Control.LostFocus 事件

定義

發生於控制項遺失焦點時。Occurs when the control loses focus.

public:
 event EventHandler ^ LostFocus;
[System.ComponentModel.Browsable(false)]
public event EventHandler LostFocus;
member this.LostFocus : EventHandler 
Public Custom Event LostFocus As EventHandler 
屬性

範例

下列程式碼範例示範如何驗證 TextBox1 的文字。The following code example demonstrates validating the text for TextBox1. 它也會示範如何藉由將 FileDialog.InitialDirectory 屬性設定為 TextBox1 中的文字來處理 LostFocus 事件。It also demonstrates handling the LostFocus event by setting the FileDialog.InitialDirectory property to the text in TextBox1. 此程式碼範例使用 ErrorProvider.GetError 方法來檢查是否有錯誤,然後再開啟 [檔案] 對話方塊。The code example used the ErrorProvider.GetError method to check for an error before opening the file dialog box. 若要執行此範例,請將下列程式碼貼入包含名為 TextBox1TextBox、名為 OpenFileDialog1OpenFileDialog、名為 ButtonButton1和名為 ErrorProviderErrorProvider1To run this example, paste the following code into a form containing a TextBox named TextBox1, an OpenFileDialog named OpenFileDialog1, a Button named Button1, and an ErrorProvider named ErrorProvider1. 請確定所有事件都與事件處理常式相關聯。Ensure all events are associated with their event handlers.

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

當您使用鍵盤(TAB、SHIFT + TAB 等等)來變更焦點時,藉由呼叫 SelectSelectNextControl 方法,或是將 ContainerControl.ActiveControl 屬性設定為目前的表單,焦點事件會依照下列順序發生:When you change the focus by using the keyboard (TAB, SHIFT+TAB, and so on), by calling the Select or SelectNextControl methods, or by setting the ContainerControl.ActiveControl property to the current form, focus events occur in the following order:

  1. Enter

  2. GotFocus

  3. Leave

  4. Validating

  5. Validated

  6. LostFocus

當您使用滑鼠或藉由呼叫 Focus 方法來變更焦點時,焦點事件會依照下列順序發生:When you change the focus by using the mouse or by calling the Focus method, focus events occur in the following order:

  1. Enter

  2. GotFocus

  3. LostFocus

  4. Leave

  5. Validating

  6. Validated

如果 CausesValidation 屬性設為 false,則會隱藏 ValidatingValidated 事件。If the CausesValidation property is set to false, the Validating and Validated events are suppressed.

如果在 Validating 事件委派中,CancelEventArgsCancel 屬性設定為 true,則會隱藏在 Validating 事件之後通常會發生的所有事件。If the Cancel property of the CancelEventArgs is set to true in the Validating event delegate, all events that would usually occur after the Validating event are suppressed.

注意

GotFocusLostFocus 事件是與 WM_KILLFOCUS 和 WM_SETFOCUS Windows 訊息系結的低層級焦點事件。The GotFocus and LostFocus events are low-level focus events that are tied to the WM_KILLFOCUS and WM_SETFOCUS Windows messages. 一般而言,只有在更新 UICues 或撰寫自訂控制項時,才會使用 GotFocusLostFocus 事件。Typically, the GotFocus and LostFocus events are only used when updating UICues or when writing custom controls. 相反地,EnterLeave 事件應該用於所有控制項,但不包括使用 ActivatedDeactivate 事件的 Form 類別。Instead the Enter and Leave events should be used for all controls except the Form class, which uses the Activated and Deactivate events. 如需 GotFocusLostFocus 事件的詳細資訊,請參閱WM_KILLFOCUSWM_KILLFOCUS主題。For more information about the GotFocus and LostFocus events, see the WM_KILLFOCUS and WM_KILLFOCUS topics.

警告

請勿嘗試從 EnterGotFocusLeaveLostFocusValidatingValidated 事件處理常式中設定焦點。Do not attempt to set focus from within the Enter, GotFocus, Leave, LostFocus, Validating, or Validated event handlers. 這麼做可能會導致您的應用程式或作業系統停止回應。Doing so can cause your application or the operating system to stop responding. 如需詳細資訊,請參閱WM_KILLFOCUS主題。For more information, see the WM_KILLFOCUS topic.

如需處理事件的詳細資訊,請參閱處理和引發事件For more information about handling events, see Handling and Raising Events.

適用於

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