由于contentPage，对象引用未设置为对象的实例 [英] Object reference not set to an instance of an object due to the contentPage

问题描述

我有一个继承的主页和内容页面，因此在我的一个内容页面中，我正在使用此代码：

 <   asp：内容    ID   =  Content2    ContentPlaceHolderID   =  ContentPlaceHolder1    Runat   = 服务器 >  
 <   div  >  
 <   asp：TextBo x     ID   =  txtNumber    runat   =  server >  
 <   / asp：TextBox  >  
 <   br     /  >  
 <   asp：按钮    ID   =  btn    runat   =  server   文字  = 生成    /  >  
 <   asp：Panel     ID   =  pnlDate < span class =code-attribute>   runat   =  server >  
 <   / asp：Panel  >  
 &l t;   / div  >  
 <   div  >  
 <   asp：按钮    ID   =  btnSave    runat   =  server   文字  = 保存    OnClick   =   btn_Click    /  >  
 <   asp：标签    ID   =  lblInsert    runat   = 服务器 >  < span class =code-keyword><   / asp：Label  >  
 <   / div  >  
 <   / asp：Content  > ;  

，背后的代码是：

 protected void Page_Load（对象发送r，EventArgs e）
 {
 GenerateTxtB（）; 
} 
 protected void GenerateTextBoxes_onClick（object sender，EventArgs e）
 {
 pnlDate.Controls.Clear（）; 
 GenerateTxtB（）; 
} 
 
 private void GenerateTxtB（）
 {
 if（txtNumber.Text！= string.Empty）
 {
 int number = Convert.ToInt32（txtNumber.Text）; 
 string top =; 
 int left = 0; 
 
 TextBox txt; 
表tb = new Table（）; 
 tb.ID =tb1; 
 TableRow tr = new TableRow（）; 
 
 for（int i = 1; i< = number; i ++）
 {
 Label lb = new Label（）; 
 lb.ID =lbFname+ i.ToString（）; 
 lb.Text =名字：; 
 
 txt = new TextBox（）; 
 txt.ID =textBox+ i.ToString（）; 
 txt.Attributes.Add（runat，server）; 
 
 txt.CssClass =myDates; 
 txt.Width = Unit.Pixel（240）; 
 txt.MaxLength = 1; 
 txt.EnableViewState = true; 
 txt.Style.Add（HtmlTextWriterStyle.Position，relative）; 
 txt.Style [HtmlTextWriterStyle.Left] = left +px; 
剩下+ = 5; 
 
 
 RequiredFieldValidator rf = new RequiredFieldValidator（）; 
 rf.ControlToValidate =textBox+ i.ToString（）; 
 rf.ID =RF+ i.ToString（）; 
 rf.Text =需要日期; 
 rf.ForeColor = System.Drawing.Color.Red; 
 rf.ErrorMessage =需要日期; 
 rf.Display = ValidatorDisplay.Dynamic; 
 rf.SetFocusOnError = true; 
 pnlDate.Controls.Add（rf）; 
 
 
 TableCell tc = new TableCell（）; 
 tc.Controls.Add（txt）; 
 tr.Controls.Add（tc）; 
 tb.Controls.Add（tr）; 
 pnlDate.Controls.Add（tb）; 
 
} 
 
} 
 
} 
 public void btn_Click（object sender，EventArgs e）
 {
表t =（表）Page.FindControl（pnlDate）。FindControl（tb1）; 
 TextBox文本框; 
 
 foreach（TableRow tr in t.Rows）
 {
 foreach（TableCell tc in tr.Cells）
 {
 foreach（Control c in tc） .Controls）
 {
 if（c.GetType（）== typeof（TextBox））
 {
 textbox =（TextBox）c; 
 
 
 
 Response.Write（TextBox Value is：+ textbox.Text +< br />）; 
 
 
} 
} 
} 
} 
} 

这个代码wotk在页面中没有继承主页而不是在contentPage中，我收到此错误：

Quote：

对象引用未设置为对象的实例。

...

