java - 阻止用户调用父函数

Question

更新(24/10/19):我稍微修改了问题的语言。投反对票的人，如果仍然不清楚，请通过评论公开告诉我，这样我就可以进一步完善它(我只是看到最后的投票说不清楚，既没有模组名称也没有原因)。请注意，英语不是我的母语，我真的需要这方面的帮助。

<小时/>

所以我猜这与 java 基础知识和 OOP 更相关，但我已经看到了常见 Android 类遵循的一些模式。 Google 经常弃用旧功能，转而支持更好的功能，我正在考虑对我的自定义 View 做类似的事情。

我想在 android 中构建一个视频播放器，它应该很容易创建，并且应该返回多个事件的回调。为此，我希望用户使用我的功能而不是内置视频 View 的功能。因此，我正在应用几种方法来阻止用户使用这些内置函数:

• 我使用 @Deprecated 表示法来显示带有 Strike 的函数名称，例如 getVolume()
• 我已经覆盖了那些我不希望用户使用的函数，并用如下错误替换了它们的实现:

@Override @deprecated
public void getWidth(){
    throw new UnsupportedOperationException("useMyVideoPlayer#getVideoWidth()");
}

• 我自己在 init() 或其各自的替代方案中实现这些函数。这是代码(检查代码行上的注释:super.setOnErrorListener(errorListener);)

public class MyVideoPlayer extends VideoView {
    public static final String TAG = "MyVP>>";

    private MyPlayerCurrentPlaybackState currentPlaybackState;
    private MediaController mediaController;

    @Nullable
    private MyVideoPlayerListener playerListener;

    public MyVideoPlayer(Context context) {
        super(context);
        init();
    }
    public MyVideoPlayer(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }
    public MyVideoPlayer(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
    public MyVideoPlayer(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    public void init() {
        currentPlaybackState = MyPlayerCurrentPlaybackState.STOPPED;
        mediaController = new MediaController(this.getContext());
        mediaController.setAnchorView(this);

        MediaPlayer.OnCompletionListener onCompletionListener = new MediaPlayer.OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                Log.e(TAG, "internalListener:onCompletion: called");
                mp.reset();
                mp.setDisplay(MyVideoPlayer.this.getHolder());
                currentPlaybackState = MyPlayerCurrentPlaybackState.STOPPED;
                if (playerListener != null) {
                    playerListener.onCompleted(mp);
                } else {
                    Log.e(TAG, "onCompletionListener:onCompletion: playerListener is null");
                }

            }
        };
        super.setOnCompletionListener(onCompletionListener);

        MediaPlayer.OnErrorListener errorListener = new MediaPlayer.OnErrorListener() {
            @Override
            public boolean onError(MediaPlayer mp, int what, int extra) {
                currentPlaybackState = MyPlayerCurrentPlaybackState.STOPPED;
                if (playerListener != null) {
                    playerListener.onError(what, extra);
                } else {
                    Log.e(TAG, "errorListener:onError: playerListener is null");

                }
                return true;// indicates we handled error

            }
        };
        super.setOnErrorListener(errorListener);// <---setting error listener *inside* the view only and making setOnErrorListener(...) deprecated so that user won't use it

        MediaPlayer.OnPreparedListener preparedListener = new MediaPlayer.OnPreparedListener() {
            @Override
            public void onPrepared(MediaPlayer mp) {
                //play(); // or should we call mp.start?
                if (playerListener != null) {
                    playerListener.onPlayerPrepared(MyVideoPlayer.this);
                } else {
                    Log.e(TAG, "preparedListener:onPrepared: player listener is null");
                }
            }
        };
        super.setOnPreparedListener(preparedListener);




    }

    @Nullable
    public MyVideoPlayerListener getMyPlayerListener() {
        return playerListener;
    }

    public void setMyPlayerListener(@NonNull MyVideoPlayerListener playerListener) {
        this.playerListener = playerListener;
    }

    //---------following methods throw exception, do not use-----vvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    @Override @Deprecated
    public void setOnCompletionListener(@Nullable MediaPlayer.OnCompletionListener implementorsListener) {
        //update: user is now not adding the on completion listener at all. he/she will only use our methods now.
        throw new UnsupportedOperationException("Use MyVideoPlayer#setMyPlayerListener(...) ");
    }

    @Override @Deprecated
    public void setOnErrorListener(MediaPlayer.OnErrorListener implementorsListener) {
        //update: user is now not adding the on completion listener at all. he/she will only use our methods now.
        throw new UnsupportedOperationException("Use MyVideoPlayer#setMyPlayerListener(...) ");
    }

