Control.LostFocus 事件

项目
08/17/2007

当控件失去焦点时发生。

**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）

语法

声明
Public Event LostFocus As EventHandler
用法
Dim instance As Control
Dim handler As EventHandler

AddHandler instance.LostFocus, handler

public event EventHandler LostFocus

public:
event EventHandler^ LostFocus {
    void add (EventHandler^ value);
    void remove (EventHandler^ value);
}

/** @event */
public void add_LostFocus (EventHandler value)

/** @event */
public void remove_LostFocus (EventHandler value)

JScript 支持使用事件，但不支持进行新的声明。

备注

当通过使用键盘（Tab、Shift+Tab 等）、通过调用 Select 或 SelectNextControl 方法或者通过将 ContainerControl.ActiveControl 属性设置为当前窗体等方式更改焦点时，焦点事件按以下顺序发生：

当通过使用鼠标或调用 Focus 方法的方式更改焦点时，焦点事件按以下顺序发生：

Enter
GotFocus
LostFocus
Leave
Validating
Validated

如果 CausesValidation 属性设置为 false，则将取消 Validating 和 Validated 事件。

如果在 Validating 事件委托中，CancelEventArgs 的 Cancel 属性设置为 true，则正常情况下将在 Validating 事件之后发生的所有事件均被取消。

提示

GotFocus 和 LostFocus 事件是关联于 WM_KILLFOCUS 和 WM_SETFOCUS Windows 消息的低级别焦点事件。通常，GotFocus 和 LostFocus 事件仅在更新 UICues 或编写自定义控件时使用。而 Enter 和 Leave 事件应该用于除 Form 类（该类使用 Activated 和 Deactivate 事件）之外的所有控件。有关 GotFocus 和 LostFocus 事件的更多信息，请参见 MSDN Library（位于 https://www.microsoft.com/china/msdn/library. Platform SDK 文档的“Keyboard Input Reference”（键盘输入参考）部分中的 WM_SETFOCUS 和 WM_KILLFOCUS 主题。

警告

请勿尝试从 LostFocus 事件处理程序中设置焦点。这样操作可能导致应用程序或操作系统停止响应。有关 LostFocus 事件的更多信息，请参见 MSDN Library（位于 https://www.microsoft.com/china/msdn/library. Platform SDK 文档的“Keyboard Input Reference”（键盘输入参考）部分中的 WM_KILLFOCUS 主题以及“Messages and Message Queues”（消息和消息队列）部分中的 Message Deadlocks 主题。

有关处理事件的更多信息，请参见使用事件。

示例

下面的代码示例演示如何验证 TextBox1 的文本。它还演示如何通过将 FileDialog.InitialDirectory 属性设置为 TextBox1 中的文本来处理 LostFocus 事件。该代码示例在打开文件对话框之前，使用 ErrorProvider.GetError 方法检查错误。若要运行此示例，请将下面的代码粘贴到一个窗体中，该窗体包含一个名为 TextBox1 的 TextBox、一个名为 OpenFileDialog1 的 OpenFileDialog、一个名为 Button1 的 Button 以及一个名为 ErrorProvider1 的 ErrorProvider。确保所有事件都与其事件处理程序关联。

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

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:
   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.get_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.");
    }
} //textBox1_Validating

// 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.set_InitialDirectory(textBox1.get_Text());
} //textBox1_LostFocus

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

平台

Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition

.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。

版本信息

.NET Framework

受以下版本支持：2.0、1.1、1.0

.NET Compact Framework

受以下版本支持：2.0、1.0

请参见

参考

Control 类
 Control 成员
 System.Windows.Forms 命名空间
 OnLostFocus
Control.GotFocus 事件
 Control.Leave 事件
 Form.Deactivate

Control.LostFocus 事件

语法

备注

示例

平台

版本信息

.NET Framework

.NET Compact Framework

请参见

参考

其他资源