如何：修改标准控件中的键盘输入

更新：2007 年 11 月

Windows 窗体提供了使用和修改键盘输入的功能。使用键是指在方法或事件处理程序中对键进行处理，以便消息队列中随后的其他方法和事件不会收到键值。修改键是指修改键值，以便消息队列中随后的方法和事件处理程序收到另一个键值。本主题显示如何完成这些任务。

使用键

• 在 KeyPress 事件处理程序中，将 KeyPressEventArgs 类的 Handled 属性设置为 true。

  - 或 -

  在 KeyDown 事件处理程序中，将 KeyEventArgs 类的 Handled 属性设置为 true。

  说明：
  如果在 KeyDown 事件处理程序中设置 Handled 属性，将不会阻止对当前按键引发 KeyPress 和 KeyUp 事件。请将 SuppressKeyPress 属性用于此目的。

  下面的示例摘录自 switch 语句，该语句检查 KeyPress 事件处理程序所收到的 KeyPressEventArgs 的 KeyChar 属性。此代码使用“A”和“a”字符键。

  ' Consume 'A' and 'a'.
  Case ChrW(65), ChrW(97)
      MessageBox.Show(("Control.KeyPress: '" + _
          e.KeyChar.ToString() + "' consumed."))
      e.Handled = True
  

  // Consume 'A' and 'a'.
  case (char)65:
  case (char)97:
      MessageBox.Show("Control.KeyPress: '" +
          e.KeyChar.ToString() + "' consumed.");
      e.Handled = true;
      break;
  

修改标准字符键

• 在 KeyPress 事件处理程序中，将 KeyPressEventArgs 类的 KeyChar 属性设置为新字符键的值。

  下面的示例摘录自 switch 语句，该语句将“B”修改为“A”，并将“b”修改为“a”。注意，KeyPressEventArgs 的 Handled 属性设置为 false，以便将新的键值传播到消息队列中的其他方法和事件。

      ' Modify 'B' to 'A' and forward the key.
  Case ChrW(66)
      MessageBox.Show(("Control.KeyPress: '" + _
          e.KeyChar.ToString() + "' replaced by 'A'."))
      e.KeyChar = ChrW(65)
      e.Handled = False
  
      ' Modify 'b' to 'a' and forward the key.
  Case ChrW(98)
      MessageBox.Show(("Control.KeyPress: '" + _
          e.KeyChar.ToString() + "' replaced by 'a'."))
      e.KeyChar = ChrW(97)
      e.Handled = False
  

  // Detect 'B', modify it to 'A', and forward the key.
  case (char)66:
      MessageBox.Show("Control.KeyPress: '" +
          e.KeyChar.ToString() + "' replaced by 'A'.");
      e.KeyChar = (char)65;
      e.Handled = false;
      break;
  
  // Detect 'b', modify it to 'a', and forward the key.
  case (char)98:
      MessageBox.Show("Control.KeyPress: '" +
          e.KeyChar.ToString() + "' replaced by 'a'.");
      e.KeyChar = (char)97;
      e.Handled = false;
      break;
  

修改非字符键

• 重写用于处理 Windows 消息的 Control 方法，并检测 WM_KEYDOWN 或 WM_SYSKEYDOWN 消息，然后将 Message 参数的 WParam 属性设置为表示新的非字符键的 Keys 值。

  下面的代码示例演示如何重写控件的 PreProcessMessage 方法，以检测键 F1 到 F9，并将任何 F3 键修改为按 F1 键。有关可以重写以截获键盘消息的 Control 方法的更多信息，请参见 Windows 窗体应用程序中的用户输入 和 键盘输入工作原理。

  ' Detect F1 through F9 during preprocessing and modify F3.
  Public Overrides Function PreProcessMessage(ByRef m As Message) _
      As Boolean
  
      If m.Msg = WM_KEYDOWN Then
          Dim keyCode As Keys = CType(m.WParam, Keys) And Keys.KeyCode
  
          ' Detect F1 through F9.
          Select Case keyCode
              Case Keys.F1, Keys.F2, Keys.F3, Keys.F4, Keys.F5, _
                   Keys.F6, Keys.F7, Keys.F8, Keys.F9
  
                  MessageBox.Show(("Control.PreProcessMessage: '" + _
                      keyCode.ToString() + "' pressed."))
  
