UserControl上的自定义事件 [英] Custom event on UserControl

问题描述

如果找到了一段代码，使您可以在用户控件上创建自己的事件.伟大的！但这对我不起作用.这是(已更改为我的情况)代码:

用户控件:

Hi,

If have found a piece of code that allows you to create own events on a usercontrol. Great! But it doesn''t work with me. This is the (changed to my situation) code:

Usercontrol:

public partial class Usercontrols_Modal : System.Web.UI.UserControl
{
    public delegate void ResultCompletedEventHandler(object sender, ReturnResultArgs e);
    public event ResultCompletedEventHandler ReturnResult;

    protected void btnYes_Click(object sender, EventArgs e)
    {
        ReturnResultArgs args = new ReturnResultArgs();
        args.Result = true;
        this.ReturnResult(this, args);
    }
}

public class ReturnResultArgs : EventArgs
{
    // this is a string value I will set using a dropdownlist
    public Boolean Result { get; set; }
}

在网络表单上(后面的代码):

On the webform (code behind):

public void AskQuestion(object sender, EventArgs e)
{
    modaldelete.ReturnResult +=new Usercontrols_Modal.ResultCompletedEventHandler(modaldelete_ReturnResult);
    //modaldelete.SearchCompleted +=new Usercontrols_Modal.SearchCompletedEventHandler(modaldelete_SearchCompleted);
    modaldelete.Visible = true;
}

protected void modaldelete_ReturnResult(object sender, ReturnResultArgs e)
{
    Response.Redirect("/default.aspx");
}

我的代码在this.ReturnResult(this，args);上中断.看来ReturnResult为null，无法继续.

我做错了什么?

在此先感谢

My code breaks on this.ReturnResult(this, args);. It seems ReturnResult is null and cannot continue.

What am I doing wrong??

Thanks in advance

推荐答案

在触发该事件之前始终检查该事件是否具有订阅者:

Always check that the event has subscribers before firing it:

if (this.ReturnResult != null) {
        ReturnResultArgs args = new ReturnResultArgs();
        args.Result = true;
        this.ReturnResult(this, args);
}

如果在AskQuestion中订阅事件之前执行了btnYes_Click，那么您将得到所提到的错误.

If btnYes_Click is executed before the event is subscribed in AskQuestion, then you would get the error mentioned.

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