如何在控件實例化後立即發送自定義事件消息？

Question

我有零異常錯誤創建此自定義控件時發送的ValueChanged（）事件，並測試它在客戶端：然後在測試形式

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

namespace customevent 
{ 
    [DefaultEvent("ValueChanged")] 
    public partial class UserControl1 : UserControl 
    { 
     private int m_value; 

     public delegate void ValueChangedHandler(); 
     [Category("Action")] 
     [Description("Value changed.")] 
     public event ValueChangedHandler ValueChanged; 

     public int Value 
     { 
      get { return m_value; } 
      set { 
       m_value = value; 
       ValueChanged(); 
      } 
     } 

     public UserControl1() 
     { 
      InitializeComponent(); 
     } 
     public UserControl1(int iValue) 
     { 
      this.Value = iValue; 
      InitializeComponent(); 
     } 

    } 
} 

：

自定義控件的來源

private void Form1_Load(object sender, EventArgs e) 
    { 
     userControl11.Value = 100; 
    } 

    private void userControl11_ValueChanged() 
    { 
     MessageBox.Show(userControl11.Value.ToString()); 
    } 

或代替的Form_Load，在構造函數中做到這一點：

private void InitializeComponent() 
    { 
     this.userControl11 = new customevent.UserControl1(100); 

Answer 1

你不檢查NULL值：

public int Value 
    { 
     get { return m_value; } 
     set { 
      m_value = value; 
      if(ValueChanged != null) 
      { 
       ValueChanged(); 
      } 
     } 
    } 

此外，你還沒有掛鉤到這個事件在您的形式：

private void Form1_Load(object sender, EventArgs e) 
{ 
    userControl1.ValueChanged += userControl11_ValueChanged; 
    userControl11.Value = 100; 
} 

private void userControl11_ValueChanged() 
{ 
    MessageBox.Show(userControl11.Value.ToString()); 
} 

Answer 2

您應該聲明事件處理，因爲這：

public event EventHandler ValueChanged; 

protected virtual void OnValueChanged(object sender, EventArgs e) 
{ 
    if (ValueChanged != null) 
    { 
     ValueChanged(sender, e); 
    } 
} 

public int Value 
{ 
    get { return m_value; } 
    set { 
     if (m_value == value) return; 
     m_value = value; 
     OnValueChanged(this, EventArgs.Empty); 
    } 
} 

PS：有一個接口INotifyPropertyChanged，你應該用它來符合標準的.NET數據綁定規則。

Answer 3

西蒙得你幾乎有：

protected virtual void OnValueChanged(object sender, EventArgs e) 
{ 
    var tmp = ValueChanged; 
    if (tmp != null) 
    { 
     tmp(sender, e); // With the tmp, we won't explode if a subscriber changes the collection of delegates underneath us. 
    } 
}