Control.LostFocus 事件

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

Source:

Control.cs

当控件失去焦点时发生。

public:
 event EventHandler ^ LostFocus;

[System.ComponentModel.Browsable(false)]
public event EventHandler? LostFocus;

[<System.ComponentModel.Browsable(false)>]
member this.LostFocus : EventHandler 

Public Custom Event LostFocus As EventHandler 

事件类型

EventHandler

属性

BrowsableAttribute

示例

下面的代码示例演示如何验证 TextBox1 的文本。 它还演示 LostFocus 了通过将属性设置为 FileDialog.InitialDirectory TextBox1 中的文本来处理事件。 代码示例使用 ErrorProvider.GetError 该方法在打开文件对话框之前检查错误。 若要运行此示例，请将以下代码粘贴到包含TextBox命名、OpenFileDialog命名TextBox1、命名OpenFileDialog1Button1Button和命名ErrorProvider1的ErrorProvider窗体中。 确保所有事件都与其事件处理程序相关联。

private:
   void TextBox1_Validating( Object^ sender,
      System::ComponentModel::CancelEventArgs^ e )
   {
      // If nothing is entered,
      // an ArgumentException is caught; if an invalid directory is entered, 
      // a DirectoryNotFoundException is caught. An appropriate error message 
      // is displayed in either case.
      try
      {
         System::IO::DirectoryInfo^ directory = gcnew System::IO::DirectoryInfo( TextBox1->Text );
         directory->GetFiles();
         ErrorProvider1->SetError( TextBox1, "" );
      }
      catch ( System::ArgumentException^ ) 
      {
         ErrorProvider1->SetError( TextBox1, "Please enter a directory" );
      }
      catch ( System::IO::DirectoryNotFoundException^ ) 
      {
         ErrorProvider1->SetError( TextBox1, "The directory does not exist."
         "Try again with a different directory." );
      }
   }

   // This method handles the LostFocus event for TextBox1 by setting the 
   // dialog's InitialDirectory property to the text in TextBox1.
   void TextBox1_LostFocus( Object^ sender, System::EventArgs^ e )
   {
      OpenFileDialog1->InitialDirectory = TextBox1->Text;
   }

   // This method demonstrates using the ErrorProvider.GetError method 
   // to check for an error before opening the dialog box.
   void Button1_Click( System::Object^ sender, System::EventArgs^ e )
   {
      //If there is no error, then open the dialog box.
      if ( ErrorProvider1->GetError( TextBox1 )->Equals( "" ) )
      {
         ::DialogResult dialogResult = OpenFileDialog1->ShowDialog();
      }
   }

private void textBox1_Validating(object sender, 
    System.ComponentModel.CancelEventArgs e)
{
    // If nothing is entered,
    // an ArgumentException is caught; if an invalid directory is entered, 
    // a DirectoryNotFoundException is caught. An appropriate error message 
    // is displayed in either case.
    try
    {
        System.IO.DirectoryInfo directory = 
            new System.IO.DirectoryInfo(textBox1.Text);
        directory.GetFiles();
        errorProvider1.SetError(textBox1, "");
    }
    catch(System.ArgumentException ex1)
    {
        errorProvider1.SetError(textBox1, "Please enter a directory");
    }
    catch(System.IO.DirectoryNotFoundException ex2)
    {
        errorProvider1.SetError(textBox1, "The directory does not exist." +
            "Try again with a different directory.");
    }
}

// This method handles the LostFocus event for textBox1 by setting the 
// dialog's InitialDirectory property to the text in textBox1.
private void textBox1_LostFocus(object sender, System.EventArgs e)
{
    openFileDialog1.InitialDirectory = textBox1.Text;
}

// This method demonstrates using the ErrorProvider.GetError method 
// to check for an error before opening the dialog box.
private void button1_Click(System.Object sender, System.EventArgs e)
{
    //If there is no error, then open the dialog box.
    if (errorProvider1.GetError(textBox1)=="")
    {
        DialogResult dialogResult = openFileDialog1.ShowDialog();
    }
}

Private Sub TextBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
Handles TextBox1.Validating

    ' If nothing is entered,
    ' an ArgumentException is caught; if an invalid directory is entered, 
    ' a DirectoryNotFoundException is caught. An appropriate error message 
    ' is displayed in either case.
    Try
        Dim directory As New System.IO.DirectoryInfo(TextBox1.Text)
        directory.GetFiles()
        ErrorProvider1.SetError(TextBox1, "")

    Catch ex1 As System.ArgumentException
        ErrorProvider1.SetError(TextBox1, "Please enter a directory")

    Catch ex2 As System.IO.DirectoryNotFoundException
        ErrorProvider1.SetError(TextBox1, _
        "The directory does not exist." & _
        "Try again with a different directory.")
    End Try

End Sub

' This method handles the LostFocus event for TextBox1 by setting the 
' dialog's InitialDirectory property to the text in TextBox1.
Private Sub TextBox1_LostFocus(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles TextBox1.LostFocus
    OpenFileDialog1.InitialDirectory = TextBox1.Text
End Sub


' This method demonstrates using the ErrorProvider.GetError method 
' to check for an error before opening the dialog box.
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

    'If there is no error, then open the dialog box.
    If ErrorProvider1.GetError(TextBox1) = "" Then
        Dim dialogResult As DialogResult = OpenFileDialog1.ShowDialog()
    End If

End Sub

注解

使用键盘（TAB、SHIFT+TAB 等）更改焦点时，通过调用 Select 或 SelectNextControl 方法，或通过将 ContainerControl.ActiveControl 属性设置为当前窗体来更改焦点时，焦点事件按以下顺序发生：

1. Enter

2. GotFocus

3. Leave

4. Validating

5. Validated

6. LostFocus

使用鼠标或调用 Focus 方法更改焦点时，焦点事件按以下顺序发生：

1. Enter

2. GotFocus

3. LostFocus

4. Leave

5. Validating

6. Validated

CausesValidation如果该属性设置为false，则Validating取消该属性和Validated事件。

如果事件Cancel委托中的CancelEventArgs属性true设置为Validating事件委托，则会禁止显示事件后Validating通常会发生的所有事件。

注释

事件GotFocusLostFocus是与WM_KILLFOCUS和WM_SETFOCUS Windows 消息绑定的低级别焦点事件。 通常，GotFocus仅当更新UICues或编写自定义控件时，才会使用和LostFocus事件。 Enter应将和Leave事件用于除使用Activated和Deactivate事件的类以外的Form所有控件。 有关和LostFocus事件的详细信息GotFocus，请参阅WM_KILLFOCUS和WM_KILLFOCUS主题。

注意

请勿尝试从内部Enter、GotFocus、Leave、LostFocus或ValidatingValidated事件处理程序设置焦点。 这样做可能会导致应用程序或操作系统停止响应。 有关详细信息，请参阅 WM_KILLFOCUS 主题。

有关处理事件的详细信息，请参阅 处理和引发事件。

另请参阅

• OnLostFocus(EventArgs)
• GotFocus
• Leave
• Deactivate