c# - 拖放时可以使用鼠标滚轮吗？

Question

在 WinForms 中，在调用 DoDragDrop 开始拖动项目后，控件不再使用鼠标滚轮滚动，并且控件的 MouseWheel 事件不再被调用，直到用户放下他拖动的任何东西。

有没有办法让鼠标滚轮在拖动时起作用？

Answer 1

您可以获得带有键盘 Hook 的全局 MouseWheel。

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using Microsoft.Win32.SafeHandles;

using BOOL = System.Boolean;
using DWORD = System.UInt32;
using HHOOK = SafeHookHandle;
using HINSTANCE = System.IntPtr;
using HOOKPROC = HookProc;
using LPARAM = System.IntPtr;
using LRESULT = System.IntPtr;
using POINT = System.Drawing.Point;
using ULONG_PTR = System.IntPtr;
using WPARAM = System.IntPtr;

public delegate LRESULT HookProc(int nCode, WPARAM wParam, LPARAM lParam);

internal static class NativeMethods
{
    [DllImport("User32.dll", SetLastError = true)]
    internal static extern HHOOK SetWindowsHookEx(
        HookType idHook,
        HOOKPROC lpfn,
        HINSTANCE hMod,
        DWORD dwThreadId);

    [DllImport("User32.dll")]
    internal static extern LRESULT CallNextHookEx(
        HHOOK hhk,
        int nCode,
        WPARAM wParam,
        LPARAM lParam);

    [DllImport("User32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    internal static extern BOOL UnhookWindowsHookEx(
        IntPtr hhk);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr GetModuleHandle(string lpModuleName);
}

internal static class NativeTypes
{
    internal enum MSLLHOOKSTRUCTFlags : uint
    {
        LLMHF_INJECTED = 0x00000001U,
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct MSLLHOOKSTRUCT
    {
        internal POINT pt;
        internal DWORD mouseData;
        internal MSLLHOOKSTRUCTFlags flags;
        internal DWORD time;
        internal ULONG_PTR dwExtraInfo;
    }
}

internal static class NativeConstants
{
    internal const int WH_MOUSE_LL = 14;

    internal const int HC_ACTION = 0;

    internal const int WM_MOUSEWHEEL = 0x020A;
    internal const int WM_MOUSEHWHEEL = 0x020E;

    internal const int WHEEL_DELTA = 120;
}

public enum HookType
{
    LowLevelMouseHook = NativeConstants.WH_MOUSE_LL
}

public enum HookScope
{
    LowLevelGlobal,
}

public class SafeHookHandle : SafeHandleZeroOrMinusOneIsInvalid
{
    private SafeHookHandle() : base(true) { }

    public static SafeHookHandle SetWindowsHook(HookType idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId)
    {
        var hhk = NativeMethods.SetWindowsHookEx(idHook, lpfn, hMod, dwThreadId);

        if(hhk.IsInvalid)
        {
            throw new Win32Exception();
        }
        else
        {
            return hhk;
        }
    }

    public IntPtr CallNextHook(int nCode, IntPtr wParam, IntPtr lParam)
    {
        return NativeMethods.CallNextHookEx(this, nCode, wParam, lParam);
    }

    protected override bool ReleaseHandle()
    {
        return NativeMethods.UnhookWindowsHookEx(this.handle);
    }
}

public abstract class WindowsHook : IDisposable
{
    private SafeHookHandle hhk;
    private HookProc lpfn;

    protected WindowsHook(HookType idHook, HookScope scope)
    {
        this.lpfn = this.OnWindowsHook;

        switch(scope)
        {
            case HookScope.LowLevelGlobal:
                IntPtr moduleHandle = NativeMethods.GetModuleHandle(null);
                this.hhk = SafeHookHandle.SetWindowsHook(idHook, this.lpfn, moduleHandle, 0U);
                return;
            default:
                throw new InvalidEnumArgumentException("scope", (int)scope, typeof(HookScope));
        }
    }

    protected virtual IntPtr OnWindowsHook(int nCode, IntPtr wParam, IntPtr lParam)
    {
        return this.hhk.CallNextHook(nCode, wParam, lParam);
    }

    public void Dispose()
    {
        this.Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if(disposing)
        {
            if(this.hhk != null) { this.hhk.Dispose(); }
        }
    }
}

public class LowLevelMouseHook : WindowsHook
{
    public event MouseEventHandler MouseWheel;

    public LowLevelMouseHook() : base(HookType.LowLevelMouseHook, HookScope.LowLevelGlobal) { }

    protected sealed override IntPtr OnWindowsHook(int nCode, IntPtr wParam, IntPtr lParam)
    {
        if(nCode == NativeConstants.HC_ACTION)
        {
            var msLLHookStruct = (NativeTypes.MSLLHOOKSTRUCT)Marshal.PtrToStructure(lParam, typeof(NativeTypes.MSLLHOOKSTRUCT));

            switch(wParam.ToInt32())
            {
                case NativeConstants.WM_MOUSEWHEEL:
                case NativeConstants.WM_MOUSEHWHEEL:
                    this.OnMouseWheel(new MouseEventArgs(Control.MouseButtons, 0, msLLHookStruct.pt.X, msLLHookStruct.pt.Y, (int)msLLHookStruct.mouseData >> 16));
                    break;
            }
        }

        return base.OnWindowsHook(nCode, wParam, lParam);
    }

    protected virtual void OnMouseWheel(MouseEventArgs e)
    {
        if(this.MouseWheel != null)
        {
            this.MouseWheel(this, e);
        }
    }
} 

示例用法:

using (LowLevelMouseHook hook = new LowLevelMouseHook())
{
    hook.MouseWheel += (sender, e) =>
    {
        Console.WriteLine(e.Delta);
    };
    Application.Run();
}

该代码提供了一个类 LowLevelMouseHook 和一个事件 MouseWheel，其行为类似于来自内置 Windows 窗体控件类的事件。

(此外，代码被拆分为一个抽象类 WindowsHooks 以与其他 Hook 一起使用，一个 SafeHookHandle 类以确保释放句柄和辅助类对于本地方法)

你应该看看SetWindowsHookEx和 CALLBACK LowLevelMouseProc了解这背后的技术。

---

此事件不仅限于您的应用程序，还会捕获表单外的鼠标，因此它也适用于您不能使用本地事件的操作。