Control.LostFocus 事件

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

來源:

Control.cs

當控制失焦時會發生。

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 

事件類型

EventHandler

屬性

BrowsableAttribute

範例

以下程式碼範例示範如何驗證 TextBox1 的文字。 它也示範如何處理 LostFocus 事件，方法是將屬性設定 FileDialog.InitialDirectory 為 TextBox1 中的文字。 程式碼範例使用該 ErrorProvider.GetError 方法在開啟檔案對話框前檢查錯誤。 要執行此範例，將以下程式碼貼入包含 TextBox 、 、 OpenFileDialogOpenFileDialog1、 ButtonButton1ErrorProvider 和 。ErrorProvider1TextBox1 確保所有事件都與其事件處理者相關聯。

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

備註

當你用鍵盤（TAB、SHIFT+TAB 等）、呼叫 Select or SelectNextControl 方法，或將屬性設 ContainerControl.ActiveControl 為當前形式來更改焦點時，焦點事件會依以下順序發生：

1. Enter

2. GotFocus

3. Leave

4. Validating

5. Validated

6. LostFocus

當你用滑鼠或呼叫 Focus 方法改變焦點時，焦點事件會依以下順序發生：

1. Enter

2. GotFocus

3. LostFocus

4. Leave

5. Validating

6. Validated

若 CausesValidation 屬性設為 false，則 Validating 與 Validated 事件會被抑制。

如果 Cancel 的 CancelEventArgs 屬性設定為 true 事件委托中 Validating ，所有通常會在事件後 Validating 發生的事件都會被抑制。

備註

和GotFocusLostFocus事件是低階焦點事件，與 WM_KILLFOCUS 和 WM_SETFOCUS Windows 訊息相關聯。 通常， GotFocus 和 LostFocus 事件僅在更新 UICues 或撰寫自訂控制時使用。 相反地Enter，除了類別外，所有控制ActivatedForm都應該使用 and LeaveDeactivate 事件。 欲了解更多相關 GotFocus 資訊及 LostFocus 活動資訊，請參閱 WM_KILLFOCUS 及 WM_KILLFOCUS 主題。

謹慎

不要試圖從 、 GotFocus、 Leave、 LostFocusValidatingValidated 、 或事件處理者中Enter來設定焦點。 這樣做可能會導致你的應用程式或作業系統停止回應。 欲了解更多資訊，請參閱 WM_KILLFOCUS 主題。

如需處理事件的詳細資訊，請參閱 處理和引發事件。

另請參閱

• OnLostFocus(EventArgs)
• GotFocus
• Leave
• Deactivate