Vorgehensweise: Behandeln von Tastatureingaben auf Formularebene

Windows Forms bieten die Möglichkeit, Tastatureingaben auf Formularebene zu behandeln, bevor die Eingaben an ein Steuerelement weitergegeben werden. In diesem Thema wird gezeigt, wie Sie diese Aufgabe ausführen.

So behandeln Sie eine Tastatureingabe auf Formularebene

• Behandeln Sie das Ereignis KeyPress oder KeyDown im Startformular, und legen Sie die KeyPreview-Eigenschaft des Formulars auf true fest, damit Tastatureingaben vom Formular empfangen werden, bevor sie an irgendeines der Steuerelemente auf dem Formular weitergegeben werden. Im folgenden Codebeispiel wird das KeyPress-Ereignis behandelt, indem alle Zahlentasten erkannt und "1", "4" und "7" verarbeitet werden.

      // Detect all numeric characters at the form level and consume 1,
      // 4, and 7. Note that Form.KeyPreview must be set to true for this
      // event handler to be called.
  private:
      void Form1_KeyPress(Object^ sender, KeyPressEventArgs^ e)
      {
          if ((e->KeyChar >= '0') && (e->KeyChar <= '9'))
          {
              MessageBox::Show("Form.KeyPress: '" +
                  e->KeyChar.ToString() + "' pressed.");
  
              switch (e->KeyChar)
              {
              case '1':
              case '4':
              case '7':
                  MessageBox::Show("Form.KeyPress: '" +
                      e->KeyChar.ToString() + "' consumed.");
                  e->Handled = true;
                  break;
              }
          }
      }
  

  // Detect all numeric characters at the form level and consume 1,
  // 4, and 7. Note that Form.KeyPreview must be set to true for this
  // event handler to be called.
  void Form1_KeyPress(object sender, KeyPressEventArgs e)
  {
      if (e.KeyChar >= 48 && e.KeyChar <= 57)
      {
          MessageBox.Show("Form.KeyPress: '" +
              e.KeyChar.ToString() + "' pressed.");
  
          switch (e.KeyChar)
          {
              case (char)49:
              case (char)52:
              case (char)55:
                  MessageBox.Show("Form.KeyPress: '" +
                      e.KeyChar.ToString() + "' consumed.");
                  e.Handled = true;
                  break;
          }
      }
  }
  

  ' Detect all numeric characters at the form level and consume 1, 
  ' 4, and 7. Note that Form.KeyPreview must be set to true for this
  ' event handler to be called.
  Sub Form1_KeyPress(ByVal sender As Object, _
      ByVal e As KeyPressEventArgs) Handles Me.KeyPress
  
      If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
          MessageBox.Show(("Form.KeyPress: '" + _
              e.KeyChar.ToString() + "' pressed."))
  
          Select Case e.KeyChar
              Case ChrW(49), ChrW(52), ChrW(55)
                  MessageBox.Show(("Form.KeyPress: '" + _
                      e.KeyChar.ToString() + "' consumed."))
                  e.Handled = True
          End Select
      End If
  End Sub
  

Beispiel

Das folgende Codebeispiel ist die vollständige Anwendung für das vorstehende Codebeispiel. Die Anwendung enthält ein TextBox sowie mehrere andere Steuerelemente, die es Ihnen ermöglichen, den Fokus aus dem TextBox zu verschieben. Das KeyPress-Ereignis der Haupt-Form verarbeitet "1", "4" und "7", und das KeyPress-Ereignis des TextBox verarbeitet "2", "5" und "8", während die restlichen Tasten angezeigt werden. Vergleichen Sie die Ausgabe von MessageBox, wenn Sie eine Zahlentaste drücken, während das TextBox den Fokus besitzt, mit der Ausgabe von MessageBox, wenn sie eine Zahlentaste drücken, während eines der andere Steuerelemente den Fokus besitzt.

