如何订阅Form的自定义事件

 　　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:

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

namespace CustomEventsDemo
{
    public class CustomEventArgs:EventArgs
    {
        //自定义字段用于存储值
        public object Tag;
        public string Message;
        public CustomEventArgs()
        {
            
        }
        public CustomEventArgs(string message, object tag)
        {
            Message = message;
            Tag = tag;
        }
    }
}

 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:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomEventsDemo
{
    public partial class FormPublisher : Form
    {
        //定义两个事件
        public event EventHandler<CustomEventArgs> customEvent;
        public event EventHandler<CustomEventArgs> customSecondEvent;
        public FormPublisher()
        {
            InitializeComponent();
        }

        private void FormWithCutomEvent_Load(object sender, EventArgs e)
        {
            //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
            if (customEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
                customEvent(this, customEventArgs);
            }
            if (customSecondEvent != null)
            {

                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
                customSecondEvent(this, customEventArgs);
            }

        }

        private void button1_Click(object sender, EventArgs e)
        {
            
            this.textBox2.AppendText(this.textBox1.Text + "
");
            //this.textBox1.Text = "";
            if (customSecondEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customSecondEvent");
                //触发事件
                customSecondEvent(this, customEventArgs);
            }
            if (customEvent != null)
            {
                CustomEventArgs customEventArgs = new CustomEventArgs(this.textBox1.Text, "customEvent");
                //触发事件
                customEvent(this, customEventArgs);
            }
        }
    }
}

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:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomEventsDemo
{
    public partial class FormSubscriber : Form
    {
        FormPublisher form = null;
       public FormSubscriber()
        {
            InitializeComponent();
            //启动2个窗体
            form = new FormPublisher();
            form.Visible = true;
           //订阅事件
            form.customSecondEvent += form_customSecondEvent;
           //订阅事件
            form.customEvent += form_customEvent;
           //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
            FormSubScriber2 from2 = new FormSubScriber2(form);
            from2.Visible = true;
        }

       void form_customSecondEvent(object sender, CustomEventArgs e)
       {
           this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "
");
       }

       void form_customEvent(object sender, CustomEventArgs e)
       {
           this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "
");
       }

        private void FormSubscriber_Load(object sender, EventArgs e)
        {
            
        }
    }
}

 　　另一个窗体也进行订阅:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomEventsDemo
{
    public partial class FormSubScriber2 : Form
    {
     
        public FormSubScriber2()
        {
            InitializeComponent();
        }
        public FormSubScriber2(FormPublisher form)
        {
            InitializeComponent();
            //订阅form自定义事件
            form.customEvent += form_customEvent;
        }
        void form_customEvent(object sender, CustomEventArgs e)
        {
            this.textBox1.AppendText("Message from Publisher " + e.Message + " from " + e.Tag + "
");
        }

        private void FormSubScriber2_Load(object sender, EventArgs e)
        {

        }
    }
}