.NET 4.0的ICustomQueryInterface新特性
在.NET Framework v4.0發(fā)布的新功能中，在名字空間System.Runtime.InteropServices新增加了一個叫做ICustomQueryInterface的Interface, 顧名思義，這個Interface的功能就是使得用戶可以自己控制QueryInterface這個COM最常用的函數(shù)的行為。在v4.0以前，所有作用于托管組件上的QI行為，都是由CLR內(nèi)部的IUnkown:QueryInterface控制的，比如，如果你QI著名的IDispatch接口時，你得到的永遠都是CLR提供的那個IDispatch，諸如此類的還有IMarshal/IProvideClassInfo等一些常用的Interface。如果你非常希望用自己的IDispatch實現(xiàn)來替換clr提供的實現(xiàn)，那么恭喜你，ICustomQueryInterface就是為你而生的！當然，ICustomQueryInterface所帶來的，不僅僅是簡單的Interface替換，它甚至可以使得Aggregate托管組件也成為現(xiàn)實，wow，如果你了解Aggregation的話，一定會因此而雀躍不已的。我會在另一篇文章中通過例程給大家做一個詳細的介紹。
讓我們來看看這個ICustomQueryInterface的定義吧：
1: public interface ICustomQueryInterface2: {3: CustomQueryInterfaceResult GetInterface([In]ref Guid iid, out IntPtr ppv);4: }5:
是的，就是這么簡單，就一個GetInterface方法，再仔細看看它的方法參數(shù)，是不是和c++里面的QueryInterface有點神似啊。哈哈，其實你可以把它理解成QueryInterface的托管實現(xiàn)也無妨啊！不過它還有個小小的功能，就是如果自己不想處理這個QI，就返回NotHandled, clr看到這個返回值，就會調(diào)用自己的QI實現(xiàn)來幫你處理這個請求，爽吧。
讓我們來看看有了這個Interface之后clr內(nèi)部關于QI的處理流程圖吧：
.NET 4.0新特性：ICustomQueryInterface
從這個圖上我們可以看到，除了不能處理對IUnknown的QI請求(要求別太高嘛)，其他統(tǒng)統(tǒng)OK！
理論一大堆了，來實戰(zhàn)一下。
看看我們的托管組件的實現(xiàn)
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 ICQ
9: {
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 IA
19: {
20: int FuncA();
21: }
22:
23: [Guid("22220400-0000-0000-C000-000000001149")]
24: [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
25: public interface IB
26: {
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, IB
35: {
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 Functions
76: public void slot2() { }
77: public void slot3() { }
78: public void slot4() { }
79: #endregion
80: }
81:
82: }
83:
這里稍微做個解釋，GetInterface的返回值如果是CustomQueryInterfaceResult.Failed，意思是QI失敗。CustomQueryInterfaceResult.NotHandled意思是讓clr去處理這個請求，CustomQueryInterfaceResult.Handled是告訴clr，已經(jīng)處理好了，指針值保存在intf里面，直接返回給用戶就可以了。
再來看看我們的客戶端
- 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**)&hresult);
- 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);
再來看看我們的輸出結果。
- Scenario 1: QI IDispatch interface, Expected the Custom IDispatch interface
- This is Interface ICQ, not the IDispatch!!!
- Return value of GetTypeInfoCount is 2008
- Scenario 2: QI iA interface, Expected failed
- Failed to QI IA with error code 7d8
- Scenario 3: QI IB interface interface, Expected the IB interface
- This is Interface IB!!!
以上就介紹了.NET 4.0的命名空間中的ICustomQueryInterface新特性。
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