.NET 4.0 Interop新特性ICustomQueryInterface
在.NET Framework v4.0发布的新功能中,在名字空间System.Runtime.InteropServices新增加了一个叫做ICustomQueryInterface的Interface, 顾名思义,这个Interface的功能就是使得用户可以自己控制QueryInterface这个COM最常用的函数的行为。在v4.0以前,所有作用于托管组件上的QI行为,都是由CLR内部的IUnkown:QueryInterface控制的,比如,如果你QI著名的IDispatch接口时,你得到的永远都是CLR提供的那个IDispatch,诸如此类的还有IMarshal/IProvideClassInfo等一些常用的Interface。如果你非常希望用自己的IDispatch实现来替换clr提供的实现,那么恭喜你,ICustomQueryInterface就是为你而生的!当然,ICustomQueryInterface所带来的,不仅仅是简单的Interface替换,它甚至可以使得Aggregate托管组件也成为现实,wow,如果你了解Aggregation的话,一定会因此而雀跃不已的。我会在另一篇文章中通过例程给大家做一个详细的介绍。
让我们来看看这个Interface的定义吧
1: public interface ICustomQueryInterface2: {3: CustomQueryInterfaceResult GetInterface([In]ref Guid iid, out IntPtr ppv);4: }5:
是的,就是这么简单,就一个GetInterface方法,再仔细看看它的方法参数,是不是和c++里面的QueryInterface有点神似啊。哈哈,其实你可以把它理解成QueryInterface的托管实现也无妨啊!不过它还有个小小的功能,就是如果自己不想处理这个QI,就返回NotHandled, clr看到这个返回值,就会调用自己的QI实现来帮你处理这个请求,爽吧。
让我们来看看有了这个Interface之后clr内部关于QI的处理流程图吧(画的是英文版,烦请大家将就一下啦,没装viso,画图超级累啊!!!!)
从这个图上我们可以看到,除了不能处理对IUnknown的QI请求(要求别太高嘛),其他统统OK!
理论一大堆了,来实战一下。
看看我们的托管组件的实现
1: using System;
2: using System.Runtime.InteropServices;
3:4: namespace States
5: {6: [Guid("00020400-0000-0000-C000-000000001147")]
7: [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]8: public interface ICQ9: {10: int func();
11: void slot2();
12: void slot3();
13: void slot4();
14: }15:16: [Guid("11120400-0000-0000-C000-000000001148")]
17: [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]18: public interface IA19: {20: int FuncA();
21: }22:23: [Guid("22220400-0000-0000-C000-000000001149")]
24: [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]25: public interface IB26: {27: int FuncB();
28: }29:30:31:32: [Guid("00020400-0000-0000-C000-000000001150")]
33: [ClassInterface(ClassInterfaceType.None)]34: public class StatesComServer : ICustomQueryInterface, ICQ, IA, IB35: {36: public readonly Guid IID_IA = new Guid("11120400-0000-0000-C000-000000001148");37:38: public CustomQueryInterfaceResult GetInterface([In]ref Guid iid, out IntPtr intf)39: {40: if (iid == WellKnownGuids.IID_IDispatch)
41: {42: intf = Marshal.GetComInterfaceForObject(this, typeof(ICQ), CustomQueryInterfaceMode.Ignore);43: return CustomQueryInterfaceResult.Handled;
44: }45:46: if (iid == IID_IA)
47: {48: intf = IntPtr.Zero;49: return CustomQueryInterfaceResult.Failed;
50: }51:52: intf = IntPtr.Zero;53: return CustomQueryInterfaceResult.NotHandled;
54: }55:56: public int func()57: {58: Console.WriteLine("This is Interface ICQ, not the IDispatch!!!");
59: return 2008;
60: }61:62: public int FuncA()63: {64: Console.WriteLine("This is Interface IA!!!");
65: return 3008;
66: }67:68: public int FuncB()69: {70: Console.WriteLine("This is Interface IB!!!");
71: return 4008;
72: }73:74:75: #region Empty Functions76: public void slot2() { }77: public void slot3() { }78: public void slot4() { }79: #endregion80: }81:82: }83:
这里有两个地方需要解释一下
1)对于ICQ这个接口,他实际上是作为自定义的IDispatch出现的,所以理论上应该他所有的函数声明应该和IDispatch保持一致,但是个人比较偷懒,毕竟这只是一个例程,主要是将如何使用ICustomQueryInterface这个接口,所以后三个方法的用途仅仅是为了保持ICQ的虚拟函数表(一共4个函数)和IDispatch保持一致,如果真的有人在客户端调IDispatch.Invoke(函数表中的第四个函数)的话,那调用必然会被重定向到ICQ.slot4,因为两个函数的参数声明完全不一样,AccessViolationException就无法避免了。
2)再讲一下GetInterface的返回值,如果是CustomQueryInterfaceResult.Failed,意思是QI失败。CustomQueryInterfaceResult.NotHandled意思是让clr去处理这个请求,CustomQueryInterfaceResult.Handled是告诉clr,已经处理好了,指针值保存在intf里面,直接返回给用户就可以了。
再来看看我们的客户端
IDispatch * pDisp = NULL;printf("Scenario 1: QI IDispatch interface, Expected the Custom IDispatch interface\n");
hresult = pUnknown->QueryInterface(IID_IDispatch, (void**)&pDisp);
UINT count = 0;hresult = pDisp->GetTypeInfoCount(&count);printf("Return value of GetTypeInfoCount is %d\n", count);
IA * pA = NULL;printf("Scenario 2: QI IA interface, Expected failed\n");
hresult = pUnknown->QueryInterface(IID_IA, (void**)&pA);
if (FAILED(hresult))
{printf("Failed to QI IA with error code %x\n", count);
}IB * pB = NULL;printf("Scenario 3: QI IB interface interface, Expected the IB interface\n");
hresult = pUnknown->QueryInterface(IID_IB, (void**)&pB);
long i = 0;
hresult = pB->FuncB(&i);
再来看看我们的输出结果。
Scenario 1: QI IDispatch interface, Expected the Custom IDispatch interfaceThis is Interface ICQ, not the IDispatch!!!
Return value of GetTypeInfoCount is 2008Scenario 2: QI iA interface, Expected failedFailed to QI IA with error code 7d8Scenario 3: QI IB interface interface, Expected the IB interfaceThis is Interface IB!!!
Published Monday, August 10, 2009 11:34 AM by SilverlightShanghai