Form.KeyPreview Vlastnost

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

Hodnota vlastnosti

true pokud formulář obdrží všechny klíčové události; false pokud aktuálně vybraný ovládací prvek ve formuláři přijímá klíčové události. Výchozí formát je false.

Příklady

Následující příklad ukazuje nastavení vlastnosti formuláře KeyPreview na true a zpracování událostí klíče na úrovni formuláře. Pokud chcete spustit příklad, vložte do prázdného formuláře následující kód.

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;

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.
    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

Poznámky

Pokud je tato vlastnost nastavená na true, formulář obdrží všechny KeyPressudálosti , KeyDowna KeyUp . Jakmile obslužné rutiny událostí formuláře dokončí zpracování stisknutí klávesy, je stisknutí klávesy přiřazeno ovládacímu prvku s fokusem. Pokud je například KeyPreview vlastnost nastavena na true hodnotu a aktuálně vybraným ovládacím prvkem TextBoxje , po stisknutí klávesy obslužnými rutiny události formuláře TextBox obdrží ovládací prvek stisknutou klávesu. Pokud chcete zpracovávat události klávesnice pouze na úrovni formuláře a nechcete ovládacím prvkům povolit příjem událostí klávesnice, nastavte KeyPressEventArgs.Handled vlastnost v obslužné rutině KeyPress události formuláře na truehodnotu .

Tuto vlastnost můžete použít ke zpracování většiny klávesových úhozů v aplikaci a zpracování stisknutí kláves nebo volání příslušného ovládacího prvku pro zpracování stisknutí kláves. Pokud například aplikace používá funkční klávesy, můžete chtít zpracovávat stisknutí kláves na úrovni formuláře a nepsat kód pro každý ovládací prvek, který může přijímat události stisknutí klávesy.

Platí pro

Viz také

• KeyPress
• KeyDown
• KeyUp