#using <System.Drawing.dll>
#using <System.Windows.Forms.dll>
#using <System.dll>

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Security::Permissions;

namespace KeyboardInputForm
{
    public ref class Form1 sealed: public Form, public IMessageFilter
    {
        // The following Windows message value is defined in Winuser.h.
    private:
        static const int WM_KEYDOWN = 0x100;
    private:
        TextBox^ inputTextBox;
    public:
        Form1()
        {
            inputTextBox = gcnew TextBox();
            this->AutoSize = true;
            Application::AddMessageFilter(this);
            FlowLayoutPanel^ panel = gcnew FlowLayoutPanel();
            panel->AutoSize = true;
            panel->FlowDirection = FlowDirection::TopDown;
            panel->Controls->Add(gcnew Button());
            panel->Controls->Add(gcnew RadioButton());
            panel->Controls->Add(inputTextBox);
            this->Controls->Add(panel);
            this->KeyPreview = true;
            this->KeyPress +=
                gcnew KeyPressEventHandler(this, &Form1::Form1_KeyPress);
            inputTextBox->KeyPress +=
                gcnew KeyPressEventHandler(this,
                &Form1::inputTextBox_KeyPress);
        }

        // Detect all numeric characters at the
        // application level and consume 0.
        virtual bool PreFilterMessage(Message% m)
        {
            // Detect key down messages.
            if (m.Msg == WM_KEYDOWN)
            {
                Keys keyCode =  (Keys)((int)m.WParam) & Keys::KeyCode;
                // Determine whether the keystroke is a number from the top of
                // the keyboard, or a number from the keypad.
                if (((keyCode >= Keys::D0) && (keyCode <= Keys::D9))
                    ||((keyCode >= Keys::NumPad0)
                    && (keyCode <= Keys::NumPad9)))
                {
                    MessageBox::Show(
                        "IMessageFilter.PreFilterMessage: '" +
                        keyCode.ToString() + "' pressed.");

                    if ((keyCode == Keys::D0) || (keyCode == Keys::NumPad0))
                    {
                        MessageBox::Show(
                            "IMessageFilter.PreFilterMessage: '" +
                            keyCode.ToString() + "' consumed.");
                        return true;
                    }
                }
            }

            // Forward all other messages.
            return false;
        }

        // Detect all numeric characters at the form level and consume 1,
        // 4, and 7. Note that Form.KeyPreview must be set to true for this
        // event handler to be called.
    private:
        void Form1_KeyPress(Object^ sender, KeyPressEventArgs^ e)
        {
            if ((e->KeyChar >= '0') && (e->KeyChar <= '9'))
            {
                MessageBox::Show("Form.KeyPress: '" +
                    e->KeyChar.ToString() + "' pressed.");

                switch (e->KeyChar)
                {
                case '1':
                case '4':
                case '7':
                    MessageBox::Show("Form.KeyPress: '" +
                        e->KeyChar.ToString() + "' consumed.");
                    e->Handled = true;
                    break;
                }
            }
        }

        // Detect all numeric characters at the TextBox level and consume
        // 2, 5, and 8.
    private:
        void inputTextBox_KeyPress(Object^ sender, KeyPressEventArgs^ e)
        {
            if ((e->KeyChar >= '0') && (e->KeyChar <= '9'))
            {
                MessageBox::Show("Control.KeyPress: '" +
                    e->KeyChar.ToString() + "' pressed.");

                switch (e->KeyChar)
                {
                case '2':
                case '5':
                case '8':
                    MessageBox::Show("Control.KeyPress: '" +
                        e->KeyChar.ToString() + "' consumed.");
                    e->Handled = true;
                    break;
                }
            }
        }
    };
}

[STAThread]
int main()
{
    Application::EnableVisualStyles();
    Application::Run(gcnew KeyboardInputForm::Form1());
}

using System;
using System.Drawing;
using System.Windows.Forms;

namespace KeyboardInputForm
{
    class Form1 : Form
    {
        TextBox TextBox1 = new TextBox();

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

        public Form1()
        {
            this.AutoSize = true;