它指向这行代码：

Quote：

表t =（表）Page.FindControl（pnlDate）。FindControl（tb1）;

请一些人告诉我为什么和如何解决这个问题。

解决方案

您是否在 tb1 的定义> pnlDate 元素？我不能，所以我会得出与错误完全相同的结论。



祝你好运！

把这一行排除在外for for循环：

 pnlDate.Controls.Add（tb）; 

参考此主题

http://forums.asp.net/t/ 1807044.aspx [ ^ ]

和本文

http://www.dotnetcurry.com/ ShowArticle.aspx？ID = 135 [ ^

Hi, I have a masterpage and contentpages that inherit from it so in one of my contentPage I am putting this code:

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <div>
        <asp:TextBox ID="txtNumber" runat="server">
        </asp:TextBox>
        <br />
        <asp:Button ID="btn" runat="server" Text="Generate" />
        <asp:Panel ID="pnlDate" runat="server">
        </asp:Panel>
    </div>
    <div>
        <asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btn_Click" />
        <asp:Label ID="lblInsert" runat="server"></asp:Label>
    </div>
</asp:Content>

and the code behind is:

protected void Page_Load(object sender, EventArgs e)
    {
        GenerateTxtB();
    }
    protected void GenerateTextBoxes_onClick(object sender, EventArgs e)
    {
        pnlDate.Controls.Clear();
        GenerateTxtB();
    }
 
    private void GenerateTxtB()
    {
        if (txtNumber.Text != string.Empty)
        {
             int number = Convert.ToInt32(txtNumber.Text);
            string top = "";
            int left = 0;

            TextBox txt;
            Table tb = new Table();
            tb.ID = "tb1";
            TableRow tr = new TableRow();

            for (int i = 1; i <= number; i++)
            {
                Label lb = new Label();
                lb.ID = "lbFname" + i.ToString();
                lb.Text = "First Name :";

                txt = new TextBox();
                txt.ID = "textBox" + i.ToString();
                txt.Attributes.Add("runat", "server");

                txt.CssClass = "myDates";
                txt.Width = Unit.Pixel(240);
                txt.MaxLength = 1;
                txt.EnableViewState = true;
                txt.Style.Add(HtmlTextWriterStyle.Position, "relative");
                txt.Style[HtmlTextWriterStyle.Left] = left + "px";
                left += 5;


                RequiredFieldValidator rf = new RequiredFieldValidator();
                rf.ControlToValidate = "textBox" + i.ToString();
                rf.ID = "RF" + i.ToString();
                rf.Text = "Date are required";
                rf.ForeColor = System.Drawing.Color.Red;
                rf.ErrorMessage = "Date is required";
                rf.Display = ValidatorDisplay.Dynamic;
                rf.SetFocusOnError = true;
                pnlDate.Controls.Add(rf);


                TableCell tc = new TableCell();
                tc.Controls.Add(txt);
                tr.Controls.Add(tc);
                tb.Controls.Add(tr);
                pnlDate.Controls.Add(tb);

            }

        }

    }
    public void btn_Click(object sender, EventArgs e)
    {
        Table t = (Table)Page.FindControl("pnlDate").FindControl("tb1");
        TextBox textbox;

        foreach (TableRow tr in t.Rows)
        {
            foreach (TableCell tc in tr.Cells)
            {
                foreach (Control c in tc.Controls)
                {
                    if (c.GetType() == typeof(TextBox))
                    {
                        textbox = (TextBox)c;



                        Response.Write("TextBox Value is:" + textbox.Text + "<br/>");
                       
        
                    }
                }
            }
        }
    }

This code wotk in page that doest not inherit the master page but not in a contentPage, I am getting this error:

Quote:

Object reference not set to an instance of an object.

...
It is pointing to this line of code :

Quote:

Table t = (Table)Page.FindControl("pnlDate").FindControl("tb1");

Please can some tell me why and how to resolve this issue.

解决方案

Do you see a definition of tb1 within the pnlDate element? I cannot, so I would come to the exact same conclusion as the error.

Good luck!

put this line out of for loop :

pnlDate.Controls.Add(tb);

Refer this thread
http://forums.asp.net/t/1807044.aspx[^]
and this article
http://www.dotnetcurry.com/ShowArticle.aspx?ID=135[^]

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