initializeApplication+snippet+IRtcEngineEventHandler.kt

mRtcEngine = RtcEngine.create(baseContext, APP_ID, object : IRtcEngineEventHandler() {
    override fun onUserJoined(uid: Int, elapsed: Int) {
        // onUserJoined callback is called anytime a new remote user joins the channel
        super.onUserJoined(uid, elapsed)

        // We mute the stream by default so that it doesn't consume unnecessary bandwidth
        mRtcEngine?.muteRemoteVideoStream(uid, true)

        // We are using a lock since uidList is shared and there can be race conditions
        lock.lock()
        try {
            // We are using uidList to keep track of the UIDs of the remote users
            uidList.add(uid)
        } finally {
            lock.unlock()
        }

        // We are using the handler since UI Changes need to be run on the UI Thread
        handler.post {

            // When the number of remote users grows to 4, we switch to the lower stream
            // When this happens, we will now be using a lower resolution and bitrate to save on bandwidth
            if (uidList.size == 4) {
                mRtcEngine?.setRemoteDefaultVideoStreamType(Constants.VIDEO_STREAM_LOW)
                Toast.makeText(
                    applicationContext,
                    "Fallback to Low Video Stream",
                    Toast.LENGTH_LONG
                ).show()
            }

            // We notify our RecyclerView adapter that a new video stream is added
            remoteViewAdapter.notifyItemInserted(uidList.size - 1)
        }
    }

    override fun onUserOffline(uid: Int, reason: Int) {
        // onUserOffline is called whenever a remote user leaves the channel
        super.onUserOffline(uid, reason)

        // We use toRemove to inform the RecyclerView of the index of item we are removing
        val toRemove: Int

        // We are using a lock since uidList is shared and there can be race conditions
        lock.lock()
        try {
            // We are fetching the index of the item we are about to remove and then remove the item
            toRemove = uidList.indexOf(uid)
            uidList.remove(uid)
        } finally {
            lock.unlock()
        }

        // We are using the handler since UI Changes need to be run on the UI Thread
        handler.post {
            // We are using this to remove the remote video from being rendered on the SurfaceView
            mRtcEngine?.setupRemoteVideo(VideoCanvas(null, VideoCanvas.RENDER_MODE_HIDDEN, uid))

            // When the number of remote users shrinks to 3, we switch back to the higher stream
            // When we have <= 3 remote users, the bandwidth savings are no longer necessary
            if (uidList.size == 3) {
                mRtcEngine?.setRemoteDefaultVideoStreamType(Constants.VIDEO_STREAM_HIGH)
                Toast.makeText(
                    applicationContext,
                    "Go back to High Video Stream",
                    Toast.LENGTH_LONG
                ).show()
            }

            // We notify our RecyclerView adapter that the video stream can be removed
            remoteViewAdapter.notifyItemRemoved(toRemove)
        }
    }
})