运行时生成控件给出错误 [英] Runtime generate control give error

问题描述

大家好，

我正在创建一个网站.
我有一个面板，按钮和组合框.
组合框用于选择否.运行时生成的文本框的数量，该按钮用于在文本框中显示所有运行时生成的文本.

我已经试过了这段代码，但它给出了一个错误:-

Hi All,

I am creating a website.
I have a Panel, button, and combo-box.
The combobox is used for selecting no. of textbox you generate at runtime and the button is used for displaying all runtime generated text in the textbox.

I have tried this code but it gives an error:-

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class NewFolder1_AutoGenerate : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        int indexcount=int.Parse(DropDownList1.SelectedValue);
        for (int i = 0; i < indexcount; i++)
        {
            TextBox t1 = new TextBox();
            t1.ID = "text" + i.ToString();
            Panel1.Controls.Add(t1);
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string s1 = null;
        foreach (Control ctrl in Panel1.Controls)
        {
            TextBox t1 = (TextBox)ctrl;
            s1 += t1.Text + "/n";
        }
        Response.Write(Panel1.Controls.Count.ToString());
 Response.Write(s1);
    }
}

上面的代码生成了运行时控件，但是当我单击按钮时，它不会显示所有文本框文本.

它给出错误:-
(InvalidCastException)无法将类型为"System.Web.UI.LiteralControl"的对象转换为类型为"System.Web.UI.WebControls.TextBox".

帮帮我.

The above code generates the runtime control but when I click the button it does not display the all textbox text.

It give error:-
(InvalidCastException) Unable to cast object of type ''System.Web.UI.LiteralControl'' to type ''System.Web.UI.WebControls.TextBox''.

Help me.

推荐答案

那是因为面板中还有其他控件，它们不是Textboxes-在使用它们之前请检查一下:

That''s because there are other controls in the panel, which are not Textboxes - check before you use them:

foreach (Control ctrl in Panel1.Controls)
   {
   TextBox t1 = ctrl as TextBox;
   if (t1 != null)
      {
      s1 += t1.Text + "/n";
      }
   }

您必须在投射之前检查控件.

You have to check the control before casting.

if (ctrl.GetType().Name.ToString()=="TextBox")
{
TextBox t1 = (TextBox)ctrl;
 s1 += t1.Text + "/n";
}

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