Objective C使用JNI调用Java方法

Question

有人可以告诉我如何从Objective C调用Java方法.

更详细地说,这实际上是我想要做的

1)首先从java端调用目标C.在此调用期间,我想获得对java对象的引用.

2)稍后我希望Objective C使用上一步中获得的引用来调用Java方法.

谢谢

Answer 1

以下似乎有效.它基于以上关于C示例和此链接的注释.

http://urlgrey.net/?p=121

正如链接所说,不要为env创建全局变量而是创建jvm的全局变量,也要创建对类的全局引用.

以下是我实现步骤1的方法:"1)首先从java端调用目标C.在此调用期间,我想获得对java对象的引用."

首先在头文件中声明全局变量

1)jvm:

JavaVM *jvm;

2)Java类:

jclass smartCallbackClass;

3)java对象:

jobject smartCallbackObject;

接下来,在Java端到Objective C的调用中,设置这些变量的值

1)对于JVM:

(*env)->GetJavaVM(env, &jvm);

2)对象:

smartCallbackObject = (*env)->NewGlobalRef(env, obj);

3)对于班级:

if (smartCallbackClass == NULL) {
    jclass localRefCls = (*env)->FindClass(env,"com/studyisland/nativelibs/smart/responsesdk/interfaces/thin/SMARTResponseThinClient"); 
    if (localRefCls == NULL) {
        NSLog(@"Unable to create a JNI Java Class reference \n");
    }
    //Create a global reference for JNI Java class
    smartCallbackClass = (*env)->NewGlobalRef(env,localRefCls);

    //Delete the local reference as it is no longer needed
    (*env)->DeleteLocalRef(env, localRefCls);

    //Is the global reference created successfully?
    if (smartCallbackClass == NULL) {
        NSLog(@"Unable to create JNI Java class reference \n");
        return 0;
    }       
}

这是我从中获取该类代码的链接

http://java.sun.com/docs/books/jni/html/refs.html

现在第二步

"2)稍后我希望Objective C使用上一步中获得的引用来调用Java方法"

要从Objective C调用回Java,你需要确保调用是在Java调用Objective C的同一个线程上完成的,所以这里是代码.

-(void)classFailedToStop:(SMARTResponseCallBackEventArg*)anArg{
    JNIEnv *env;
    int attach = (*jvm)->AttachCurrentThread(jvm, (void**)&env, NULL);
    if(attach == 0){
        (*jvm)->GetEnv(jvm, (void**)&env, JNI_VERSION_1_4);
        jmethodID method = (*env)->GetMethodID(env, smartCallbackClass, "callback_onStopClassFailed", "()V");
        (*env)->CallVoidMethod(env, smartCallbackObject, method);
    }
    (*jvm)->DetachCurrentThread(jvm);

}

希望这可以帮助.