Objective C使用JNI调用Java方法 [英] Objective C calling Java methods using JNI

问题描述

有人可以告诉我如何从Objective C调用Java方法。

Can someone show me how to call a Java method from Objective C.

更详细地说，这实际上是我想做的事情

In more detail this is actually what I would like to do

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。

1) Have first call from the java side to the objective C. during this call I would like to get a reference to the java object.

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。

2) Later down the line I would like Objective C to use the reference got in the previous step to call Java methods.

谢谢

推荐答案

以下似乎有效。它基于上面关于C示例和此链接的注释。

The following seems to work. It is based on the above comment on following the C examples and this link.

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

正如链接所说，不为env创建全局变量而是创建jvm的全局变量，同时创建对类的全局引用。

As the link says do not create a global variable for the env instead create a global variable of the jvm, also create a global reference to your class.

以下是我实现步骤1的方法：

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

Here is how I implement the step 1 : " 1) Have first call from the java side to the objective C. during this call I would like to get a reference to the java object. "

首先在头文件中声明全局变量

First declare global variable in the header file for

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

Next in the call that comes from the Java side to the Objective C set the values for these variables

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;
    }       
}

这是我从中获取代码的链接班级

Here is the link from where I got the code for the class

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

现在第二步

2后来我希望Objective C使用上一步中获得的引用来调用Java方法

" 2) Later down the line I would like Objective C to use the reference got in the previous step to call Java methods "

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。

To call from Objective C back to Java you need to make sure that the call is done on the same thread by which Java called Objective C, so here is the code.

-(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);

}

希望这会有所帮助。

这篇关于Objective C使用JNI调用Java方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！