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正在使用-=-运算符注销事件

event-handling events winforms c#

Matthias Meid · 技术社区 · 17 年前

打开窗口时,我在业务对象上注册了一个“已删除”事件处理程序。它以如下方式传递给构造函数 business :

business.Deleted += new EventHandler<EventArgs>(business_Deleted);

现在,用户可以单击按钮删除它(删除记录,你知道的)。事件处理程序被注册为捕获其他编辑器窗口的删除并通知用户(“项目已在另一个编辑器窗口中删除。”)。

如果用户在当前窗口中删除它,这条消息将是愚蠢的,所以我想在之前注销该事件:

Business business = (Business)businessBindingSource.DataSource;
business.Deleted -= new EventHandler<EventArgs>(business_Deleted);

我的问题很简单:无论如何都会显示消息,因此注销不起作用。我尝试将事件处理程序存储在单独的成员中。也不起作用。

任何帮助都会很酷。

马蒂亚斯

P.S.阅读 this post ,恐怕正确注销该事件可能会使其在所有编辑器窗口中都未注册。这可能是下一个问题。 ;-)

5 回复 | 直到 9 年前

TcKs 17 年前

如果你真的想要这种行为(我不认为,这是一个好的模式,但没关系),你可以从ViewModel类派生,并为删除的作者添加属性。然后,您可以执行以下操作:

c.Delete( this ); //this = window
// ...
void business_Deleted(object sender, EventArgs e) {
    bool isDeletedFromMe = false;
    if ( e is DeletedEventArgs ) { isDeletedFromMe = object.ReferenceEquals( this, e.Author ); }
    if ( false == isDeletedFromMe ) {
        MessageBox.Show("Item has been deleted in another editor window.",
            "...", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        Close();
    }
}

或者你可以这样做:

void business_Deleted(object sender, EventArgs e)
{
    if ( false == object.ReferenceEquals( sender, this.currentlyDeletingBusiness ) ) {
        MessageBox.Show("Item has been deleted in another editor window.",
            "...", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
    }
    Close();
}

Business currentlyDeletingBusiness;
private void deleteButton_Activate(object sender, EventArgs e)
{
    Business c = (Business)businessBindingSource.DataSource;
    try {
        this.currentlyDeletingBusiness = c;
        c.Delete();
    }
    finally {
        this.currentlyDeletingBusiness = null;
    }
}

Yona 17 年前

我不知道为什么您的示例代码不能按预期工作,但您可以尝试添加一个私有成员变量,以检查此用户是删除记录还是其他用户。

private bool otherUser = true;

void business_Deleted(object sender, EventArgs e)
{
    if(otherUser) {
        /* Show message */
    }
}

void deleteButton_Activate(object sender, EventArgs e)
{
    otherUser = false;
    /* Delete record */
}

SwDevMan81 17 年前

活动可以注册多次吗?我会在后面加一个断点

business.Deleted -= new EventHandler(business_Deleted);

查看业务的_invocationCount和_invocationList。已删除(在“基础”->“非公开成员”下),以确保不再注册任何事件。

Ed Swangren 17 年前

从我看到的几行文字来看,这可能是问题所在:

Business business = (Business)businessBindingSource.DataSource;

看起来您正在将业务所持有的引用更改为另一个对象。也许你的只是一个例子,你每次都在使用同一个对象。

Tim Cooper 14 年前

当然,这是最短的完整示例:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication
{
    public partial class BusinessEditor : Form
    {
        private EventHandler<EventArgs> businessDeletedHandler;

        public BusinessEditor(Business business)
            : this()
        {
            InitializeComponent();

            businessBindingSource.DataSource = business;

            // Registering
            businessDeletedHandler = new EventHandler<EventArgs>(business_Deleted);
            business.Deleted += businessDeletedHandler;
        }

        void business_Deleted(object sender, EventArgs e)
        {
            MessageBox.Show("Item has been deleted in another editor window.",
                "...", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            Close();
        }

        private void deleteButton_Activate(object sender, EventArgs e)
        {
            Business c = (Business)businessBindingSource.DataSource;
            // Unregistering
            c.Deleted -= businessDeletedHandler;
            c.Delete();
            Close();
        }
    }
}

我想应该是同一个例子,埃德。我说得对吗?

问候,谢谢你!