这段代码给我错误(System.NullReferenceException:对象引用未设置为对象的实例.) [英] This code give me error( System.NullReferenceException: Object reference not set to an instance of an object.)

问题描述

private void ReadTextBoxes()
{
    string strValue = string.Empty;
    int n = NumberOfControls;
    Panel pnl = (Panel)Page.FindControl("Panel1");

    for (int i = 0; i <= NumberOfControls; i++)
    {
        //:confused: This line Give me error please give me solution
        string boxName = "TextBoxID" + (i + 1).ToString();


        TextBox tb = pnl.FindControl(boxName) as TextBox;
        strValue += tb.Text + "\n";

    }
    Response.Write(strValue);

}

推荐答案

您要么将Panel Object值获取为null，要么将Textbox Object值获取为null.


原因1:
错误行必须为:
strValue + = tb.Text +"\ n";

我看到的Issue1:

Either you are getting Panel Object value as null or textbox Object value as null.


REASON 1:
Error line must be:
strValue += tb.Text + "\n";

Issue1 to me looks at:

strValue += tb.Text + "\n";

看起来您在这里获取tb值的"null":

Looks like you are getting "null" for tb value here:

TextBox tb = pnl.FindControl(boxName) as TextBox;

原因:

Reason:

string boxName = "TextBoxID" + (i + 1).ToString();

原因2:
错误行必须为:
TextBox tb = pnl.FindControl(boxName)作为TextBox;

如果pnl值为null，则此行将引发错误.

我看到的Issue2:

REASON 2:
Error line must be:
TextBox tb = pnl.FindControl(boxName) as TextBox;

If pnl value is null, then this line would throw an error.

Issue2 to me looks at:

TextBox tb = pnl.FindControl(boxName) as TextBox;

看起来您在这里获取"null"的pnl值:

Looks like you are getting "null" for pnl value here:

Panel pnl = (Panel)Page.FindControl("Panel1");

检查您是否有名为"Panel1"的面板.

===========
我认为您指定的位置肯定不会出错.

Check that you have "Panel1" named Panel with you.

===========
I don''t think you must be getting error at the location specified by you.

string boxName = "TextBoxID" + (i + 1).ToString();

这句话没有错.

There is nothing wrong with this statement.

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