SetWinEventHook 每次应用运行仅命中一次回调

Question

我有这个类，当 CTRL + ALT + DEL 屏幕可见时侦听。当我运行我的应用程序时，它只工作一次，然后回调再也不会命中。偶尔它似乎会导致内存泄漏，给我一个System.AccessViolationException。我知道这个异常与此钩子有关，因为当我删除钩子代码时，它永远不会引发此异常。

我做错了什么？为什么它只执行一次回调？

public static void StartListeningForDesktopSwitch()
{
SetWinEventHook(EVENT_SYSTEM_DESKTOPSWITCH, EVENT_SYSTEM_DESKTOPSWITCH,
IntPtr.Zero, EventCallback, 0, 0, WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNTHREAD);
}
public static void EventCallback(IntPtr hWinEventHook, uint eventType,
IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
{
//do stuff when secure desktop is shown or hidden
Log.LogEvent("Info", "Secure Desktop Event", "", "", null);
}
public delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType,
IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime);

[DllImport("user32.dll")]
static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax, IntPtr
hmodWinEventProc, WinEventDelegate lpfnWinEventProc, uint idProcess,
uint idThread, uint dwFlags);
const uint WINEVENT_OUTOFCONTEXT = 0x0000;
const uint WINEVENT_SKIPOWNTHREAD = 0x0001;
const uint EVENT_SYSTEM_DESKTOPSWITCH = 0x0020;

我从 Main(( 调用这个静态类，如下所示：

WindowEventHook.StartListeningForDesktopSwitch();

Answer 1

你是如何使用外部变量的？

尝试将回调存储在静态变量中，以防止其被 GC 处理。喜欢这个：

public static class WindowEventHook
{
private static readonly WinEventDelegate callback = EventCallback;
public static void StartListeningForDesktopSwitch()
{
SetWinEventHook(EVENT_SYSTEM_DESKTOPSWITCH, EVENT_SYSTEM_DESKTOPSWITCH,
IntPtr.Zero, callback, 0, 0, WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNTHREAD);
}
...
}