Control.KeyDown Gebeurtenis
Definitie
Belangrijk
Bepaalde informatie heeft betrekking op een voorlopige productversie die aanzienlijk kan worden gewijzigd voordat deze wordt uitgebracht. Microsoft biedt geen enkele expliciete of impliciete garanties met betrekking tot de informatie die hier wordt verstrekt.
Treedt op wanneer een toets wordt ingedrukt terwijl het besturingselement de focus heeft.
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 Gebeurtenistype
Voorbeelden
In het volgende codevoorbeeld wordt de KeyDown gebeurtenis gebruikt om het type teken te bepalen dat in het besturingselement is ingevoerd.
// 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)
{ // 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)
{
// 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
' 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
In het volgende codevoorbeeld ziet u de volgorde van het verhogen van , KeyDownKeyUpKeyPress gebeurtenissen en het registreren van gebeurtenis-handlers.
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
Opmerkingen
Belangrijke gebeurtenissen vinden plaats in de volgende volgorde:
Als u toetsenbordgebeurtenissen alleen op formulierniveau wilt afhandelen en andere besturingselementen niet wilt inschakelen voor het ontvangen van toetsenbordgebeurtenissen, stelt u de KeyPressEventArgs.Handled eigenschap in de methode voor gebeurtenisafhandeling van het formulier KeyPress in op true. Bepaalde toetsen, zoals tab, RETURN, ESC en pijltoetsen, worden automatisch verwerkt door besturingselementen. Als u deze sleutels de KeyDown gebeurtenis wilt laten genereren, moet u de IsInputKey methode in elk besturingselement in uw formulier overschrijven. De code voor de onderdrukking van de IsInputKey sleutel moet bepalen of een van de speciale toetsen wordt ingedrukt en een waarde van true. In plaats van de IsInputKey methode te overschrijven, kunt u de PreviewKeyDown gebeurtenis afhandelen en de IsInputKey eigenschap instellen op true. Zie de PreviewKeyDown gebeurtenis voor een codevoorbeeld.
Zie Gebeurtenissen verwerken en genereren voor meer informatie over het afhandelen van gebeurtenissen.