                  ' Replace F3 with F1, so that ProcessKeyMessage will  
                  ' receive F1 instead of F3.
                  If keyCode = Keys.F3 Then
                      m.WParam = CType(Keys.F1, IntPtr)
                      MessageBox.Show(("Control.PreProcessMessage: '" + _
                          keyCode.ToString() + "' replaced by F1."))
                  End If
          End Select
      End If
  
      ' Send all other messages to the base method.
      Return MyBase.PreProcessMessage(m)
  End Function
  

  // Detect F1 through F9 during preprocessing and modify F3.
  public override bool PreProcessMessage(ref Message m)
  {
      if (m.Msg == WM_KEYDOWN)
      {
          Keys keyCode = (Keys)m.WParam & Keys.KeyCode;
  
          // Detect F1 through F9.
          switch (keyCode)
          {
              case Keys.F1:
              case Keys.F2:
              case Keys.F3:
              case Keys.F4:
              case Keys.F5:
              case Keys.F6:
              case Keys.F7:
              case Keys.F8:
              case Keys.F9:
  
                  MessageBox.Show("Control.PreProcessMessage: '" +
                    keyCode.ToString() + "' pressed.");
  
                  // Replace F3 with F1, so that ProcessKeyMessage will  
                  // receive F1 instead of F3.
                  if (keyCode == Keys.F3)
                  {
                      m.WParam = (IntPtr)Keys.F1;
                      MessageBox.Show("Control.PreProcessMessage: '" +
                          keyCode.ToString() + "' replaced by F1.");
                  }
                  break;
          }
      }
  
      // Send all other messages to the base method.
      return base.PreProcessMessage(ref m);
  }
  

示例

下面的代码示例是上述各节中的全部代码示例应用程序。应用程序使用从 TextBox 类派生的自定义控件来使用和修改键盘输入。

Imports System
Imports System.Drawing
Imports System.Security
Imports System.Security.Permissions
Imports System.Windows.Forms


Namespace KeyboardInput
<System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _ 
    Class Form1
        Inherits Form

        ' The following Windows message value is defined in Winuser.h.
        Private WM_KEYDOWN As Integer = &H100
        Private WithEvents CustomTextBox1 As New CustomTextBox()

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

        Public Sub New()
            Me.AutoSize = True
            Me.Controls.Add(CustomTextBox1)
        End Sub

        ' Consume and modify several character keys.
        Sub CustomTextBox1_KeyPress(ByVal sender As Object, _
            ByVal e As KeyPressEventArgs) Handles CustomTextBox1.KeyPress

            Select Case e.KeyChar

                ' Consume 'A' and 'a'.
                Case ChrW(65), ChrW(97)
                    MessageBox.Show(("Control.KeyPress: '" + _
                        e.KeyChar.ToString() + "' consumed."))
                    e.Handled = True

                    ' Modify 'B' to 'A' and forward the key.
                Case ChrW(66)
                    MessageBox.Show(("Control.KeyPress: '" + _
                        e.KeyChar.ToString() + "' replaced by 'A'."))
                    e.KeyChar = ChrW(65)
                    e.Handled = False

                    ' Modify 'b' to 'a' and forward the key.
                Case ChrW(98)
                    MessageBox.Show(("Control.KeyPress: '" + _
                        e.KeyChar.ToString() + "' replaced by 'a'."))
                    e.KeyChar = ChrW(97)
                    e.Handled = False
            End Select
        End Sub
    End Class

<System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _ 
    Public Class CustomTextBox
        Inherits TextBox

        ' The following Windows message value is defined in Winuser.h.
        Private WM_KEYDOWN As Integer = &H100

        Public Sub New()
            Me.Size = New Size(100, 100)
            Me.AutoSize = False
        End Sub

        ' Detect F1 through F9 during preprocessing and modify F3.
        Public Overrides Function PreProcessMessage(ByRef m As Message) _
            As Boolean

            If m.Msg = WM_KEYDOWN Then
                Dim keyCode As Keys = CType(m.WParam, Keys) And Keys.KeyCode

                ' Detect F1 through F9.
                Select Case keyCode
                    Case Keys.F1, Keys.F2, Keys.F3, Keys.F4, Keys.F5, _
                         Keys.F6, Keys.F7, Keys.F8, Keys.F9

                        MessageBox.Show(("Control.PreProcessMessage: '" + _
                            keyCode.ToString() + "' pressed."))

                        ' Replace F3 with F1, so that ProcessKeyMessage will  
                        ' receive F1 instead of F3.
                        If keyCode = Keys.F3 Then
                            m.WParam = CType(Keys.F1, IntPtr)
                            MessageBox.Show(("Control.PreProcessMessage: '" + _
                                keyCode.ToString() + "' replaced by F1."))
                        End If
                End Select
            End If

            ' Send all other messages to the base method.
            Return MyBase.PreProcessMessage(m)
        End Function

        ' Detect F1 through F9 during processing.
        Protected Overrides Function ProcessKeyMessage(ByRef m As Message) _
            As Boolean

            If m.Msg = WM_KEYDOWN Then
                Dim keyCode As Keys = CType(m.WParam, Keys) And Keys.KeyCode

