Procedimiento para controlar la entrada de teclado en el formulario

  • Artículo

Windows Forms permite controlar los mensajes del teclado en el nivel de formulario, antes de que los mensajes lleguen a un control. En este tema se muestra cómo realizar esta tarea.

Para controlar un mensaje de teclado en el nivel de formulario

  • Controle los eventos KeyPress o KeyDown del formulario de inicio y establezca la propiedad KeyPreview del formulario en true para que el formulario reciba los mensajes del teclado antes de que lleguen a los controles del formulario. Para controlar el evento KeyPress, el siguiente código de ejemplo detecta todas las teclas numéricas y consume las teclas '1', '4' y '7'.

        // 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

Ejemplo

El siguiente ejemplo de código es toda la aplicación del ejemplo anterior. La aplicación incluye un TextBox además de otros controles que permiten mover el foco desde el TextBox. El evento KeyPress del Form principal consume '1', '4' y '7' y el evento KeyPress del TextBox consume '2', '5' y '8' mientras muestra las teclas restantes. Compare el resultado de MessageBox cuando se presiona una tecla de número mientras el TextBox tiene el foco con el resultado de MessageBox cuando se presiona una tecla numérica mientras el foco está en otro de los controles.

#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

Compilar el código

Para este ejemplo se necesita:

  • Referencias a los ensamblados System, System.Drawing y System.Windows.Forms.

Vea también