无效的JNI引用（从c ++调用Java方法）

Question

我遇到了从c ++启用GPS定位的调用问题。我用SWIG生成了JNI包装器。 logcat说：

01-02 17:14:03.816: D/dalvikvm(6165): Trying to load lib /data/data/com.example.swig/lib/libcppinterface.so 0x44e7ebf0
01-02 17:14:03.976: D/dalvikvm(6165): Added shared lib /data/data/com.example.swig/lib/libcppinterface.so 0x44e7ebf0
01-02 17:14:04.886: W/dalvikvm(6165): JNI WARNING: 0x44e8bb48 is not a valid JNI reference
01-02 17:14:04.886: W/dalvikvm(6165):              in Lcom/example/swig/cpplib/cppinterfaceJNI;.LocationSpotter_refresh (JLcom/example/swig/cpplib/LocationSpotter;)V (CallVoidMethodV)
01-02 17:14:04.886: I/dalvikvm(6165): "main" prio=5 tid=1 RUNNABLE
01-02 17:14:04.886: I/dalvikvm(6165):   | group="main" sCount=0 dsCount=0 s=N obj=0x4001d8e0 self=0xccb0
01-02 17:14:04.886: I/dalvikvm(6165):   | sysTid=6165 nice=0 sched=0/0 cgrp=default handle=-1345026008
01-02 17:14:04.886: I/dalvikvm(6165):   | schedstat=( 226108400 549900071 66 )
01-02 17:14:04.886: I/dalvikvm(6165):   at com.example.swig.cpplib.cppinterfaceJNI.LocationSpotter_refresh(Native Method)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.example.swig.cpplib.LocationSpotter.refresh(LocationSpotter.java:56)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.example.swig.MainActivity.onCreate(MainActivity.java:50)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.os.Handler.dispatchMessage(Handler.java:99)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.os.Looper.loop(Looper.java:123)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.main(ActivityThread.java:4627)
01-02 17:14:04.896: I/dalvikvm(6165):   at java.lang.reflect.Method.invokeNative(Native Method)
01-02 17:14:04.896: I/dalvikvm(6165):   at java.lang.reflect.Method.invoke(Method.java:521)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-02 17:14:04.896: I/dalvikvm(6165):   at dalvik.system.NativeStart.main(Native Method)
01-02 17:14:04.906: E/dalvikvm(6165): VM aborting

我用这行来触发来自Java的调用：

LocationSpotter.getLocationSpotter().refresh();

getLocationSpotter（）在c ++中触发此代码创建一个jobject（jSpotter）：

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);

jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID construct = env->GetMethodID(clazz, "<init>", "()V");

jSpotter = env->NewObject(clazz, construct);

并且在方法refresh（）之后触发此代码，导致应用程序崩溃：

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);

jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID refresh = env->GetMethodID(clazz, "refresh", "()V");

env->CallVoidMethod(jSpotter, refresh); // The line where the crash happens

我还需要提一下，我在JNI_OnLoad函数中启动了“cachedJVM”。希望有人可以帮助我，谢谢

修改

工作代码：

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);

jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID construct = env->GetMethodID(clazz, "<init>", "()V");

jSpotter = env->NewObject(clazz, construct);

jSpotter = env->NewGlobalRef(jSpotter);

Answer 1

您需要使用返回的jSpotter引用创建新的全局引用。您当前使用的引用是当前帧的本地引用，并且将超出范围（可能在您使用DetachCurrentThread（）时）。

您需要致电env->NewGlobalRef(jSpotter)或env->NewWeakGlobalRef(jSpotter)（两者都有相应的free个功能）并使用返回的引用。

修改

以下是正确附加/分离处理的示例（假设您不需要该线程进行进一步的Java操作）：

  JNIEnv* env;
  JavaVM* jvm = AndroidLocationSpotter::cachedJVM;

  int attached = jvm->GetEnv((void *)&env, JNI_VERSION_1_4) == JNI_OK;
  if (!attached) {
    if (jvm->AttachCurrentThread((void *)&env, NULL) != JNI_OK) {
      // Attach failed, handle error condition
      return;
    }
  }

  // Pushing a frame ensures proper cleanup of any local references you might generate
  // in your JNI code, e.g. with NewLocalRef (optional)                                                                                                                                                                                
  if (env->PushLocalFrame(16) < 0) {
    // Handle failed frame push error
  }
  else {
    // example local reference generation: ref2 = env->NewLocalRef(ref);

    //
    // Perform your primary Java operations here
    //

    env->PopLocalFrame(NULL);
  }

  if (!attached) {
    jvm->DetachCurrentThread();
  }