Question

我需要创建一个RichTextBox子类，除了没有订阅UserPreferenceChanged之外，它在所有方面都是相同的。此事件导致我的应用挂起。我必须使用RichTextBox，并且无法将其交换为具有MultiLine = True的TextBox或其他类似的东西。

这是System.Windows.Forms.RichTextBox订阅的地方;

protected override void OnHandleCreated(EventArgs e)
{
    ...
    SystemEvents.UserPreferenceChanged += new UserPreferenceChangedEventHandler(this.UserPreferenceChangedHandler);
}

这是处理程序的签名;

private void UserPreferenceChangedHandler(object o, UserPreferenceChangedEventArgs e)

处理程序不是虚拟的，所以我无法覆盖它。处理程序是私有的，所以我不能做一个简单的 - = 来取消订阅。我已经研究过使用反射去除处理程序，但是我无法让它工作 - 这是我到目前为止所拥有的;

public partial class MyRichTextBox : RichTextBox
{
    ...

private void UnsubscribeUserPreferenceChanged()
{
    FieldInfo fieldInfo = typeof(SystemEvents).GetField("OnUserPreferenceChangedEvent", BindingFlags.NonPublic | BindingFlags.Static);
        // fieldInfo.ToString() = "System.Object.OnUserPreferenceChangedEvent"
    object eventObj = fieldInfo.GetValue(this);
        // eventInfo.ToString() = "System.Object"
    PropertyInfo propInfo = typeof(RichTextBox).GetProperty("Events", BindingFlags.NonPublic | BindingFlags.Instance);
        // propInfo.ToString() = "System.ComponentModel.EventHandlerList Events"
    EventHandlerList list = (EventHandlerList)propInfo.GetValue(this, null);
        // list.ToString() = "System.ComponentModel.EventHandlerList"
    ...

现在我可以打电话了;

list.RemoveHandler(eventObj, list[eventObj]);

并且没有例外，但我相信它会默默地失败，因为如果我试图以这样的方式访问该委托;

list[eventObj].ToString()

我得到一个NullReferenceException，因为EventHandlerList中没有这样的对象键。我在MyTextBox变得可见之后调用UnsubscribeUserPreferenceChanged（），因此处理程序应该在列表中，因为它是在OnHandleCreated中为RichTextBox添加的。

任何人都有关于如何取消订阅连接到超类中的私有事件处理程序的SystemEvent的任何指示？

Answer 1

一旦你知道方法名称，由于以下方便的CreateDelegate重载，这很容易：

==7042== Invalid read of size 1
==7042==    at 0x4045F71: ??? (in /tmp/.glamhkos (deleted))
==7042==    by 0xCFFFFFF: ???
==7042==    by 0xD68A04F: ???
==7042==    by 0xFFEFFFE3F: ???
==7042==  Address 0xd000002 is 0 bytes after a block of size 2 alloc'd
==7042==    at 0x4C2B1B6: memalign (vg_replace_malloc.c:760)
...
==7042==    by 0x4016E1: main (in /.../)


==7042== Invalid read of size 1
==7042==    at 0x4045F71: ??? (in /tmp/.glamhkos (deleted))
==7042==    by 0xD0017FF: ???
==7042==    by 0xD68C04F: ???
==7042==    by 0xFFEFFFE3F: ???
==7042==    by 0x1: ???
==7042==    by 0x7B23325: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
==7042==    by 0x7B2D9A6: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
==7042==    by 0x7C7DD40: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
==7042==    by 0x7C51383: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
==7042==    by 0x7C52A16: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
==7042==    by 0x7C6F553: ??? (in /usr/lib/x86_64-linux-gnu/libnvidia-glcore.so.352.79)
...
==7042==  Address 0xd001802 is 6,146 bytes inside a block of size 6,852,752 in arena "client"

所以有问题的代码可能是这样的：

public static Delegate CreateDelegate(
    Type type,
    object target,
    string method
)

Answer 2

您应该使用Type.GetEvent代替Type.GetField。

只有这样你才能在运行时删除它：

private void UnsubscribeuserPreferenceChanged()
{
    MethodInfo handler = typeof(RichTextBox).GetMethod("UserPreferenceChangedHandler", BindingFlags.Instance | BindingFlags.NonPublic);

    EventInfo evt = typeof(SystemEvents).GetEvent("UserPreferenceChanged", BindingFlags.Static | BindingFlags.Public);
    MethodInfo remove = evt.GetRemoveMethod(true);

    remove.Invoke(null, new object[]
    {
        Delegate.CreateDelegate(evt.EventHandlerType, null, handler)
    });
}

Answer 3

我找到了一种方法来解决此问题，方法是遍历所有订阅系统事件的对象，然后在执行期间取消订阅。这是上述方法和我发现的另一个代码的结合，该代码捕获了我应用程序中所有对象注册的所有系统事件

public static void UnsubscribeSystemEvents()
{         
     try
        {
            var handlers = typeof(SystemEvents).GetField("_handlers", BindingFlags.NonPublic | BindingFlags.Static).GetValue(null);
            var handlersValues = handlers.GetType().GetProperty("Values").GetValue(handlers);
            foreach (var invokeInfos in (handlersValues as IEnumerable).OfType<object>().ToArray())
                foreach (var invokeInfo in (invokeInfos as IEnumerable).OfType<object>().ToArray())
                {
                    var syncContext = invokeInfo.GetType().GetField("_syncContext", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(invokeInfo);
                    if (syncContext == null) 
                        throw new Exception("syncContext missing");
                    if (!(syncContext is WindowsFormsSynchronizationContext))
                        continue;
                    var threadRef = (WeakReference)syncContext.GetType().GetField("destinationThreadRef", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(syncContext);
                    if (!threadRef.IsAlive)
                        continue;
                    var thread = (System.Threading.Thread)threadRef.Target;
                    if (thread.ManagedThreadId == 1)
                            continue;  // Change here if you have more valid UI threads to ignore
                    var dlg = (Delegate)invokeInfo.GetType().GetField("_delegate", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(invokeInfo);
                    var handler = (UserPreferenceChangedEventHandler)Delegate.CreateDelegate(typeof(UserPreferenceChangedEventHandler), dlg.Target, dlg.Method.Name);
                    SystemEvents.UserPreferenceChanged -= handler;
                }
        }
        catch ()
        {                
            //trace here your errors
        }
    }

我可以使用Reflection取消订阅SystemEvent吗？

3 个答案: