如何订阅Form的自定义事件

2019-11-14 13:42:41

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　　Window Form类有很多的属性/方法和事件,其中事件属于一种发布订阅模式。订阅发布模式定义了一种一对多的依赖关系，让多个订阅者对象同时监听某一个主体对象。这个主体对象在自身状态变化时，会通知所有订阅者对象，使它们能够自动更新自己的状态。当一个对象的改变需要同时改变其他对象，而且无需关心具体有多少对象需要改变时，就特别适合用此种模式。本文将演示如何在窗体上自定义一个事件(custom event) :

1 自定义一个CustomEventArgs类

　　一般自定义的事件都有一个参数,继承自EventArgs.此处我们自定一个CustomEventArgs,类中通过自定义字段来存储参数的值:

 1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5  6 namespace CustomEventsDemo 7 { 8     public class CustomEventArgs:EventArgs 9     {10         //自定义字段用于存储值11         public object Tag;12         public string Message;13         public CustomEventArgs()14         {15             16         }17         public CustomEventArgs(string message, object tag)18         {19             Message = message;20             Tag = tag;21         }22     }23 }

2 自定义一个事件

　　接下来我们创建一个FormPublisher窗体,然后用 event EventHandler<CustomEventArgs> customEvent;event EventHandler<CustomEventArgs> customSecondEvent和来自定义两个custom Event事件,它们的事件参数为CustomEventArgs.在窗体加载事件中我们触发两个事件(这个顺序会影响在窗体加载时订阅者的事件响应顺序.如果我们创建一个窗体继承此FormPublisher的话,我们会在此窗体的事件面板中看到下图:

 1 using System; 2 using System.Collections.Generic; 3 using System.ComponentModel; 4 using System.Data; 5 using System.Drawing; 6 using System.Linq; 7 using System.Text; 8 using System.Windows.Forms; 9 10 namespace CustomEventsDemo11 {12     public partial class FormPublisher : Form13     {14         //定义两个事件15         public event EventHandler<CustomEventArgs> customEvent;16         public event EventHandler<CustomEventArgs> customSecondEvent;17         public FormPublisher()18         {19             InitializeComponent();20         }21 22         PRivate void FormWithCutomEvent_Load(object sender, EventArgs e)23         {24             //确定自定义事件的执行顺序,继承此窗体的子类窗体加载时的默认顺序25             if (customEvent != null)26             {27                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");28                 customEvent(this, customEventArgs);29             }30             if (customSecondEvent != null)31             {32 33                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");34                 customSecondEvent(this, customEventArgs);35             }36 37         }38 39         private void button1_Click(object sender, EventArgs e)40         {41             42             this.textBox2.AppendText(this.textBox1.Text + "/r/n");43             //this.textBox1.Text = "";44             if (customSecondEvent != null)45             {46                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");47                 //触发事件48                 customSecondEvent(this, customEventArgs);49             }50             if (customEvent != null)51             {52                 CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");53                 //触发事件54                 customEvent(this, customEventArgs);55             }56         }57     }58 }

3 订阅事件

　　下面定义一个FormSubscriber窗体来订阅自定义事件,我们要定义另一个窗体的事件,必须要先实例化那个窗体,否则会调用失败:

 1 using System; 2 using System.Collections.Generic; 3 using System.ComponentModel; 4 using System.Data; 5 using System.Drawing; 6 using System.Linq; 7 using System.Text; 8 using System.Windows.Forms; 9 10 namespace CustomEventsDemo11 {12     public partial class FormSubscriber : Form13     {14         FormPublisher form = null;15        public FormSubscriber()16         {17             InitializeComponent();18             //启动2个窗体19             form = new FormPublisher();20             form.Visible = true;21            //订阅事件22             form.customSecondEvent += form_customSecondEvent;23            //订阅事件24             form.customEvent += form_customEvent;25            //把发布窗体实例化后传入第二个订阅窗体中,否则不能订阅26             FormSubScriber2 from2 = new FormSubScriber2(form);27             from2.Visible = true;28         }29 30        void form_customSecondEvent(object sender, CustomEventArgs e)31        {32            this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "/r/n");33        }34 35        void form_customEvent(object sender, CustomEventArgs e)36        {37            this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "/r/n");38        }39 40         private void FormSubscriber_Load(object sender, EventArgs e)41         {42             43         }44     }45 }

　　另一个窗体也进行订阅:

 1 using System; 2 using System.Collections.Generic; 3 using System.ComponentModel; 4 using System.Data; 5 using System.Drawing; 6 using System.Linq; 7 using System.Text; 8 using System.Windows.Forms; 9 10 namespace CustomEventsDemo11 {12     public partial class FormSubScriber2 : Form13     {14      15         public FormSubScriber2()16         {17             InitializeComponent();18         }19         public FormSubScriber2(FormPublisher form)20         {21             InitializeComponent();22             //订阅form自定义事件23             form.customEvent += form_customEvent;24         }25         void form_customEvent(object sender, CustomEventArgs e)26         {27             this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "/r/n");28         }29 30         private void FormSubScriber2_Load(object sender, EventArgs e)31         {32 33         }34     }35 }