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

定義

發生於按下按鍵且焦點在控制項時。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 

範例

下列程式碼範例使用KeyDown事件,以判斷輸入控制項的字元類型。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

下列程式碼範例示範的引發順序KeyDownKeyUpKeyPress事件,以及如何註冊其上的事件處理常式。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

備註

索引鍵的事件發生順序如下:Key events occur in the following order:

  1. KeyDown

  2. KeyPress

  3. KeyUp

若要處理只能在表單層級的鍵盤事件,並啟用以接收鍵盤事件的其他控制項,將KeyPressEventArgs.Handled在您的表單中的屬性KeyPress事件處理方法trueTo 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. 特定金鑰,例如 tab 鍵,傳回時,esc 鍵,和箭號會自動處理控制項。Certain keys, such as the TAB, RETURN, ESC, and arrow keys are handled by controls automatically. 若要有這些索引鍵,會引發KeyDown您必須覆寫事件,IsInputKey您的表單上的每個控制項中的方法。To have these keys raise the KeyDown event, you must override the IsInputKey method in each control on your form. 覆寫的程式碼IsInputKey想要判斷其中一個特殊按鍵已按下,並傳回值trueThe 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. 而不是覆寫IsInputKey方法中,您可以處理PreviewKeyDown事件以及組IsInputKey屬性設trueInstead of overriding the IsInputKey method, you can handle the PreviewKeyDown event and set the IsInputKey property to true. 如需程式碼範例,請參閱PreviewKeyDown事件。For a code example, see the PreviewKeyDown event.

如需有關如何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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