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法學.NET中的事件模式是如何工作的？
事件是一種使用委託的簡化模式。在C#中，所有委託都具有多播能力，即委託的例項不僅可以表示單個方法，還可以表示方法列表。例如：
示例
delegate int Transformer(int x);
static void Main(){
Transformer perform = x =>{
int result = x * x;
Console.WriteLine(result);
return result;
};
perform += x =>{
int result = x * x * x;
Console.WriteLine(result);
return result;
};
perform(2); // prints 4 and 8
}呼叫Perform()會呼叫新增到委託中的所有方法。方法按照新增的順序呼叫。
這允許你實現釋出-訂閱模式，也稱為事件模式。釋出者包含一個委託欄位。它決定何時透過呼叫委託來發布。訂閱者將自己的方法新增到釋出者的委託中，因此每當釋出者決定透過呼叫委託來發布時，它們都會收到通知。訂閱者不知道也不干涉其他訂閱者。
C#事件是一種語言特性，它以型別安全的方式規範了上述模式，從而避免了委託的常見錯誤。事件公開實現事件模式所需的委託功能的子集。下面的示例對此進行了說明。
首先，定義事件發生時要傳送的資料結構。
public class ThresholdReachedEventArgs : EventArgs{
public int Threshold { get; set; }
public DateTime TimeReached { get; set; }
}然後，定義釋出者，即想要引發事件的類。
public class Counter{
// 1. Define an event
public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
// 2. Do something that raises the event, and pass the EventArgs custom data
public void DoSomething(){
ThresholdReachedEventArgs e = new ThresholdReachedEventArgs{
Threshold = 10,
TimeReached = DateTime.Now
};
// 3. Raise the actual event
ThresholdReached?.Invoke(this, e);
}
}最後，建立一個或多個訂閱者。想要監聽釋出者引發的事件的類。
class Program{
static void Main(string[] args){
// 1. Create an instance of the publisher, which you want to listen to
Counter counter = new Counter();
// 2. Attach an event handler on the publisher
counter.ThresholdReached += OnThresholdReached;
// 3. Do something that will raise the event. Now you are ready to listen to the event.
counter.DoSomething();
}
// 4. Handle the event which is raised by publisher
static void OnThresholdReached(object sender, ThresholdReachedEventArgs e){
Console.WriteLine($"Reached Threshold {e.Threshold} at {e.TimeReached.ToString()}");
}
}示例
using System;
class Program{
static void Main(string[] args){
// 1. Create an instance of the publisher, which you want to listen to
Counter counter = new Counter();
// 2. Attach an event handler on the publisher
counter.ThresholdReached += OnThresholdReached;
// 3. Do something that will raise the event. Now you are ready to listen to the event.
counter.DoSomething();
}
// 4. Handle the event which is raised by publisher
static void OnThresholdReached(object sender, ThresholdReachedEventArgs e){
Console.WriteLine($"Reached Threshold {e.Threshold} at {e.TimeReached.ToString()}");
}
}
public class ThresholdReachedEventArgs : EventArgs{
public int Threshold { get; set; }
public DateTime TimeReached { get; set; }
}
public class Counter{
// 1. Define an event
public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
// 2. Do something that raises the event, and pass the EventArgs custom data
public void DoSomething(){
ThresholdReachedEventArgs e = new ThresholdReachedEventArgs{
Threshold = 10,
TimeReached = DateTime.Now
};
// 3. Raise the actual event
ThresholdReached?.Invoke(this, e);
}
}輸出
Reached Threshold 10 at 5/15/2021 12:49:10 PM
更新於：2021年5月19日
475 次瀏覽
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