Form.KeyPreview Form.KeyPreview Form.KeyPreview Form.KeyPreview Property

Определение

Возвращает или задает значение, указывающее, получит ли форма события клавиш перед передачей событий элементу управления, на который установлен фокус.Gets or sets a value indicating whether the form will receive key events before the event is passed to the control that has focus.

public:
 property bool KeyPreview { bool get(); void set(bool value); };
public bool KeyPreview { get; set; }
member this.KeyPreview : bool with get, set
Public Property KeyPreview As Boolean

Значение свойства

Значение true, если форма получит все события клавиш; значение false, если выбранный в настоящее время элемент управления в форме получает события клавиш.true if the form will receive all key events; false if the currently selected control on the form receives key events. Значение по умолчанию — false.The default is false.

Примеры

В следующем примере демонстрируется установка свойства формы KeyPreview в значение true и обработка ключевых событий на уровне формы.The following example demonstrates setting a form's KeyPreview property to true and handling the key events at the form level. Чтобы выполнить пример, вставьте следующий код в пустую форму.To run the example, paste the following code in a blank form.

using namespace System::Windows::Forms;

// This button is a simple extension of the button class that overrides
// the ProcessMnemonic method.  If the mnemonic is correctly entered,  
// the message box will appear and the click event will be raised.  
// This method makes sure the control is selectable and the 
// mnemonic is correct before displaying the message box
// and triggering the click event.
public ref class MyMnemonicButton: public Button
{
protected:
   bool ProcessMnemonic( char inputChar )
   {
      if ( CanSelect && IsMnemonic( inputChar, this->Text ) )
      {
         MessageBox::Show( "You've raised the click event "
         "using the mnemonic." );
         this->PerformClick();
         return true;
      }

      return false;
   }

};


// Declare the controls contained on the form.
public ref class Form1: public System::Windows::Forms::Form
{
private:
   MyMnemonicButton^ button1;

public private:
   System::Windows::Forms::ListBox^ ListBox1;

public:
   Form1()
      : Form()
   {
      
      // Set KeyPreview object to true to allow the form to process 
      // the key before the control with focus processes it.
      this->KeyPreview = true;
      
      // Add a MyMnemonicButton.  
      button1 = gcnew MyMnemonicButton;
      button1->Text = "&Click";
      button1->Location = System::Drawing::Point( 100, 120 );
      this->Controls->Add( button1 );
      
      // Initialize a ListBox control and the form itself.
      this->ListBox1 = gcnew System::Windows::Forms::ListBox;
      this->SuspendLayout();
      this->ListBox1->Location = System::Drawing::Point( 8, 8 );
      this->ListBox1->Name = "ListBox1";
      this->ListBox1->Size = System::Drawing::Size( 120, 95 );
      this->ListBox1->TabIndex = 0;
      this->ListBox1->Text = "Press a key";
      this->ClientSize = System::Drawing::Size( 292, 266 );
      this->Controls->Add( this->ListBox1 );
      this->Name = "Form1";
      this->Text = "Form1";
      this->ResumeLayout( false );
      
      // Associate the event-handling method with the
      // KeyDown event.
      this->KeyDown += gcnew KeyEventHandler( this, &Form1::Form1_KeyDown );
   }


private:

   // The form will handle all key events before the control with  
   // focus handles them.  Show the keys pressed by adding the
   // KeyCode object to ListBox1. Ensure the processing is passed
   // to the control with focus by setting the KeyEventArg.Handled
   // property to false.
   void Form1_KeyDown( Object^ /*sender*/, KeyEventArgs^ e )
   {
      ListBox1->Items->Add( e->KeyCode );
      e->Handled = false;
   }

};


[System::STAThreadAttribute]
int main()
{
   Application::Run( gcnew Form1 );
}

using System.Windows.Forms;
using System.Security.Permissions;

public class Form1:
    System.Windows.Forms.Form

    // Declare the controls contained on the form.
{
    private MyMnemonicButton button1;
    internal System.Windows.Forms.ListBox ListBox1;

    public Form1() : base()
    {        

        // Set KeyPreview object to true to allow the form to process 
        // the key before the control with focus processes it.
        this.KeyPreview = true;

        // Add a MyMnemonicButton.  
        button1 = new MyMnemonicButton();
        button1.Text = "&Click";
        button1.Location = new System.Drawing.Point(100, 120);
        this.Controls.Add(button1);

        // Initialize a ListBox control and the form itself.
        this.ListBox1 = new System.Windows.Forms.ListBox();
        this.SuspendLayout();
        this.ListBox1.Location = new System.Drawing.Point(8, 8);
        this.ListBox1.Name = "ListBox1";
        this.ListBox1.Size = new System.Drawing.Size(120, 95);
        this.ListBox1.TabIndex = 0;
        this.ListBox1.Text = "Press a key";
        this.ClientSize = new System.Drawing.Size(292, 266);
        this.Controls.Add(this.ListBox1);
        this.Name = "Form1";
        this.Text = "Form1";
        this.ResumeLayout(false);

        // Associate the event-handling method with the
        // KeyDown event.
        this.KeyDown += new KeyEventHandler(Form1_KeyDown);

    }

    // The form will handle all key events before the control with  
    // focus handles them.  Show the keys pressed by adding the
    // KeyCode object to ListBox1. Ensure the processing is passed
    // to the control with focus by setting the KeyEventArg.Handled
    // property to false.
    private void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        ListBox1.Items.Add(e.KeyCode);
        e.Handled = false;
    }

    [System.STAThreadAttribute]
    public static void Main()
    {
        Application.Run(new Form1());
    }

