Android 中Native方法是怎样调用的

是怎样调用的"/>

Android 中Native方法是怎样调用的

1.  Power.java--> find corresponding native cfile（查找对应的具体用C实现的C文件）

         android.os.Power.java -------- native file ---->.../jni/android_os_Power.c 2. in android_os_Power.c, you canfind:

static JNINativeMethod method_table[]=   // Native functiontable {
    {"acquireWakeLock", "(ILjava/lang/String;)V", (void*)acquireWakeLock},
    {"releaseWakeLock", "(Ljava/lang/String;)V", (void*)releaseWakeLock},
    {"setLastUserActivityTimeout", "(J)I",(void*)setLastUserActivityTimeout },
    {"setScreenState", "(Z)I", (void*)setScreenState },
    {"shutdown", "()V", (void*)android_os_Power_shutdown },
    { "reboot","(Ljava/lang/String;)V", (void*)android_os_Power_reboot },
}; int register_android_os_Power(JNIEnv *env)// function to register mapping tablefrom name to function
{
    returnAndroidRuntime::registerNativeMethods(
       env, "android/os/Power",
       method_table, NELEM(method_table));
}

3. in /framework/base/core/jni , a file named:AndroidRuntime.cpp    3.1) a global register function array            static const RegJNIRec gRegJNI[] =            {                      ...                      register_android_os_Power,           }    3.2) Register native function process                   int AndroidRuntime::startReg(JNIEnv* env)           or                  Java_com_android_internal_util_WithFramework_registerNatives(...)           or                 Java_LoadClass_registerNatives(....)                   ---> register_jni_procs(gRegJNI, NELEM(gRegJNI),env)                           ---> foreach(member of gRegJNI) call register_XXX_XXX_XXX..XXX()  //so here register_android_os_power() will becalled                                   ---> AndroidRuntime::registerNativeMethods(env, class_namelike "android/os/Power", method table like method_table,size)                                          ---> jniRegisterNativeMethods(env, className,gMethods, numMethods)                                                   -->pEnv->RegisterNatives(env, clazz, gMethods,numMethods) ;                                                        --> foreach(method) calldvmRegisterJNIMethod(ClassObject* clazz, const char*methodName,                                                                                                                                      constchar* signature, void* fnPtr)                                                               -->   calldvmSetNativeFunc(method, dvmCallSynchronizedJNIMethod, fnPtr); //for sycn method                                                                   or                                                                       call dvmSetNativeFunc(method, dvmCallJNIMethod,fnPtr);                                                                      -->   ((Method*)method)->insns = insns; // set actual codespace to be executed for a native function        4.calling a native method ( JNI method)    void dvmPlatformInvoke(void* pEnv,ClassObject* clazz, int argInfo, int argc,
    const u4*argv, const char* shorty, void* func, JValue*pReturn)    dvmCallMethod() /dvmInvokeMethod     --->    if(dvmIsNativeMethod(method))         {
                  (*method->nativeFunc)(self->curFrame,&retval, method, self);
       }