            FlowLayoutPanel panel = new FlowLayoutPanel();
            panel.AutoSize = true;
            panel.FlowDirection = FlowDirection.TopDown;
            panel.Controls.Add(TextBox1);
            this.Controls.Add(panel);

            this.KeyPreview = true;
            this.KeyPress +=
                new KeyPressEventHandler(Form1_KeyPress);
            TextBox1.KeyPress +=
                new KeyPressEventHandler(TextBox1_KeyPress);
        }

        // Detect all numeric characters at the form level and consume 1,
        // 4, and 7. Note that Form.KeyPreview must be set to true for this
        // event handler to be called.
        void Form1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar >= 48 && e.KeyChar <= 57)
            {
                MessageBox.Show("Form.KeyPress: '" +
                    e.KeyChar.ToString() + "' pressed.");

                switch (e.KeyChar)
                {
                    case (char)49:
                    case (char)52:
                    case (char)55:
                        MessageBox.Show("Form.KeyPress: '" +
                            e.KeyChar.ToString() + "' consumed.");
                        e.Handled = true;
                        break;
                }
            }
        }

        // Detect all numeric characters at the TextBox level and consume
        // 2, 5, and 8.
        void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar >= 48 && e.KeyChar <= 57)
            {
                MessageBox.Show("Control.KeyPress: '" +
                    e.KeyChar.ToString() + "' pressed.");

                switch (e.KeyChar)
                {
                    case (char)50:
                    case (char)53:
                    case (char)56:
                        MessageBox.Show("Control.KeyPress: '" +
                            e.KeyChar.ToString() + "' consumed.");
                        e.Handled = true;
                        break;
                }
            }
        }
    }
}

Imports System.Drawing
Imports System.Windows.Forms

Namespace KeyboardInputForm

     Class Form1
      Inherits Form

        Private WithEvents TextBox1 As New TextBox()

      <STAThread()> _
      Public Shared Sub Main()
         Application.EnableVisualStyles()
         Application.Run(New Form1())
      End Sub

      Public Sub New()
         Me.AutoSize = True

         Dim panel As New FlowLayoutPanel()
         panel.AutoSize = True
         panel.FlowDirection = FlowDirection.TopDown
         panel.Controls.Add(TextBox1)
         Me.Controls.Add(panel)

         Me.KeyPreview = True
        End Sub

        ' Detect all numeric characters at the form level and consume 1, 
        ' 4, and 7. Note that Form.KeyPreview must be set to true for this
        ' event handler to be called.
        Sub Form1_KeyPress(ByVal sender As Object, _
            ByVal e As KeyPressEventArgs) Handles Me.KeyPress

            If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
                MessageBox.Show(("Form.KeyPress: '" + _
                    e.KeyChar.ToString() + "' pressed."))

                Select Case e.KeyChar
                    Case ChrW(49), ChrW(52), ChrW(55)
                        MessageBox.Show(("Form.KeyPress: '" + _
                            e.KeyChar.ToString() + "' consumed."))
                        e.Handled = True
                End Select
            End If
        End Sub

      ' Detect all numeric characters at the TextBox level and consume  
      ' 2, 5, and 8.
      Sub TextBox1_KeyPress(ByVal sender As Object, _
          ByVal e As KeyPressEventArgs) Handles TextBox1.KeyPress

         If e.KeyChar >= ChrW(48) And e.KeyChar <= ChrW(57) Then
            MessageBox.Show(("Control.KeyPress: '" + _
                e.KeyChar.ToString() + "' pressed."))

            Select Case e.KeyChar
               Case ChrW(50), ChrW(53), ChrW(56)
                  MessageBox.Show(("Control.KeyPress: '" + _
                      e.KeyChar.ToString() + "' consumed."))
                  e.Handled = True
            End Select
         End If
      End Sub

   End Class
End Namespace

Kompilieren des Codes

Für dieses Beispiel benötigen Sie Folgendes:

• Verweise auf die Assemblys "System", "System.Drawing" und "System.Windows.Forms".

Siehe auch

• Tastatureingaben in einer Windows Forms-Anwendung