通过

Control.BackgroundImageChanged 事件

  • 参考

定义

命名空间:
System.Windows.Forms
程序集:
System.Windows.Forms.dll

当 BackgroundImage 属性的值更改时发生。

public:
 event EventHandler ^ BackgroundImageChanged;
public event EventHandler BackgroundImageChanged;
public event EventHandler? BackgroundImageChanged;
member this.BackgroundImageChanged : EventHandler 
Public Custom Event BackgroundImageChanged As EventHandler

事件类型

EventHandler

示例

下面的代码示例是属性值更改时 Text 执行的事件处理程序。 当相应的 PropertyName 值更改 (PropertyName 表示相应属性的名称) 时，该Control类具有多个名称模式 PropertyNameChanged 的方法。

下面的代码示例更改ForeColorTextBox显示货币数据。 本示例将文本转换为十进制数字，并将ForeColorColor.Red数字为负数以及数字为正数时更改为Color.Black。 此示例要求你有一个Form包含 .TextBox

private:
   void currencyTextBox_TextChanged( Object^ /*sender*/, EventArgs^ /*e*/ )
   {
      try
      {
         // Convert the text to a Double and determine if it is a negative number.
         if ( Double::Parse( currencyTextBox->Text ) < 0 )
         {
            // If the number is negative, display it in Red.
            currencyTextBox->ForeColor = Color::Red;
         }
         else
         {
            // If the number is not negative, display it in Black.
            currencyTextBox->ForeColor = Color::Black;
         }
      }
      catch ( Exception^ ) 
      {
         // If there is an error, display the text using the system colors.
         currencyTextBox->ForeColor = SystemColors::ControlText;
      }
   }

private void currencyTextBox_TextChanged(object sender, EventArgs e)
{
   try
   {
      // Convert the text to a Double and determine if it is a negative number.
      if(double.Parse(currencyTextBox.Text) < 0)
      {
         // If the number is negative, display it in Red.
         currencyTextBox.ForeColor = Color.Red;
      }
      else
      {
         // If the number is not negative, display it in Black.
         currencyTextBox.ForeColor = Color.Black;
      }
   }
   catch
   {
      // If there is an error, display the text using the system colors.
      currencyTextBox.ForeColor = SystemColors.ControlText;
   }
}

Private Sub currencyTextBox_TextChanged(sender As Object, _ 
  e As EventArgs) Handles currencyTextBox.TextChanged
   Try
      ' Convert the text to a Double and determine if it is a negative number.
      If Double.Parse(currencyTextBox.Text) < 0 Then
         ' If the number is negative, display it in Red.
         currencyTextBox.ForeColor = Color.Red
      Else
         ' If the number is not negative, display it in Black.
         currencyTextBox.ForeColor = Color.Black
      End If
   Catch
      ' If there is an error, display the text using the system colors.
      currencyTextBox.ForeColor = SystemColors.ControlText
   End Try
End Sub

注解

如果 BackgroundImage 属性通过编程修改或用户交互更改，则会引发此事件。

有关处理事件的详细信息，请参阅 “处理和引发事件”。

适用于

另请参阅