Combobox与表列值 [英] Combobox with a Table Column Values

问题描述

  public   partial   class  New_Quote：表格
 {
  public   string  busnamevar =  ; 
  public  New_Quote（）
 {
 InitializeComponent（）; 
 st =   value; 
 FillCombo（）; 
} 
  void  FillCombo（）
 {
 
  string  sql =  从new_customer中选择cusname，其中busname =' + st +  '; 
  //   **** string sql =从new_customer中选择cusname，其中busname ='+ busnamevar + ;  
 
 MySqlDataReader阅读器; 
 尝试 
 {
 con =  new  MySqlConnection（str）; 
 con.Open（）; 
 MySqlCommand cmd =  new  MySqlCommand（sql，con）; 
 
 reader = cmd.ExecuteReader（）; 
  while （reader.Read（））
 {
  string  scname = reader.GetString（  cusname）; 
 comboBox1.Items.Add（scname）; 
} 
} 
  catch （MySqlException ex）
 {
 MessageBox.Show（ex.ToString（ ））; 
} 
} 

如果我在where子句中使用busnamest中指定的值那么它工作正常，但如果我使用公共字符串变量busnamevar，则comobobox不包含表列中的值。



我试图将公共字符串复制到本地变量但是它不起作用

解决方案

你的吗？如果总线名称为空，则select语句返回值???

您设置

 busnamevar =  ; 

并且您没有为变量指定任何名称。请指定一些名称并查看其是否有效



已编辑：由于OP提到他正在传递另一种形式的价值



选中此项以了解如何在表格之间传递值



[ ^ ]



希望它有所帮助



更新：



而不是将变量busnamevar声明为字符串varibale，将其声明为属性

并在设置值后调用方法Fillcombo < br $> b $ b

  private   string  _busnamevar =  string  .Empty; 
  public   string  Busnamevar 
 {
  get  
 {
  return  _busnamevar; 
} 
  set  
 {
 _busnamevar =  value  ; 
 FillCombo（）; 
} 
} 
 

查询应为

< pre lang =c＃> string sql = 选择来自new_customer的cusname，其中busname =' + Busnamevar + ';

 public partial class New_Quote : Form
    {
        public string busnamevar = "";
public New_Quote()
        {
            InitializeComponent();
            st = "value";
            FillCombo();
        }
  void FillCombo()
        {
           
            string sql = "select cusname from new_customer where busname='"+st+"'";
     //**** string sql = "select cusname from new_customer where busname='"+busnamevar+"'";  
           
            MySqlDataReader reader; 
            try
            {
                con = new MySqlConnection(str);
                con.Open();
              MySqlCommand cmd = new MySqlCommand(sql, con);                
                   
                reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    string scname = reader.GetString("cusname");
                    comboBox1.Items.Add(scname);
                }
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

If i use busname in where clause the value specified in the "st" then it is working fine but if I use the "public string variable busnamevar" then comobobox not contains the values from the table column.

I tried to copy the public string to local variable but it is not working

解决方案

does your select statement returns values if the busname is empty???
you set

busnamevar = "";

and you are not assigning any name for the variable.Assign some name and see whether it works or not

Edited: As the OP mentioned that he is passing value from another form

Check this to know how to pass values between the forms

passing values between two windows forms[^]

Hope it helps

Update:

Instead of declaring the variable busnamevar as a string varibale,declare it as a property
and call the method Fillcombo once the value is set

private string _busnamevar = string.Empty;
       public string Busnamevar
       {
           get
           {
               return _busnamevar;
           }
           set
           {
               _busnamevar = value;
               FillCombo();
           }
       }

The query should be

string sql = "select cusname from new_customer where busname='"+Busnamevar+"'";

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