C#委托与事件机制详解-优快云博客

csdn学生大本营关掉啦俺赶快转blog啊..

今天猫难得得空了一天呀于是翻开c#本质论又看了章;;

要看事件先来看看多播委托呐

上次俺已写了篇再看委托的笔记小提了下窗体间用委托进行刷新的方法

多播委托:一个委托变量可以引用一系列委托,在这一系列委托中,每个委托都顺序指向一个后续的委托,从而形成了一个委托链

说白了就是给一个委托变量绑定多个方法名..

拿上次那个窗体来讲我改了一下代码

有两个窗体我要在第二个窗体里改变第一个窗体里几个TextBox的Text属性我把修改每一个Text的属性都写在了一个方法中并将它们赋值给了另一个窗体的相应的委托

form1代码

Code:

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
Form2 f2=new Form2();
f2.RefreshTest += RefreshTextBox1;
f2.RefreshTest += RefreshTextBox2;
f2.RefreshTest += RefreshTextBox3;
f2.ShowDialog();
}
public void RefreshTextBox1()
{
this.textBox1.Text = "Catsoul!";
}
public void RefreshTextBox2()
{
this.textBox2.Text = "Monsoul!";
}
public void RefreshTextBox3()
{
this.textBox3.Text = "Catsoul love Monsoul forever!";
}
}

form2代码

Code:

public partial class Form2 : Form
{
public delegate void RefreshData();
public RefreshData RefreshTest { get; set; }
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
this.RefreshTest();
}
private void Form2_Load(object sender, EventArgs e)
{
}
}

结果是这样滴:

主要是这段代码

Code:

Form2 f2=new Form2();
f2.RefreshTest += RefreshTextBox1;
f2.RefreshTest += RefreshTextBox2;
f2.RefreshTest += RefreshTextBox3;
f2.ShowDialog();

我实例化了一个Form2窗体并给它的RefreshTest委托添加了三个方法

用+=向RefreshTest委托添加(注册)了三个方法(订阅者)

上次我说过观察者模式理解成被观察者通知观察者其实这里就叫发布者向订阅者通知消息

可以通过-=从委托链中中删除委托而且可以通过+和-与合并,清除委托就是委托支持+= -= + - = 等运算符从字面上就能理解出这些玩意功能了.!

多播委托有很多地方存在一些隐患

第一我们很容易把+=写成=!

比如那个窗体里的代码我们很容易写成这样!

Code:

f2.RefreshTest = RefreshTextBox1;
f2.RefreshTest = RefreshTextBox2;
f2.RefreshTest = RefreshTextBox3;

这样我们最后只能执行RefreshTextBox3()这个方法了!

第二空值问题

如果我们没有给RefreshTest委托添加方法时,咱们调用它,就会出现异常!

提示引用对象米有实例!

第三异常问题

假如委托链中一个方法引发了异常链中后续的方法就不会执行了

由此我们要这么写它的代码

Code:

//遍历委托链
foreach (RefreshData refreshData in this.RefreshTest.GetInvocationList())
{
try
{
refreshData();
}
catch (Exception)
{
throw;
}
}

咱们必须遍历它的委托链,把异常捕捉掉! 这样才能保证它能完整地执行完!

第四方法返回值和传引用

所有方法都必须使用与委托相同的方法签名如果每个方法都都要返回一个值这里就出现了问题!

所以这里我们必须像刚刚那个异常处理一样遍历委托链获取每个单独的返回值

ref和out也是一样的道理!

对于这里里面的几个缺陷使用事件可以解决两个问题!

先撇开事件的编程规范来写一个简易事件!

首先我把Form2代码改了一行! 对, 就一行!

Code:

public partial class Form2 : Form
{
public delegate void RefreshData();
// public RefreshData RefreshTest { get; set; }
public event RefreshData RefreshTest = delegate { };
public Form2()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
this.RefreshTest();
}
private void Form2_Load(object sender, EventArgs e)
{
}
}

我把原委托属性改成了一个事件

这里不用担心直接设为public而破坏了封装 ! 请往下看!

咱们来看看CIL对应的c#代码

Code:

public class Form2 : Form
{
// Fields
private Button button1;
private IContainer components = null;
这里!
----------------------------------------------------------
private RefreshData RefreshTest = delegate {
};
------------------------------------------------------------
下面也是重点!注意add和remove!
// Events
public event RefreshData RefreshTest
{
add
{
RefreshData data2;
RefreshData refreshTest = this.RefreshTest;
do
{
data2 = refreshTest;
RefreshData data3 = (RefreshData) Delegate.Combine(data2, value);
refreshTest = Interlocked.CompareExchange<RefreshData>(ref this.RefreshTest, data3, data2);
}
while (refreshTest != data2);
}
remove
{
RefreshData data2;
RefreshData refreshTest = this.RefreshTest;
do
{
data2 = refreshTest;
RefreshData data3 = (RefreshData) Delegate.Remove(data2, value);
refreshTest = Interlocked.CompareExchange<RefreshData>(ref this.RefreshTest, data3, data2);
}
while (refreshTest != data2);
}
}
// Methods
public Form2()
{
this.InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
this.RefreshTest();
}
protected override void Dispose(bool disposing)
{
if (disposing && (this.components != null))
{
this.components.Dispose();
}
base.Dispose(disposing);
}
private void Form2_Load(object sender, EventArgs e)
{
}
private void InitializeComponent()
{
this.button1 = new Button();
base.SuspendLayout();
this.button1.Location = new Point(0x6a, 0x84);
this.button1.Name = "button1";
this.button1.Size = new Size(0x4b, 0x17);
this.button1.TabIndex = 0;
this.button1.Text = "button1";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new EventHandler(this.button1_Click);
base.AutoScaleDimensions = new SizeF(6f, 13f);
base.AutoScaleMode = AutoScaleMode.Font;
base.ClientSize = new Size(0x11c, 0x106);
base.Controls.Add(this.button1);
base.Name = "Form2";
this.Text = "Form2";
base.Load += new EventHandler(this.Form2_Load);
base.ResumeLayout(false);
}
// Nested Types
public delegate void RefreshData();
}