Created a java wrapper for the callback OnAddTrack to PeerConnection.Observer

webrtc/api/android/jni/peerconnection_jni.cc

Index: webrtc/api/android/jni/peerconnection_jni.cc
diff --git a/webrtc/api/android/jni/peerconnection_jni.cc b/webrtc/api/android/jni/peerconnection_jni.cc
index 7012fc355a3f24257abf2326d918ed41e173ab9c..1a2c6e7eee4cb73196be2ecaf2ad9a8db1057b4f 100644
--- a/webrtc/api/android/jni/peerconnection_jni.cc
+++ b/webrtc/api/android/jni/peerconnection_jni.cc
@@ -173,18 +173,20 @@ class PCOJava : public PeerConnectionObserver {
       : j_observer_global_(jni, j_observer),
         j_observer_class_(jni, GetObjectClass(jni, *j_observer_global_)),
         j_media_stream_class_(jni, FindClass(jni, "org/webrtc/MediaStream")),
-        j_media_stream_ctor_(GetMethodID(
-            jni, *j_media_stream_class_, "<init>", "(J)V")),
+        j_media_stream_ctor_(
+            GetMethodID(jni, *j_media_stream_class_, "<init>", "(J)V")),
         j_audio_track_class_(jni, FindClass(jni, "org/webrtc/AudioTrack")),
-        j_audio_track_ctor_(GetMethodID(
-            jni, *j_audio_track_class_, "<init>", "(J)V")),
+        j_audio_track_ctor_(
+            GetMethodID(jni, *j_audio_track_class_, "<init>", "(J)V")),
         j_video_track_class_(jni, FindClass(jni, "org/webrtc/VideoTrack")),
-        j_video_track_ctor_(GetMethodID(
-            jni, *j_video_track_class_, "<init>", "(J)V")),
+        j_video_track_ctor_(
+            GetMethodID(jni, *j_video_track_class_, "<init>", "(J)V")),
         j_data_channel_class_(jni, FindClass(jni, "org/webrtc/DataChannel")),
-        j_data_channel_ctor_(GetMethodID(
-            jni, *j_data_channel_class_, "<init>", "(J)V")) {
-  }
+        j_data_channel_ctor_(
+            GetMethodID(jni, *j_data_channel_class_, "<init>", "(J)V")),
+        j_rtp_receiver_class_(jni, FindClass(jni, "org/webrtc/RtpReceiver")),
+        j_rtp_receiver_ctor_(
+            GetMethodID(jni, *j_rtp_receiver_class_, "<init>", "(J)V")) {}
 
   virtual ~PCOJava() {
     ScopedLocalRefFrame local_ref_frame(jni());
@@ -374,6 +376,23 @@ class PCOJava : public PeerConnectionObserver {
     CHECK_EXCEPTION(jni()) << "error during CallVoidMethod";
   }
 
+  void OnAddTrack(
+      rtc::scoped_refptr<RtpReceiverInterface> receiver,
+      std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams) override {
+    ScopedLocalRefFrame local_ref_frame(jni());
+    jobject j_rtp_receiver = jni()->NewObject(
+        *j_rtp_receiver_class_, j_rtp_receiver_ctor_, (jlong)receiver.get());
+    CHECK_EXCEPTION(jni()) << "error during NewObject";

[Taylor Brandstetter, 2016/11/17 23:02:53]

Need to call receiver->AddRef() after this, like in nativeGetReceivers.

[Zhi Huang, 2016/11/18 02:22:11]

Good catch! This could be a potential problem.

+
+    jobjectArray j_stream_array = ToJavaMediaStreamArray(jni(), streams);
+    jmethodID m =
+        GetMethodID(jni(), *j_observer_class_, "onAddTrack",
+                    "(Lorg/webrtc/RtpReceiver;[Lorg/webrtc/MediaStream;)V");
+    jni()->CallVoidMethod(*j_observer_global_, m, j_rtp_receiver,
+                          j_stream_array);
+    CHECK_EXCEPTION(jni()) << "Error during CallVoidMethod";
+  }
+
   void SetConstraints(ConstraintsWrapper* constraints) {
     RTC_CHECK(!constraints_.get()) << "constraints already set!";
     constraints_.reset(constraints);
@@ -423,6 +442,23 @@ class PCOJava : public PeerConnectionObserver {
     return java_candidates;
   }
 
+  jobjectArray ToJavaMediaStreamArray(
+      JNIEnv* jni,
+      std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams) {
+    jobjectArray java_streams =
+        jni->NewObjectArray(streams.size(), *j_media_stream_class_, nullptr);
+    int i = 0;
+    for (rtc::scoped_refptr<MediaStreamInterface> stream : streams) {
+      NativeToJavaStreamsMap::iterator it = remote_streams_.find(stream);
+      if (it != remote_streams_.end()) {
+        jobject j_stream = it->second;
+        CHECK_EXCEPTION(jni) << "error during NewObject";

[Taylor Brandstetter, 2016/11/17 23:02:53]

I think this CHECK_EXCEPTION needs to be right after "NewObjectArray". And the
message should be "error during NewObjectArray".

[Zhi Huang, 2016/11/18 02:22:10]

Done.

+        jni->SetObjectArrayElement(java_streams, i++, j_stream);
+      }

[Taylor Brandstetter, 2016/11/17 23:02:53]

There should be an "else" with an RTC_DCHECK.

[Zhi Huang, 2016/11/18 02:22:10]

What about always creating new stream if we cannot find one in the map?

+    }
+    return java_streams;
+  }
+
   JNIEnv* jni() {
     return AttachCurrentThreadIfNeeded();
   }
@@ -437,6 +473,8 @@ class PCOJava : public PeerConnectionObserver {
   const jmethodID j_video_track_ctor_;
   const ScopedGlobalRef<jclass> j_data_channel_class_;
   const jmethodID j_data_channel_ctor_;
+  const ScopedGlobalRef<jclass> j_rtp_receiver_class_;
+  const jmethodID j_rtp_receiver_ctor_;
   // C++ -> Java remote streams. The stored jobects are global refs and must be
   // manually deleted upon removal. Use DisposeRemoteStream().
   NativeToJavaStreamsMap remote_streams_;