Control.KeyDown Control.KeyDown Control.KeyDown Control.KeyDown Event

Definizione

Si verifica quando si preme un tasto mentre il controllo ha lo stato attivo.Occurs when a key is pressed while the control has focus.

public:
 event System::Windows::Forms::KeyEventHandler ^ KeyDown;
public event System.Windows.Forms.KeyEventHandler KeyDown;
member this.KeyDown : System.Windows.Forms.KeyEventHandler 
Public Custom Event KeyDown As KeyEventHandler 

Esempi

Il codice seguente viene illustrato come utilizzare il KeyDown evento per determinare il tipo di carattere inserito nel controllo.The following code example uses the KeyDown event to determine the type of character entered into the control.

   // Boolean flag used to determine when a character other than a number is entered.
private:
   bool nonNumberEntered;

   // Handle the KeyDown event to determine the type of character entered into the control.
   void textBox1_KeyDown( Object^ /*sender*/, System::Windows::Forms::KeyEventArgs^ e )
   {
      // Initialize the flag to false.
      nonNumberEntered = false;

      // Determine whether the keystroke is a number from the top of the keyboard.
      if ( e->KeyCode < Keys::D0 || e->KeyCode > Keys::D9 )
      {
         // Determine whether the keystroke is a number from the keypad.
         if ( e->KeyCode < Keys::NumPad0 || e->KeyCode > Keys::NumPad9 )
         {
            // Determine whether the keystroke is a backspace.
            if ( e->KeyCode != Keys::Back )
            {
               // A non-numerical keystroke was pressed.
               // Set the flag to true and evaluate in KeyPress event.
               nonNumberEntered = true;
            }
         }
      }
      //If shift key was pressed, it's not a number.
      if (Control::ModifierKeys == Keys::Shift) {
         nonNumberEntered = true;
      }
   }

   // This event occurs after the KeyDown event and can be used to prevent
   // characters from entering the control.
   void textBox1_KeyPress( Object^ /*sender*/, System::Windows::Forms::KeyPressEventArgs^ e )
   {
      // Check for the flag being set in the KeyDown event.
      if ( nonNumberEntered == true )
      {         // Stop the character from being entered into the control since it is non-numerical.
         e->Handled = true;
      }
   }
// Boolean flag used to determine when a character other than a number is entered.
private bool nonNumberEntered = false;

// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
    // Initialize the flag to false.
    nonNumberEntered = false;

    // Determine whether the keystroke is a number from the top of the keyboard.
    if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
    {
        // Determine whether the keystroke is a number from the keypad.
        if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
        {
            // Determine whether the keystroke is a backspace.
            if(e.KeyCode != Keys.Back)
            {
                // A non-numerical keystroke was pressed.
                // Set the flag to true and evaluate in KeyPress event.
                nonNumberEntered = true;
            }
        }
    }
    //If shift key was pressed, it's not a number.
    if (Control.ModifierKeys == Keys.Shift) {
        nonNumberEntered = true;
    }
}

// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
    // Check for the flag being set in the KeyDown event.
    if (nonNumberEntered == true)
    {
        // Stop the character from being entered into the control since it is non-numerical.
        e.Handled = true;
    }
}

' Boolean flag used to determine when a character other than a number is entered.
Private nonNumberEntered As Boolean = False


' Handle the KeyDown event to determine the type of character entered into the control.
Private Sub textBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
     Handles textBox1.KeyDown
    ' Initialize the flag to false.
    nonNumberEntered = False
  
    ' Determine whether the keystroke is a number from the top of the keyboard.
    If e.KeyCode < Keys.D0 OrElse e.KeyCode > Keys.D9 Then
        ' Determine whether the keystroke is a number from the keypad.
        If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
            ' Determine whether the keystroke is a backspace.
            If e.KeyCode <> Keys.Back Then
                ' A non-numerical keystroke was pressed. 
                ' Set the flag to true and evaluate in KeyPress event.
                nonNumberEntered = True
            End If
        End If
    End If
    'If shift key was pressed, it's not a number.
    If Control.ModifierKeys = Keys.Shift Then
        nonNumberEntered = true
    End If
End Sub 'textBox1_KeyDown


