Android TV Input Framework(TIF)--3 显示Tv Input内容

上一篇文章我们分析了TvInputManagerService如何构建Tv Input list，这篇文章主要分析如何切换到Tv Input，并显示其内容。App一般通过TvView来跟TvInputService建立联系，通过调用TvView的方法来选择Tv Input，显示内容。我们看一下 Android开发文档对TvView的描述：

TvView类概述：
显示TV内容。TvView类为应用程序提供了一个高级接口，以显示实现TvInputService的各种TV信号源的节目。（注意系统上可用的TV Inputs列表可以通过调用TvInputManager.getTvInputList()来获取。
一旦应用程序提供了特定TV通道的URL给tune(String, Uri)方法，它负责下层的服务绑定（和解除绑定如果当前的TvView已经绑定到一个服务)并且根据需要自动的分配或者释放资源。除了一些控制内容如何呈现的基本方法，它也提供了一个给已经连接的TvInputService分发输入事件的办法，以允许为Tv Input客制化按键动作。

---

Tv Input的选择和显示是通过TvView的tune方法来做的，我们看一下tune的实现:

    /**
     * Tunes to a given channel.
     *
     * @param inputId The ID of TV input which will play the given channel.
     * @param channelUri The URI of a channel.
     * @param params Extra parameters which might be handled with the tune event.
     * @hide
     */
    @SystemApi
    public void tune(String inputId, Uri channelUri, Bundle params) {
        ...
        if (mSessionCallback != null && mSessionCallback.mInputId.equals(inputId)) {
            if (mSession != null) {
                mSession.tune(channelUri, params);
            } else {
                // Session is not created yet. Replace the channel which will be set once the
                // session is made.
                mSessionCallback.mChannelUri = channelUri;
                mSessionCallback.mTuneParams = params;
            }
        } else {
            resetInternal();
            // When createSession() is called multiple times before the callback is called,
            // only the callback of the last createSession() call will be actually called back.
            // The previous callbacks will be ignored. For the logic, mSessionCallback
            // is newly assigned for every createSession request and compared with
            // MySessionCreateCallback.this.
            mSessionCallback = new MySessionCallback(inputId, channelUri, params);
            if (mTvInputManager != null) {
                mTvInputManager.createSession(inputId, mSessionCallback, mHandler);
            }
        }
    }

tune方法有三个参数，我们只关注第一个参数inputId，每个Tv Input都有一个唯一的inputId和TvInputInfo实例，inputId由TvInputInfo.getId()获取。第一次调用tune的时候，mSessionCallback为null，所以首先执行mSessionCallback = new MySessionCallback(inputId, channelUri, params)创建一个SessionCallback实例，然后通过mTvInputManager.createSession(inputId, mSessionCallback, mHandler)来跟TvInputService之间创建一个会话，当会话创建成功以后，mSessionCallback被回调回来，createSession的具体细节我们忽略掉，最终会调用到TvInputService的createSession，

          public void createSession(InputChannel channel, ITvInputSessionCallback cb,
                    String inputId) {
                if (channel == null) {
                    Log.w(TAG, "Creating session without input channel");
                }
                if (cb == null) {
                    return;
                }
                SomeArgs args = SomeArgs.obtain();
                args.arg1 = channel;
                args.arg2 = cb;
                args.arg3 = inputId;
                mServiceHandler.obtainMessage(ServiceHandler.DO_CREATE_SESSION, args).sendToTarget();
            }

接着ServiceHandler.handleMessage

    public final void handleMessage(Message msg) {
            switch (msg.what) {
                case DO_CREATE_SESSION: {
                    SomeArgs args = (SomeArgs) msg.obj;
                    InputChannel channel = (InputChannel) args.arg1;
                    ITvInputSessionCallback cb = (ITvInputSessionCallback) args.arg2;
                    String inputId = (String) args.arg3;
                    args.recycle();
                    Session sessionImpl = onCreateSession(inputId);
                    ...
  else {
                        SomeArgs someArgs = SomeArgs.obtain();
                        someArgs.arg1 = sessionImpl;
                        someArgs.arg2 = stub;
                        someArgs.arg3 = cb;
                        someArgs.arg4 = null;
                        mServiceHandler.obtainMessage(ServiceHandler.DO_NOTIFY_SESSION_CREATED,
                                someArgs).sendToTarget();
                    }
                    return;
                }
                case DO_NOTIFY_SESSION_CREATED: {
                    SomeArgs args = (SomeArgs) msg.obj;
                    Session sessionImpl = (Session) args.arg1;
                    ITvInputSession stub = (ITvInputSession) args.arg2;
                    ITvInputSessionCallback cb = (ITvInputSessionCallback) args.arg3;
                    IBinder hardwareSessionToken = (IBinder) args.arg4;
                    try {
                        cb.onSessionCreated(stub, hardwareSessionToken);
                    } catch (RemoteException e) {
                        Log.e(TAG, "error in onSessionCreated");
                    }
                    if (sessionImpl != null) {
                        sessionImpl.initialize(cb);
                    }
                    args.recycle();
                    return