                ' Detect F1 through F9.
                Select Case keyCode
                    Case Keys.F1, Keys.F2, Keys.F3, Keys.F4, Keys.F5, _
                         Keys.F6, Keys.F7, Keys.F8, Keys.F9

                        MessageBox.Show(("Control.ProcessKeyMessage: '" + _
                            keyCode.ToString() + "' pressed."))
                End Select
            End If

            ' Send all messages to the base method.
            Return MyBase.ProcessKeyMessage(m)
        End Function

    End Class
End Namespace

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

namespace KeyboardInput
{
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
    class Form1 : Form
    {
        // The following Windows message value is defined in Winuser.h.
        private int WM_KEYDOWN = 0x100;
        CustomTextBox CustomTextBox1 = new CustomTextBox();

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

        public Form1()
        {
            this.AutoSize = true;
            this.Controls.Add(CustomTextBox1);
            CustomTextBox1.KeyPress +=
                new KeyPressEventHandler(CustomTextBox1_KeyPress);
        }

        // Consume and modify several character keys.
        void CustomTextBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            switch (e.KeyChar)
            {
                // Consume 'A' and 'a'.
                case (char)65:
                case (char)97:
                    MessageBox.Show("Control.KeyPress: '" +
                        e.KeyChar.ToString() + "' consumed.");
                    e.Handled = true;
                    break;

                // Detect 'B', modify it to 'A', and forward the key.
                case (char)66:
                    MessageBox.Show("Control.KeyPress: '" +
                        e.KeyChar.ToString() + "' replaced by 'A'.");
                    e.KeyChar = (char)65;
                    e.Handled = false;
                    break;

                // Detect 'b', modify it to 'a', and forward the key.
                case (char)98:
                    MessageBox.Show("Control.KeyPress: '" +
                        e.KeyChar.ToString() + "' replaced by 'a'.");
                    e.KeyChar = (char)97;
                    e.Handled = false;
                    break;
            }
        }
    }
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
    public class CustomTextBox : TextBox
    {
        // The following Windows message value is defined in Winuser.h.
        private int WM_KEYDOWN = 0x100;

        public CustomTextBox()
        {
            this.Size = new Size(100, 100);
            this.AutoSize = false;
        }

        // Detect F1 through F9 during preprocessing and modify F3.
        public override bool PreProcessMessage(ref Message m)
        {
            if (m.Msg == WM_KEYDOWN)
            {
                Keys keyCode = (Keys)m.WParam & Keys.KeyCode;

                // Detect F1 through F9.
                switch (keyCode)
                {
                    case Keys.F1:
                    case Keys.F2:
                    case Keys.F3:
                    case Keys.F4:
                    case Keys.F5:
                    case Keys.F6:
                    case Keys.F7:
                    case Keys.F8:
                    case Keys.F9:

                        MessageBox.Show("Control.PreProcessMessage: '" +
                          keyCode.ToString() + "' pressed.");

                        // Replace F3 with F1, so that ProcessKeyMessage will  
                        // receive F1 instead of F3.
                        if (keyCode == Keys.F3)
                        {
                            m.WParam = (IntPtr)Keys.F1;
                            MessageBox.Show("Control.PreProcessMessage: '" +
                                keyCode.ToString() + "' replaced by F1.");
                        }
                        break;
                }
            }

            // Send all other messages to the base method.
            return base.PreProcessMessage(ref m);
        }

        // Detect F1 through F9 during processing.
        protected override bool ProcessKeyMessage(ref Message m)
        {
            if (m.Msg == WM_KEYDOWN)
            {
                Keys keyCode = (Keys)m.WParam & Keys.KeyCode;

                // Detect F1 through F9.
                switch (keyCode)
                {
                    case Keys.F1:
                    case Keys.F2:
                    case Keys.F3:
                    case Keys.F4:
                    case Keys.F5:
                    case Keys.F6:
                    case Keys.F7:
                    case Keys.F8:
                    case Keys.F9:

                        MessageBox.Show("Control.ProcessKeyMessage: '" +
                          keyCode.ToString() + "' pressed.");
                        break;
                }
            }

            // Send all messages to the base method.
            return base.ProcessKeyMessage(ref m);
        }
    }
}

编译代码

此示例要求：

• 对 System、System.Drawing 和 System.Windows.Forms 程序集的引用。

有关从 Visual Basic 或 Visual C# 的命令行生成此示例的信息，请参见从命令行生成 (Visual Basic) 或在命令行上使用 csc.exe 生成。也可以通过将代码粘贴到新项目，在 Visual Studio 中生成此示例。 有关更多信息，请参见如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例 和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例 和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例 和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例 和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例.

请参见

概念

Windows 窗体应用程序中的用户输入

键盘输入工作原理

其他资源

Windows 窗体应用程序中的键盘输入