问题描述
我需要使用接口"在 Java 中实现回调函数.我已将应用程序部分编写为 MyJavaFunction(int size, m_GetSizeInterface);
I need to implement callback function in Java using "interface". I have wrote the application part as MyJavaFunction(int size, m_GetSizeInterface);
m_GetSizeInterface 是一个包含回调函数 GetSize 的接口.此 GetSize 方法在应用程序中被覆盖.在 JNI 中,我需要调用具有原型的 CPP 函数 int MyCPPFunction(int size, int (*callback)(int* ID));
m_GetSizeInterface is an Interface which contains the callback function GetSize. This GetSize method is override in the application. In JNI I need to call a CPP function having prototype int MyCPPFunction(int size, int (*callback)(int* ID));
如何将此 GetSize 作为参数传递给 JNI 中的 MyCPPFunction?请帮忙
How can I pass this GetSize as parameter to MyCPPFunction in JNI? Please help
public int GetSize (m_SizeClass arg0)
{
g_size = arg0.size;
return 0;
}
推荐答案
这里的复杂之处在于您想要调用本机 C++ 代码,而您又想要调用 Java 方法.这实际上有点棘手.
The complication here is that you want to invoke native C++ code which you, in turn, want to invoke a java method. This is actually a bit tricky.
需要创建一个JNI C++函数供java调用,并匹配一个C++函数MyCPPFunction 回调签名.后者将充当调用 java 方法的包装器.
You need to create a JNI C++ function for java to call, and a C++ function matching the MyCPPFunction callback signature. The latter will act as a wrapper to call the java method.
因为包装器需要有关 JNI 环境的信息,而这些信息不能由参数提供(以免破坏签名),所以您创建了一些全局变量来保存它:
Because the wrapper will need information about the JNI environment, which cannot be provided by parameters (lest we ruin the signature) you create a few global variables to hold it:
jobject g_getSizeIface;
jmethodID g_method;
JNIEnv *g_env;
java 将调用的 C++ 函数如下:
The C++ function which java will call is the following:
JNIEXPORT void JNICALL Java_ClassName_MyCPPFunction
(JNIEnv *env, jint size, jobject getSizeInterface)
{
jclass objclass = env->GetObjectClass(getSizeInterface);
jmethodID method = env->GetMethodID(objclass, "GetSize", "(m_SizeClass)I");
if(methodID == 0){
std::cout << "could not get method id!" << std::endl;
return;
}
g_method = method;
g_getSizeIface = getSizeInterface;
g_env = env
MyCPPFunction(size, WrapperFunc);
}
包装函数是这样的:
int WrapperFunc(int *id)
{
jint retval;
//marshalling an int* to a m_SizeClass boogy-woogy.
...
g_env->ExceptionClear();
retval = g_env->CallIntMethod(g_getSizeIface, g_method,
/*marshalled m_SizeClass*/);
if(g_env->ExceptionOccurred()){
//panic! Light fires! The British are coming!!!
...
g_env->ExceptionClear();
}
return rvalue;
}
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