Windows 窗体—— 键盘输入工作原理

方法	注释
PreFilterMessage	此方法在应用程序级截获排队的（也称为已发送的）Windows 消息。
PreProcessMessage	此方法在 Windows 消息处理前在窗体和控件级截获它们。
WndProc	此方法在窗体和控件级处理 Windows 消息。
DefWndProc	此方法在窗体和控件级执行 Windows 消息的默认处理。 这提供了窗口的最小功能。
OnNotifyMessage	此方法在消息处理后在窗体和控件级截获它们。 若要调用此方法，必须设置 EnableNotifyMessage 样式位。

KeyDown 事件的预处理相关方法:ProcessCmdKey、IsInputKey、ProcessDialogKey

KeyPress 事件的预处理相关方法:IsInputChar、ProcessDialogChar

Control的ProcessCmdKey方法：该方法处理命令键，命令键的优先级高于常规键。命令键的例子包括快捷键和菜单快捷方式

// true:将不调度键消息，而且将不发生键事件
// false:将调用IsInputKey
[SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode), SecurityPermission(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
protected virtual bool ProcessCmdKey(ref Message msg, Keys keyData)
{
    ContextMenu menu = (ContextMenu) this.Properties.GetObject(PropContextMenu);
    return (((menu != null) && menu.ProcessCmdKey(ref msg, keyData, this)) || ((this.parent != null) && this.parent.ProcessCmdKey(ref msg, keyData)));
}

Control的IsInputKey方法：

// true:表示该控件为常规字符，将引发 KeyDown 事件
// false:表示还没有做处理，将会调用ProcessDialogKey进行处理

[UIPermission(SecurityAction.InheritanceDemand, Window=UIPermissionWindow.AllWindows)]
protected virtual bool IsInputKey(Keys keyData)
{
    // 1.检查该键是否为需要预处理的特殊键
    // Alt需要特殊处理
    if ((keyData & Keys.Alt) == Keys.Alt)
    {
        return false;
    }
    int num = ;
    switch ((keyData & Keys.KeyCode))
    {
        case Keys.Left:
        case Keys.Up:
        case Keys.Right:
        case Keys.Down:
            num = ;
            break;

        case Keys.Tab:
            num = ;
            break;
    }
    // 2.检查它是否为应引发KeyDown 事件并且被调度到某个控件的普通字符键
    // IsHandleCreated 指示控件是否有与它关联的句柄 
    return (this.IsHandleCreated && ((((int) ((long) this.SendMessage(0x87, , ))) & num) != )); 
}

　　※预处理的键包括 Tab、Return、ESC 以及向上键、向下键、向左键和向右键。

ProcessDialogKey:此方法在控件内实现特殊功能（如在控件及其父级之间切换焦点）的物理按键。 如果中间控件不处理该键，则将调用父控件的 ProcessDialogKey，直至层次结构中的最顶端控件。

// true:将完成预处理，而且将不生成按键事件。
// false:将发生 KeyDown 事件
[UIPermission(SecurityAction.InheritanceDemand, Window=UIPermissionWindow.AllWindows), UIPermission(SecurityAction.LinkDemand, Window=UIPermissionWindow.AllWindows)]
protected virtual bool ProcessDialogKey(Keys keyData)
{
    return ((this.parent != null) && this.parent.ProcessDialogKey(keyData));
}

处理键盘消息

ProcessKeyMessage：此方法处理由控件的 WndProc 方法接收的所有键盘消息。

[SecurityPermission(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode), SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
protected internal virtual bool ProcessKeyMessage(ref Message m)
{
    return (((this.parent != null) && this.parent.ProcessKeyPreview(ref m)) || this.ProcessKeyEventArgs(ref m));
}

ProcessKeyPreview：此方法将键盘消息发送到控件的父控件。 如果 ProcessKeyPreview 返回 true，则将不生成键事件；否则将调用 ProcessKeyEventArgs。

[SecurityPermission(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode), SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
protected virtual bool ProcessKeyPreview(ref Message m)
{
    return ((this.parent != null) && this.parent.ProcessKeyPreview(ref m));
}

