = new SqlConnection(cs);

            string cfd = txt1.Text;
            string Uno = txt2.Text;
            string Mno = txtsno.Text;
            string cprc = txt3.Text;
            string sdc = txt4.Text;
            string contact = txt5.Text;
            string orderno = txt6.Text;
            string ino = txt7.Text;
            string consig = txt8.Text;
            string pft = txt9.Text;
            string remarks = txt11.Text;
            string obsv = txt12.Text;
            string disptach = txt13.Text;
            string repair = txt14.Text;
            string cause = txt15.Text;
            string userinfo = txt16.Text;
            string remedial = txt17.Text;
            string feedbck = txt18.Text;
            string conclu = txt19.Text;
            string notes = txt20.Text;
            int dbsno = int.Parse(comboBox1.Text);
            SqlCommand cmd = new SqlCommand("update MRU240 set cfd=@cfd,Uno=@Uno,cprc=@cprc,sdc=@sdc,contact=@contact,orderno=@orderno,ino=@ino,consignee=@consig,pft=@pft,remarks=@remarks,observation=@obsv,dispatch=@dispatch,repair=@repair,cause=@cause,userinfo=@userinfo,remedial=@remedial,feedback=@feedbck,conclusion=@conclu,notes=@notes where Mno=@dbsno", conn);
            cmd.Parameters.AddWithValue("@cfd", cfd);
            cmd.Parameters.AddWithValue("@Uno", Uno);
            cmd.Parameters.AddWithValue("@Mno", Mno);
            cmd.Parameters.AddWithValue("@cprc", cprc);
            cmd.Parameters.AddWithValue("@sdc", sdc);
            cmd.Parameters.AddWithValue("@contact", contact);
            cmd.Parameters.AddWithValue("@orderno", orderno);
            cmd.Parameters.AddWithValue("@ino", ino);
            cmd.Parameters.AddWithValue("@consig", consig);
            cmd.Parameters.AddWithValue("@pft", pft);
            cmd.Parameters.AddWithValue("@remarks", remarks);
            cmd.Parameters.AddWithValue("@obsv", obsv);
            cmd.Parameters.AddWithValue("@dispatch", disptach);
            cmd.Parameters.AddWithValue("@repair", repair);
            cmd.Parameters.AddWithValue("@cause", cause);
            cmd.Parameters.AddWithValue("@userinfo", userinfo);
            cmd.Parameters.AddWithValue("@remedial", remedial);
            cmd.Parameters.AddWithValue("@feedbck", feedbck);
            cmd.Parameters.AddWithValue("@conclu", conclu);
            cmd.Parameters.AddWithValue("@notes", notes);
            cmd.Parameters.AddWithValue("@dbsno", dbsno);
          
            conn.Open();
            int i = (int)cmd.ExecuteNonQuery();
            if (i >= 1)
            {
                MessageBox.Show("Record is updated ");
                clearAll();
                txt2.Text = "";
            }
            else
            {
                MessageBox.Show("Record is not updated");
            }
            conn.Close();
        }
       

        private void txtsno_Leave(object sender, EventArgs e)
        {
            if (txtsno.Text == "")
            {
                MessageBox.Show("Please enter serial number");
                txtsno.Focus();
            }
            if (txtsno.Text.Length >= 7)
            {
                MessageBox.Show("Enter below 7 charachers ");
                txtsno.Focus();
            }

        }

        protected override void OnPaint(PaintEventArgs e)
        {
            DrawIt(e.Graphics);
        }

        private void DrawIt(Graphics G)
        {
            //PrintDocument document = new PrintDocument();
            //document.PrintPage += new PrintPageEventHandler(document_PrintPage);
            CaptureScreen();

        }
        private Bitmap _memoryImage;



        private void CaptureScreen()
        {
            // put into using construct because Graphics objects do not 
            //  get automatically disposed when leaving method scope
            using (var myGraphics = CreateGraphics())
            {
                var s = Size;
                _memoryImage = new Bitmap(1500, 1000, myGraphics);
                using (var memoryGraphics = Graphics.FromImage(_memoryImage))
                {
                    printDocument2.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("PaperA4", 826, 1169);
                    memoryGraphics.CopyFromScreen(Location.X, Location.Y, 70, 30, s);
                }
            }
        }
        private void printDocument2_PrintPage(object sender, PrintPageEventArgs e)
        {
            // calculate width and height scalings taking page margins into account
            var wScale = e.MarginBounds.Width / (float)_memoryImage.Width;
            var hScale = e.MarginBounds.Height / (float)_memoryImage.Height;

            // choose the smaller of the two scales
            var scale = wScale < hScale ? wScale : hScale;

            // apply scaling to the image
            e.Graphics.ScaleTransform(scale, scale);

            // print to default printer's page
            e.Graphics.DrawImage(_memoryImage, 70, 30);
            printDocument2.DefaultPageSettings.PaperSize = new System.Drawing.Printing.PaperSize("PaperA4", 826, 1169);
        }


        private void pd_Print(object sender, PrintPageEventArgs e)
        {
            DrawIt(e.Graphics);
        }


        private void pageSetupToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Ps.ShowDialog();
            Pd.DefaultPageSettings = Ps.PageSettings;
            Pd.PrinterSettings = Ps.PrinterSettings;
        }

        private void printPreviewToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Pv.WindowState = FormWindowState.Maximized;
            Pv.ShowDialog();
        }

        private void printToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (Pr.ShowDialog() == DialogResult.OK)
                Pd.Print();
        }

      
       

       
    }
}

While clicking on page setup i'm able to setup a page but it is showing me some other code in the page and while clicking on print preview is displaying only blank page so when i try to take print only blank page is coming...So can anyone help me from this or anyone who came across this type of error help me out.

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错误：对象引用未设置为对象的实例。 [英] Error: Object reference not set to an instance of an object.

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错误：对象引用未设置为对象的实例。 [英] Error: Object reference not set to an instance of an object.

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