}


// This button is a simple extension of the button class that overrides
// the ProcessMnemonic method.  If the mnemonic is correctly entered,  
// the message box will appear and the click event will be raised.  
public class MyMnemonicButton:Button

    // This method makes sure the control is selectable and the 
    // mneumonic is correct before displaying the message box
    // and triggering the click event.
{
    [UIPermission(
        SecurityAction.Demand, Window = UIPermissionWindow.AllWindows)]
        protected override bool ProcessMnemonic(char inputChar)
    {

        if (CanSelect&&IsMnemonic(inputChar, this.Text))
        {
            MessageBox.Show("You've raised the click event " +
                "using the mnemonic.");
            this.PerformClick();
            return true;
        }
        return false;
    }

}
Imports System.Windows.Forms
Imports System.Security.Permissions

Public Class Form1
    Inherits System.Windows.Forms.Form

    ' Declare the controls contained on the form.
    Private WithEvents button1 As MyMnemonicButton
    Friend WithEvents ListBox1 As System.Windows.Forms.ListBox

    Public Sub New()
        MyBase.New()

        ' Set KeyPreview object to true to allow the form to process 
        ' the key before the control with focus processes it.
        Me.KeyPreview = True

        ' Add a MyMnemonicButton.  
        button1 = New MyMnemonicButton
        button1.Text = "&Click"
        button1.Location = New System.Drawing.Point(100, 120)
        Me.Controls.Add(button1)

        ' Initialize a ListBox control and the form itself.
        Me.ListBox1 = New System.Windows.Forms.ListBox
        Me.SuspendLayout()
        Me.ListBox1.Location = New System.Drawing.Point(8, 8)
        Me.ListBox1.Name = "ListBox1"
        Me.ListBox1.Size = New System.Drawing.Size(120, 95)
        Me.ListBox1.TabIndex = 0
        Me.ListBox1.Text = "Press a key"
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.ListBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

    ' The form will handle all key events before the control with  
    ' focus handles them.  Show the keys pressed by adding the
    ' KeyCode object to ListBox1. Ensure the processing is passed
    ' to the control with focus by setting the KeyEventArg.Handled
    ' property to false.
    Private Sub Form1_KeyDown(ByVal sender As Object, _
        ByVal e As KeyEventArgs) Handles MyBase.KeyDown
        ListBox1.Items.Add(e.KeyCode)
        e.Handled = False
    End Sub

    <System.STAThreadAttribute()> Public Shared Sub Main()
        Application.Run(New Form1)
    End Sub

End Class


' This button is a simple extension of the button class that overrides
' the ProcessMnemonic method.  If the mnemonic is correctly entered,  
' the message box will appear and the click event will be raised.  
Public Class MyMnemonicButton
    Inherits Button

    ' This method makes sure the control is selectable and the 
    ' mneumonic is correct before displaying the message box
    ' and triggering the click event.
    <System.Security.Permissions.UIPermission( _
    System.Security.Permissions.SecurityAction.Demand, Window:=UIPermissionWindow.AllWindows)> _
    Protected Overrides Function ProcessMnemonic( _
        ByVal inputChar As Char) As Boolean

        If (CanSelect And IsMnemonic(inputChar, Me.Text)) Then
            MessageBox.Show("You've raised the click event " _
                & "using the mnemonic.")
            Me.PerformClick()
            Return True
        End If
        Return False
    End Function

End Class

Комментарии

Если это свойство имеет значение true, форма получит все события KeyPress, KeyDown и KeyUp.When this property is set to true, the form will receive all KeyPress, KeyDown, and KeyUp events. После того как обработчики событий формы завершили обработку нажатия клавиши, нажатие клавиши будет назначено элементу управления с фокусом.After the form's event handlers have completed processing the keystroke, the keystroke is then assigned to the control with focus. Например, если свойство KeyPreview имеет значение true, а текущий выбранный элемент управления является TextBox, после того, как нажатие клавиши будет обработано обработчиками событий формы, элемент управления TextBox получит нажатую клавишу.For example, if the KeyPreview property is set to true and the currently selected control is a TextBox, after the keystroke is handled by the event handlers of the form the TextBox control will receive the key that was pressed. Чтобы обработчики событий клавиатуры обрабатывались только на уровне формы и не позволяли элементам управления принимать события клавиатуры, задайте для свойства KeyPressEventArgs.Handled в обработчике событий KeyPress формы значение true.To handle keyboard events only at the form level and not allow controls to receive keyboard events, set the KeyPressEventArgs.Handled property in your form's KeyPress event handler to true.

Это свойство можно использовать для обработки большинства нажатий клавиш в приложении и либо для обработки нажатия клавиши, либо для вызова соответствующего элемента управления для обработки нажатия клавиши.You can use this property to process most keystrokes in your application and either handle the keystroke or call the appropriate control to handle the keystroke. Например, если приложение использует ключи функций, может потребоваться обработать нажатия клавиш на уровне формы, а не писать код для каждого элемента управления, который может принимать события нажатия.For example, when an application uses function keys, you might want to process the keystrokes at the form level rather than writing code for each control that might receive keystroke events.

Примечание

Если форма не имеет видимых или включенных элементов управления, она автоматически получает все события клавиатуры.If a form has no visible or enabled controls, it automatically receives all keyboard events.

Примечание

Элемент управления в форме может быть запрограммирован на отмену принимаемых им нажатий клавиш.A control on a form may be programmed to cancel any keystrokes it receives. Поскольку элемент управления никогда не отправляет эти нажатия клавиш в форму, форма никогда не будет видеть их независимо от значения параметра KeyPreview.Since the control never sends these keystrokes to the form, the form will never see them regardless of the setting of KeyPreview.

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