ASP.NET 切换控制隐藏代码的可见性

发布于 2024-12-12 09:58:19 字数 1082 浏览 0 评论 0原文

我有两个问题，我不确定是否相关：

我有两个 DropDownList 控件（最初设置为不可见）和一个 RadioButtonList 控件，其自动回发行为设置为 true。

每当回发发生时，我想从 RadioButtonList 控件中读取 SelectedValue 属性 - 并根据该属性，使 DropDownList 之一可见。

这是我的问题：

1）我无法通过 ID 直接引用 RadioButtonList 控件。 Designer.cs 文件似乎没有生成 RadioButtonList 或 DropDownList 控件。即使我手动将控件添加到 Designer.cs 文件中，它们也会在重新生成时丢失。这是预期的行为吗？

2）我尝试在 Page_Load() 方法中使用 Page.FindControl 属性。

if(Page.PostBack==true)
{
    RadioButtonList rbl = (RadioButtonList)Page.FindControl("RadioButtonList1");
    if(rbl.SelectedValue=="optionA")
    {
         DropDownList ddA = (DropDownList)Page.FindControl("DropDownListA");
         ddA.Visible = true;   
    }
    else
    {
         DropDownList ddB = (DropDownList)Page.FindControl("DropDownListB");
         ddB.Visible=true;
    }
}

但我在 if 条件下收到 NullReferenceException 。

我完全走错路了吗？有人会指导我实现我想做的事情的最佳方法吗？

另外，我该怎么做才能使 Designer.cs 文件加载控件？

编辑：/facepalm

我自己想出来了。我忘记了我正在使用表格内的控件。

一旦我将控件移到表之外，我就可以直接引用 ID。

睡眠不足和咖啡是罪魁祸首。我很抱歉。谢谢您的帮助！

原文

I have two problems that I'm not sure are related:

I have two DropDownList controls (initially set to not visible) and a RadioButtonList control with autopostback behaviour set to true.

Whenever Postback occurs, I want to read the SelectedValue property from the RadioButtonList control - and depending on that, make one of the DropDownLists visible.

Here's my problem:

1) I can't directly refer to the RadioButtonList control by its ID. The designer.cs file doesn't seem to generate either the RadioButtonList or DropDownList controls. Even if I manually add the controls to the designer.cs file, they are lost upon regenerating. Is this expected behaviour?

2) I tried using the Page.FindControl property in the Page_Load() method.

if(Page.PostBack==true)
{
    RadioButtonList rbl = (RadioButtonList)Page.FindControl("RadioButtonList1");
    if(rbl.SelectedValue=="optionA")
    {
         DropDownList ddA = (DropDownList)Page.FindControl("DropDownListA");
         ddA.Visible = true;   
    }
    else
    {
         DropDownList ddB = (DropDownList)Page.FindControl("DropDownListB");
         ddB.Visible=true;
    }
}

But I'm getting a NullReferenceException at the if condition.

Am I completely on the wrong track? Will someone guide me about the best way to achieve what I want to do?

Also, what can I do to make designer.cs file load the Controls?

EDIT: /facepalm

I figured it out myself. I'd forgotten than I'm using the control inside a table.

Once I moved the Control outside the Table, I could refer to the ID directly.

A lack of sleep and coffee to blame. My apologies. Thank you for the help!

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好菇凉咱不稀罕他 2024-12-19 09:58:19

Page.FindControl 不是递归的，即如果 dropdownlist1 控件位于其他控件中，它将返回 null。
检查此链接了解详细信息，看看您是否能够正确找到下拉列表。

http://www.mha.dk/post/Recursive-PageFindControl.aspx< /a>

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恏ㄋ傷疤忘ㄋ疼 2024-12-19 09:58:19

您正在为 rb1.SelectedValue 分配一个值，并且应该检查是否找到该控件。

if(rb1.SelectedValue="optionA")

应该是

if(rb1.SelectedValue != null)
{ 
   if(rb1.SelectedValue == "optionA")
   {
       DropDownList ddA = (DropDownList)Page.FindControl("DropDownListA"); 

       if (ddA != null)
                 ddA.Visible = true;  
   }
}

You are assigning a value to rb1.SelectedValue and you should check if the control was found.

if(rb1.SelectedValue="optionA")

should be

if(rb1.SelectedValue != null)
{ 
   if(rb1.SelectedValue == "optionA")
   {
       DropDownList ddA = (DropDownList)Page.FindControl("DropDownListA"); 

       if (ddA != null)
                 ddA.Visible = true;  
   }
}

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