动态加载DLL需要使用Windows API函数:LoadLibrary、GetProcAddress以及FreeLibrary。我们可以使用DllImport在C#中使用这三个函数。
[DllImport("Kernel32")]
public static extern int GetProcAddress(int handle, String funcname);
[DllImport("Kernel32")]
public static extern int LoadLibrary(String funcname);
[DllImport("Kernel32")]
public static extern int FreeLibrary(int handle);
当我们在C++中动态调用Dll中的函数时,我们一般的方法是:
假设DLL中有一个导出函数,函数原型如下:
BOOL __stdcall foo(Object &object, LPVOID lpReserved);
1、首先定义相应的函数指针:
typedef BOOL (__stdcall *PFOO)(Object &object, LPVOID lpReserved);
2、调用LoadLibrary加载dll:
HINSTANCE hInst = ::LoadLibraryW(dllFileName);
3、调用GetProcAddress函数获取要调用函数的地址:
PFOO foo = (PFOO)GetProcAddress(hInst,"foo");
if(foo == NULL)
{
FreeLibrary(hInst);
return false;
}
4、调用foo函数:
BOOL bRet = foo(object,(LPVOID)NULL);
5、使用完后应释放DLL:
FreeLibrary(hInst);
那么在C#中应该怎么做呢?方法基本上一样,我们使用委托来代替C++的函数指针,通过.NET Framework 2.0新增的函数GetDelegateForFunctionPointer来得到一个委托的实例:
下面封装了一个类,通过该类我们就可以在C#中动态调用Dll中的函数了:
public class DLLWrapper { ///<summary> /// API LoadLibrary ///</summary> [DllImport("Kernel32")] public static extern int LoadLibrary(String funcname); ///<summary> /// API GetProcAddress ///</summary> [DllImport("Kernel32")] public static extern int GetProcAddress(int handle, String funcname); ///<summary> /// API FreeLibrary ///</summary> [DllImport("Kernel32")] public static extern int FreeLibrary(int handle); ///<summary> ///通过非托管函数名转换为对应的委托, by jingzhongrong ///</summary> ///<param name="dllModule">通过LoadLibrary获得的DLL句柄</param> ///<param name="functionName">非托管函数名</param> ///<param name="t">对应的委托类型</param> ///<returns>委托实例,可强制转换为适当的委托类型</returns> public static Delegate GetFunctionAddress(int dllModule, string functionName, Type t) { int address = GetProcAddress(dllModule, functionName); if (address == 0) return null; else return Marshal.GetDelegateForFunctionPointer(new IntPtr(address), t); } ///<summary> ///将表示函数地址的IntPtr实例转换成对应的委托, by jingzhongrong ///</summary> public static Delegate GetDelegateFromIntPtr(IntPtr address, Type t) { if (address == IntPtr.Zero) return null; else return Marshal.GetDelegateForFunctionPointer(address, t); } ///<summary> ///将表示函数地址的int转换成对应的委托,by jingzhongrong ///</summary> public static Delegate GetDelegateFromIntPtr(int address, Type t) { if (address == 0) return null; else return Marshal.GetDelegateForFunctionPointer(new IntPtr(address), t); } } |