我的本机代码中包含以下内容:
typedef void (__stdcall * HandlerCallBack)(float);
class ASSIMP_API NewProgressHandler : public ProgressHandler
{
HandlerCallBack CallBack;
public:
bool Update(float percentage = -1.f){
if (CallBack) CallBack (percentage);
return true;
}
void SetCallBack (HandlerCallBack callback) {
CallBack = callback;
}
};
void Importer::SetProgressHandlerCallBack (HandlerCallBack CallBack) {
NewProgressHandler* pNewHandler = new NewProgressHandler ();
pNewHandler->SetCallBack (CallBack);
ProgressHandler* pHandler = pNewHandler;
SetProgressHandler (pHandler);
}
我需要打电话
SetProgressHandlerCallBack (HandlerCallBack CallBack)
从c#代码,所以我做了以下:
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate void HandlerCallBack([MarshalAs(UnmanagedType.R4)]float percent);
[DllImport("my.dll")]
public static extern void SetProgressHandlerCallBack ([MarshalAs(UnmanagedType.FunctionPtr)]
HandlerCallBack callBack);
public void AssimpCallBack ([MarshalAs(UnmanagedType.R4)]float percent) {
Debug.Log (percent);
}
void SomeFunction () {
HandlerCallBack cb = new HandlerCallBack (AssimpCallBack);
SetProgressHandlerCallBack (cb);
}
但我得到一个例外,
SetProgressHandlerCallBack
at (wrapper managed-to-native)
ModellInstantiator:SetProgressHandlerCallBack
(ModellInstantiator/HandlerCallBack)
我无法弄清楚我错过了什么.
最佳答案 在您上面的代码中,您显示的SetProgressHandlerCallback函数如下所示:
void Importer::SetProgressHandlerCallBack(...) { ... }
这有两个问题,这两个问题都可以用一个简单的最小完整可验证示例来解释,我创建了一个新的Visual Studio解决方案,包含一个C#(WinForms)项目和一个C Dll(非托管而不是C/C++LI).
在DLL(dllmain.cpp)中,我放置了以下代码:
typedef void (__stdcall *HandlerCallBack)(float);
extern "C" {
// extern "C" ignored for C++ classes
class __declspec(dllexport) TestClass
{
public:
static void CallMeBack(HandlerCallBack callback)
{
callback(1.0f);
}
};
void __declspec(dllexport) CallRightBack(HandlerCallBack callback)
{
TestClass::CallMeBack(callback);
}
}
您可以看到与您正在使用的回调签名匹配的回调签名,以及静态类方法和导出的函数.构建它,启动Visual Studio命令提示符并运行
dumpbin /exports <dllname>.dll
这为您提供了DLL中的导出函数,如下所示:
(Trimmed to just show what we care about)
ordinal hint RVA name
1 0 00011082 ??4TestClass@@QEAAAEAV0@$$QEAV0@@Z = @ILT+125(??4TestClass@@QEAAAEAV0@$$QEAV0@@Z)
2 1 000110E1 ??4TestClass@@QEAAAEAV0@AEBV0@@Z = @ILT+220(??4TestClass@@QEAAAEAV0@AEBV0@@Z)
3 2 00011069 ?CallMeBack@TestClass@@SAXP6AXM@Z@Z = @ILT+100(?CallMeBack@TestClass@@SAXP6AXM@Z@Z)
4 3 00011014 CallRightBack = @ILT+15(CallRightBack)
您会注意到常规全局函数是以未修饰的名称导出的,但静态方法是使用修饰(受损)名称导出的.
现在让我们为C#项目添加一些代码,看看为什么这会成为一个问题.添加2个按钮(button1和button22).在表单中,我添加了以下代码:
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
delegate void HandlerCallbackDelegate(float value);
[DllImport("CppDllTestProj.dll")]
static extern void CallRightBack([MarshalAs(UnmanagedType.FunctionPtr)]HandlerCallbackDelegate callback);
[DllImport("CppDllTestProj.dll")]
static extern void CallMeBack([MarshalAs(UnmanagedType.FunctionPtr)]HandlerCallbackDelegate callback);
HandlerCallbackDelegate callbackDel;
// in the designer associated with button1
private void button1_Click(object sender, EventArgs e)
{
if (this.callbackDel == null)
{
this.callbackDel = new HandlerCallbackDelegate(this.Callback);
}
CallRightBack(callbackDel);
}
// in the designer associated with button2
private void button2_Click(object sender, EventArgs e)
{
if (this.callbackDel == null)
{
this.callbackDel = new HandlerCallbackDelegate(this.Callback);
}
CallMeBack(callbackDel);
}
void Callback(float value)
{
MessageBox.Show(value.ToString());
}
编译,将dll复制到C#项目的构建目录中,然后运行.单击button1,调用回调,并显示消息框.单击按钮2,程序崩溃,但异常:
Unable to find an entry point named ‘CallMeBack’ in DLL ‘CppDllTestProj.dll’.
at ScratchApp.Form1.CallMeBack(HandlerCallbackDelegate callback)
at ScratchApp.Form1.button2_Click(Object sender, EventArgs e) in Form1.cs:line 49
无法找到名为“CallMeBack”的入口点意味着它无法在该DLL中找到具有该名称的函数.如果我现在将C#测试应用程序中的CallMeBack定义更改为:
[DllImport("CppDllTestProj.dll", EntryPoint="?CallMeBack@TestClass@@SAXP6AXM@Z@Z")]
static extern void CallMeBack([MarshalAs(UnmanagedType.FunctionPtr)]HandlerCallbackDelegate callback);
重新编译并重新启动,现在两个按钮都能正常工作. (你的受损/装饰名称可能看起来不同.使用从dumpbin获得的任何值.)
这个问题的根源是C类和类成员3忽略了extern“c”存储类说明符.
修复上述内容后,您将遇到的另一个问题是此代码:
void SomeFunction () {
HandlerCallBack cb = new HandlerCallBack (AssimpCallBack);
SetProgressHandlerCallBack (cb);
}
您将注意到,当控件从对SetProgressHandlerCallBack的调用返回时,cb变为可用于垃圾收集.一旦该委托被垃圾收集,任何回调都将失败.壮观.
1技术上我用于所有测试的项目相同,但我每次都清除代码.
我知道,有两个名字.
3Source:Is it possible to export a C++ member method with C linkage in a DLL?