ProcessKeyEventArgs：此方法根据需要引发 KeyDown、KeyPress 和 KeyUp 事件。

[SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode), SecurityPermission(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
protected virtual bool ProcessKeyEventArgs(ref Message m)
{
    KeyEventArgs e = null;
    KeyPressEventArgs args2 = null;
    IntPtr zero = IntPtr.Zero;
    if ((m.Msg == 0x102) || (m.Msg == 0x106))
    {
        int imeWmCharsToIgnore = this.ImeWmCharsToIgnore;
        if (imeWmCharsToIgnore > )
        {
            imeWmCharsToIgnore--;
            this.ImeWmCharsToIgnore = imeWmCharsToIgnore;
            return false;
        }
        args2 = new KeyPressEventArgs((char) ((ushort) ((long) m.WParam)));
        // OnKeyPress
        this.OnKeyPress(args2);
        zero = (IntPtr) args2.KeyChar;
    }
    else if (m.Msg == 0x286)
    {
        int num2 = this.ImeWmCharsToIgnore;
        if (Marshal.SystemDefaultCharSize == )
        {
            char ch = '\0';
            byte[] lpMultiByteStr = new byte[] { (byte) (((int) ((long) m.WParam)) >> ), (byte) ((long) m.WParam) };
            char[] lpWideCharStr = new char[];
            int num3 = UnsafeNativeMethods.MultiByteToWideChar(, , lpMultiByteStr, lpMultiByteStr.Length, lpWideCharStr, );
            if (num3 <= )
            {
                throw new Win32Exception();
            }
            lpWideCharStr = new char[num3];
            UnsafeNativeMethods.MultiByteToWideChar(, , lpMultiByteStr, lpMultiByteStr.Length, lpWideCharStr, lpWideCharStr.Length);
            if (lpWideCharStr[] != '\0')
            {
                ch = lpWideCharStr[];
                num2 += ;
            }
            else if ((lpWideCharStr[] == '\0') && (lpWideCharStr.Length >= ))
            {
                ch = lpWideCharStr[];
                num2++;
            }
            this.ImeWmCharsToIgnore = num2;
            args2 = new KeyPressEventArgs(ch);
        }
        else
        {
            num2 +=  - Marshal.SystemDefaultCharSize;
            this.ImeWmCharsToIgnore = num2;
            args2 = new KeyPressEventArgs((char) ((ushort) ((long) m.WParam)));
        }
        char keyChar = args2.KeyChar;
        // OnKeyPress
        this.OnKeyPress(args2);
        if (args2.KeyChar == keyChar)
        {
            zero = m.WParam;
        }
        else if (Marshal.SystemDefaultCharSize == )
        {
            string wideStr = new string(new char[] { args2.KeyChar });
            byte[] pOutBytes = null;
            int num4 = UnsafeNativeMethods.WideCharToMultiByte(, , wideStr, wideStr.Length, null, , IntPtr.Zero, IntPtr.Zero);
            if (num4 >= )
            {
                pOutBytes = new byte[num4];
                UnsafeNativeMethods.WideCharToMultiByte(, , wideStr, wideStr.Length, pOutBytes, pOutBytes.Length, IntPtr.Zero, IntPtr.Zero);
                int num5 = Marshal.SizeOf(typeof(IntPtr));
                if (num4 > num5)
                {
                    num4 = num5;
                }
                long num6 = ;
                for (int i = ; i < num4; i++)
                {
                    num6 = num6 << ;
                    num6 |= pOutBytes[i];
                }
                zero = (IntPtr) num6;
            }
            else if (num4 == )
            {
                pOutBytes = new byte[num4];
                UnsafeNativeMethods.WideCharToMultiByte(, , wideStr, wideStr.Length, pOutBytes, pOutBytes.Length, IntPtr.Zero, IntPtr.Zero);
                zero = (IntPtr) pOutBytes[];
            }
            else
            {
                zero = m.WParam;
            }
        }
        else
        {
            zero = (IntPtr) args2.KeyChar;
        }
    }
    else
    {
        e = new KeyEventArgs(((Keys) ((int) ((long) m.WParam))) | ModifierKeys);
        if ((m.Msg == 0x100) || (m.Msg == ))
        {
            // OnKeyDown
            this.OnKeyDown(e);
        }
        else
        {
            // OnKeyUp
            this.OnKeyUp(e);
        }
    }
    if (args2 != null)
    {
        m.WParam = zero;
        return args2.Handled;
    }
    if (e.SuppressKeyPress)
    {
        this.RemovePendingMessages(0x102, 0x102);
        this.RemovePendingMessages(0x106, 0x106);
        this.RemovePendingMessages(0x286, 0x286);
    }
    return e.Handled;
}

来源：键盘输入工作原理