Como: Lidar com entrada de teclado no nível do formulário

Os Formulários do Windows fornecem a capacidade de tratar mensagens de teclado no nível do formulário, antes que as mensagens alcancem um controle.Este tópico mostra como realizar estas tarefas.

Para manipular uma mensagem de teclado no nível do formulário

• Trate o evento do formulário de inicialização KeyPress ou KeyDown e defina a propriedade KeyPreview do formulário para true de modo que as mensagens do teclado sejam recebidas pelo formulário antes que elas atinjam os controles do formulário.O seguinte código exemplo manipula o evento KeyPress, detectando todas as teclas de numéricas e consumindo '1', '4' e '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.
  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 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.
  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;
              }
          }
      }
  

Exemplo

O código exemplo a seguir é o aplicativo inteiro para o exemplo acima.O aplicativo inclui um TextBox juntamente com vários outros controles que permitem que você mova o foco do TextBox.O evento KeyPress do principal Form consome '1', '4' e '7', e o evento KeyPress de TextBox consome '2', '5' e '8' e exibe as teclas restantes.Compare a saída MessageBox quando você pressiona uma tecla de número enquanto o TextBox tem foco com a saída MessageBox quando você pressiona uma tecla de número enquanto o foco estiver em um dos outros controles.

Imports System
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

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;
                }
            }
        }
    }
}

#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.
        [SecurityPermission(SecurityAction::LinkDemand,
            Flags=SecurityPermissionFlag::UnmanagedCode)]
        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());
}

Compilando o código

Este exemplo requer:

• Referências para as montagens (assemblys) do System, System.Drawing e System.Windows.Forms.

Para obter informações sobre como criar este exemplo a partir da linha de comando para Visual Basic ou Visual C#, consulte Criando a partir da linha de comando (Visual Basic) ou Linha de comando criando com csc.exe.Você também pode construir este exemplo no Visual Studio colando o código em um novo projeto.

Consulte também

Outros recursos

A Entrada do Teclado em um aplicativo de Formulários do Windows