' This event occurs after the KeyDown event and can be used 
' to prevent characters from entering the control.
Private Sub textBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) _
    Handles textBox1.KeyPress
    ' Check for the flag being set in the KeyDown event.
    If nonNumberEntered = True Then
        ' Stop the character from being entered into the control since it is non-numerical.
        e.Handled = True
    End If
End Sub 'textBox1_KeyPress

Esempio di codice seguente viene illustrato l'ordine di generazione di KeyDown, KeyUp, KeyPress eventi e su come registrare i gestori di eventi su di essi.The following code example demonstrates the order of raising the KeyDown, KeyUp, KeyPress events, and how to register event handlers on them.

public partial class Form2 : Form
{
	public Form2()
	{
		InitializeComponent();
		textBox2.Multiline = true;
		textBox2.ScrollBars = ScrollBars.Both;

		//Setup events that listens on keypress
		textBox1.KeyDown += TextBox1_KeyDown;
		textBox1.KeyPress += TextBox1_KeyPress;
		textBox1.KeyUp += TextBox1_KeyUp;
	}

	// Handle the KeyUp event to print the type of character entered into the control.
	private void TextBox1_KeyUp(object sender, KeyEventArgs e)
	{
		textBox2.AppendText( $"KeyUp code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + "\r\n");
	}

	// Handle the KeyPress event to print the type of character entered into the control.
	private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
	{
		textBox2.AppendText( $"KeyPress keychar: {e.KeyChar}" + "\r\n");
	}

	// Handle the KeyDown event to print the type of character entered into the control.
	private void TextBox1_KeyDown(object sender, KeyEventArgs e)
	{
		textBox2.AppendText( $"KeyDown code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + "\r\n");
	}
}
Public Class Form2

    ' Handle the KeyDown event to print the type of character entered into the control.
    Private Sub TextBox1_KeyDown(sender As Object, e As KeyEventArgs) Handles TextBox1.KeyDown
        TextBox2.AppendText($"KeyDown code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + vbCrLf)
    End Sub

    ' Handle the KeyPress event to print the type of character entered into the control.
    Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
        TextBox2.AppendText($"KeyPress keychar: {e.KeyChar}" + vbCrLf)
    End Sub

    ' Handle the KeyUp event to print the type of character entered into the control.
    Private Sub TextBox1_KeyUp(sender As Object, e As KeyEventArgs) Handles TextBox1.KeyUp
        TextBox2.AppendText($"KeyUp code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + vbCrLf)
    End Sub

End Class

Commenti

Chiave eventi si verificano nell'ordine seguente:Key events occur in the following order:

  1. KeyDown

  2. KeyPress

  3. KeyUp

Per gestire gli eventi di tastiera solo a livello di form e non abilita altri controlli ricevere gli eventi della tastiera, impostare il KeyPressEventArgs.Handled proprietà del modulo KeyPress metodo di gestione degli eventi da true.To handle keyboard events only at the form level and not enable other controls to receive keyboard events, set the KeyPressEventArgs.Handled property in your form's KeyPress event-handling method to true. Determinate chiavi, ad esempio le chiavi, RETURN, ESC, freccia e TAB vengono gestiti automaticamente da tutti i controlli.Certain keys, such as the TAB, RETURN, ESC, and arrow keys are handled by controls automatically. Per impostare queste chiavi generi il KeyDown evento, è necessario eseguire l'override la IsInputKey metodo in ogni controllo nel form.To have these keys raise the KeyDown event, you must override the IsInputKey method in each control on your form. Il codice esegue l'override del IsInputKey sarà necessario determinare se viene premuto uno dei tasti speciali e restituiscono un valore di true.The code for the override of the IsInputKey would need to determine if one of the special keys is pressed and return a value of true. Invece di sostituire il IsInputKey metodo, è possibile gestire i PreviewKeyDown evento e impostare il IsInputKey proprietà true.Instead of overriding the IsInputKey method, you can handle the PreviewKeyDown event and set the IsInputKey property to true. Per un esempio di codice, vedere il PreviewKeyDown evento.For a code example, see the PreviewKeyDown event.

Per ulteriori informazioni sulla gestione degli eventi, consultare gestione e generazione di eventi.For more information about handling events, see Handling and Raising Events.

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