如何在c＃中使用带有集合的事件处理程序 [英] how to use event handlers with collections in c#

问题描述

您好，



我想检测队列中是否添加了某些项目或者列表。在添加该项目时，我必须弹出一条消息。我尝试过很多东西，但是工作很有用。



简单来说，如何使用集合处理事件处理。





谢谢和问候

解决方案

你看过 ObservableCollection [ ^ ]？它实现 INotifyPropertyChanged 和 INotifyCollectionChanged 开箱即用。看起来这正是您正在寻找的。

首先检查： List vs ObservableCollection vs Silverlight中的INotifyPropertyChanged [ ^ ]

解决此问题的最佳方法是使用.NET的'ObservableCollection及其INotify___工具。



有些人真的很难掌握这个，我建议你通过研究.NET中定义自定义事件的标准方法来做好准备：[ ^ ]。



这是一个继承自List< int>的类的示例...它是一个通用的整数集合...它实现了一个自定义事件：

 使用系统; 
 使用 System.Collections.Generic; 
 
 命名空间 Jan_1_2014_CollectionWithNotification 
 {
  public   class  CustomIntCollection：List< int> 
 {
  //  我们要公开整数的值 
  //  当前正被添加到集合中 
  //  需要自定义EventArgs类 
  //  此处此类嵌套在集合中 
  //   ......可以在集合之外定义 
  public   class  NewIntAddEventArgs：EventArgs 
 {
  public   int  intValue {获得;  set ; } 
 
  public  NewIntAddEventArgs（ int  theInt）{intValue = theInt; } 
} 
 
  //  这是可用的EventHandler方法 
  //  由此类消费者订阅 
  public   event  EventHandler< NewIntAddEventArgs> NewIntAdded; 
 
  public   void 添加（ int  newInt）
 {
  //  调用自定义事件 
 OnRaiseNewIntAdded（ new  NewIntAddEventArgs（newInt））; 
 
  //  让基本内部集合处理'添加 
  base  .Add（newInt）; 
} 
 
  //  遵循标准MS C＃的自定义事件代码 
  //  提升自定义事件的标准 
  protected   virtual   void  OnRaiseNewIntAdded（NewIntAddEventArgs e）
 { 
 EventHandler< NewIntAddEventArgs> handler = NewIntAdded; 
 
  //  仅在有订阅者的情况下触发事件！ 
  if （handler！=  null ）handler（ this ，e）; 
} 
} 
} 

您可以像这样测试此类的通知事件工具：

  //  在某个表单中 
 CustomIntCollection cIntCollection =  new  CustomIntCollection（ ）; 
 
  private   void  SomeForm_Load（对象 sender，EventArgs e）
 {
  //  将EventHandler绑定到此实例 
 cIntCollection.NewIntAdded + = cIntCollection_NewIntAdded; 
} 
 
  //  现在绑定到CustomIntCollection实例的EventHandler： 
  private   void  cIntCollection_NewIntAdded（ object  sender，CustomIntCollection.NewIntAddEventArgs e）
 {
 Console.WriteLine（  the integer added = + e.intValue.ToString（））; 
} 
 
  //  代码中方法内的某处 
  //  测试为实例添加int和int的范围： 
 cIntCollection.Add（ 100 ）; 
 cIntCollection.AddRange（ new  List< int> { ， 2 ， 3 ， 4 }）; 

创建遵循MS准则的自定义事件的代码（是的，您可以通过其他方式完成）并使用它们，对于C＃的新生来说，通常看起来很奇怪，但是你会习惯它，我相信，你会发现，似乎很多额外的工作与允许：



1.代码中的安全：防止 - 效果



2.创建在继承类中可以覆盖的结构/方法。





[edit]编辑v3 [Nelek]第一个代码块从xml更改为c＃以改善颜色格式和可读性[/ edit]

[edit]编辑v4 [Nelek]编辑v3和海报请求中此行的更改说明[/ edit]

Hello,

I want to detect if some item was added in a queue let us say or a list. On the addition of that item i must get a message pop up. I have tried many things but dint work.

In simple words how to use event handling with collections.


Thanks and regards

解决方案

Have you had a look at ObservableCollection[^] yet? It implements INotifyPropertyChanged and INotifyCollectionChanged out of the box. Looks like that's exactly what you are looking for.

Check this first: List vs ObservableCollection vs INotifyPropertyChanged in Silverlight[^]

The best way to approach this is to use .NET's 'ObservableCollection, and its INotify___ facilities.

Some people really struggle with mastering this, and I recommend you prepare yourself by studying the standard way custom events are defined in .NET: [^].

Here's an example of a Class that inherits from List<int> ... it's a generic collection of integers ... which implements a custom event:

using System;
using System.Collections.Generic;

namespace Jan_1_2014_CollectionWithNotification
{
    public class CustomIntCollection : List<int>
    {
        // we want to expose the value of the integer
        // that is currently being added to the collection
        // that requires a custom EventArgs class
        // here this class is nested within the collection
        // ... it could be defined outside the collection
        public class NewIntAddEventArgs : EventArgs
        {
            public int intValue { get; set; }

            public NewIntAddEventArgs(int theInt) { intValue = theInt; }
        }

        // this is the EventHandler method that will be available
        // to "subscribe" to by consumers of this class
        public event EventHandler<NewIntAddEventArgs> NewIntAdded;

        public void Add(int newInt)
        {
            // invoke the custom Event
            OnRaiseNewIntAdded(new NewIntAddEventArgs(newInt));

            // let the base internal collection handle the 'Add
            base.Add(newInt);
        }

        // the custom Event code following standard MS C#
        // standards for raising a custom event
        protected virtual void OnRaiseNewIntAdded(NewIntAddEventArgs e)
        {
            EventHandler<NewIntAddEventArgs> handler = NewIntAdded;

            // fire the Event only if there are subscribers !
            if (handler != null) handler(this, e);
        }
    }
}

You might test the notification event facility of this class like this:

//in some Form
CustomIntCollection cIntCollection = new CustomIntCollection();

private void SomeForm_Load(object sender, EventArgs e)
{
    // bind an EventHandler to this instance
    cIntCollection.NewIntAdded += cIntCollection_NewIntAdded;
}

// the EventHandler now bound to the instance of CustomIntCollection:
private void cIntCollection_NewIntAdded(object sender, CustomIntCollection.NewIntAddEventArgs e)
{
    Console.WriteLine("the integer added = " + e.intValue.ToString());
}

// somewhere inside a method in your code
// test adding an int, and range of ints to the instance:
cIntCollection.Add(100);
cIntCollection.AddRange(new List<int>{1,2,3,4});

The code to create custom Events that follows the MS Guidelines (yes, you could do it other ways), and use them, often seems quite strange to new students of C#, but you'll get used to it, and, I believe, you'll realize that what might appear to be a lot of "extra" work is related to allowing:

1. "safety" in code: preventing side-effects

2. creating structures/methods that can be over-ridden in inheriting classes.


[edit]Edit v3 [Nelek] First code block changed from xml to c# to improve color format and readability[/edit]
[edit]Edit v4 [Nelek] Explanation of changes in edit v3 and this line in request of poster[/edit]

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