[C#]RaiseEvent Extension Method (二)

前面[C#]RaiseEvent Extension Method (一)這篇介紹了如何用擴充方法來簡化C#事件的觸發動作,最近在做觸發事件時,又看到了一個引起我關注的重點,那就是有時候我們在初始化事件的參數時費了很大的耗費,準備觸發事件時,透過OnXXX去觸發事件,結果發現事件並未被繫上,整個事件觸發的動作就不做了,那麼前面所作的參數準備不就是不必要的耗費?


Var e = new MyEventArgs() {…};

OnMyEvent(e);


當然這樣的問題可以在觸發事件的地方用if判別去避開,但這樣就會讓程式在維護與閱讀上的困難度上升,筆者在[.Net Concept]理解事件的宣告方式與用法這篇有對此做詳細的描述,這邊不多做解釋。

因為有上面的原因,筆者又花了一點時間將擴充方法做了些改進,增加兩個多載版本,使其能帶入初始化事件參數的方法,如此在事件未繫上時就不會做初始的動作。

    public static class ObjectExtension
{
public static void RaiseEvent(this object obj, EventHandler handler, EventArgs e)
{
RaiseEvent(obj, handler, () => e);
}

public static void RaiseEvent(this object obj, EventHandler handler, Func<EventArgs> func)
{
if (handler == null)
return;
handler(obj, func());
}

public static void RaiseEvent<TEventArgs>(this object obj, EventHandler<TEventArgs> handler, TEventArgs e) where TEventArgs : EventArgs
{
RaiseEvent(obj, handler, () => e);
}

public static void RaiseEvent<TEventArgs>(this object obj, EventHandler<TEventArgs> handler,Func<TEventArgs> func) where TEventArgs : EventArgs
{
if (handler == null)
return;
handler(obj, func());
}
}

使用上透過Lambda的輔助也十分的好上手。

this.RaiseEvent(MyEvent, () => new MyEventArgs()
{
//Init EventArgs

});

完整的範例程式如下:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication14
{
class Program
{
static void Main(string[] args)
{
Person Larry = new Person();
Larry.NameChanged += new EventHandler<NameEventArgs>(Larry_NameChanged);
Larry.Name = “Larry”;
}
static void Larry_NameChanged(object sender, NameEventArgs e)
{
Console.WriteLine(string.Format(“NameChanged to {0}”, e.Name));
}
}
public static class ObjectExtension
{
public static void RaiseEvent(this object obj, EventHandler handler, EventArgs e)
{
RaiseEvent(obj, handler, () => e);
}

public static void RaiseEvent(this object obj, EventHandler handler, Func<EventArgs> func)
{
if (handler == null)
return;
handler(obj, func());
}

public static void RaiseEvent<TEventArgs>(this object obj, EventHandler<TEventArgs> handler, TEventArgs e) where TEventArgs : EventArgs
{
RaiseEvent(obj, handler, () => e);
}

public static void RaiseEvent<TEventArgs>(this object obj, EventHandler<TEventArgs> handler,Func<TEventArgs> func) where TEventArgs : EventArgs
{
if (handler == null)
return;
handler(obj, func());
}
}

class NameEventArgs : EventArgs
{
public string Name { get; set; }
}

class Person
{
private string _name;
public string Name
{
get
{
if (_name == null)
return string.Empty;
return _name;
}
set
{
if (_name != value)
{
_name = value;
this.RaiseEvent(NameChanged, () => new NameEventArgs() { Name = value });
}
}
}
public event EventHandler<NameEventArgs> NameChanged;
}

}

運行的結果如下:

image