    @Override @Deprecated
    public int getDuration() {
        throw new UnsupportedOperationException("Use MyVideoPlayer#gettotalDuration(...) ");
    }

    @Deprecated
    public void start() {
        // did because it doesn't look cool
        throw new UnsupportedOperationException("Use MyVideoPlayer#play() ");
    }

    @Override @Deprecated
    public void stopPlayback() {
        // did because it doesn't look cool
        throw new UnsupportedOperationException("Use MyVideoPlayer#stop() ");
    }

    //----------------------------------------------------------------------------------------------
    @Override @Deprecated
    public void setOnPreparedListener(MediaPlayer.OnPreparedListener implementorsListener) {
        throw new UnsupportedOperationException("use MyVideoPlayer#onPlayerPrepared()");
    }



    public void play() {
        super.start();
        if (playerListener != null) {
            playerListener.onPlay();
        } else {
            Log.e(TAG, "play: player listener is null");
        }
        currentPlaybackState = MyPlayerCurrentPlaybackState.PLAYING;
    }

    @Override
    public void pause() {
        // didn't throwed any exception because its already cool

        super.pause();

        currentPlaybackState = MyPlayerCurrentPlaybackState.PAUSED;

        if (playerListener != null) {
            playerListener.onPause();
        } else {
            Log.e(TAG, "play: player listener is null");
        }

    }


    @Override
    public void resume() {
        // didn't throwed any exception because its already cool

        super.start();
        if (playerListener != null) {
            playerListener.onResume();
        } else {
            Log.e(TAG, "play: player listener is null");
        }
        currentPlaybackState = MyPlayerCurrentPlaybackState.PLAYING;

    }

    public void stop() {
        if (currentPlaybackState != MyPlayerCurrentPlaybackState.STOPPED) {
            super.stopPlayback();
            if (playerListener != null) {
                playerListener.onStop();
            } else {
                Log.e(TAG, "play: player listener is null");
            }
            currentPlaybackState = MyPlayerCurrentPlaybackState.STOPPED;
        }
    }


    public int gettotalDuration() {
        return currentPlaybackState ==
                MyPlayerCurrentPlaybackState.STOPPED ? 0 : super.getDuration();
    }

    //returns current video volume in range 0-100
    public int getVolume() {
        // Get the system's audio service and get media volume from it.
        AudioManager audioManager =
                (AudioManager) getContext().getSystemService(Context.AUDIO_SERVICE);
        if (audioManager != null) {
            double volume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
            double max = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
            if (max <= 0) {
                return 0;
            }
            // Return a range from 0-100.
            return (int) ((volume / max) * 100.0f);
        }
        return 0;
    }


    public enum MyPlayerCurrentPlaybackState {
        STOPPED, PAUSED, PLAYING
    }


    public interface MyVideoPlayerListener {
        void onPlay();

        void onPause();

        void onResume();

        void onCompleted(MediaPlayer mp);

        void onError( int what, int extra);

        void onPlayerPrepared(MyVideoPlayer myVideoPlayer);

        void onStop();
    }



    /* must implement features
    public interface VideoPlayer {

    void play();
    void pause();
    void resume();
    int getCurrentPosition();
    void seekTo(int videoPosition);
    int getDuration();
    int getVolume();
    void stopPlayback();
    void disablePlaybackControls();
    void enablePlaybackControls();
    void setVideoPath(String videoUrl);
    void addPlayerCallback(PlayerCallback callback);
    void removePlayerCallback(PlayerCallback callback);

}
    *
    * */


}

我希望上面的示例显示了我的 Intent :我希望用户不使用内置方法，例如 start() 、 setOnErrorListener(...) 等，但库要么自己处理这些函数(并向用户提供回调)，要么定义了一些我希望用户使用的其他函数，而不是内置函数(例如我希望用户调用自定义 View 的 play() 函数，而不是通过 inheritance. 来自父级的已存在的 start() 函数)

但是当我通过这些行调用代码时:

        MyVideoPlayer mvp = findViewById(R.id.mvp_main);
        mvp.setVideoURI(Uri.parse(MyTags.CONTENT_URL));
        mvp.setMyPlayerListener(new MyVideoPlayer.MyVideoPlayerListener() {
            @Override
            public void onPlay() {
                Log.e(TAG, "onPlay: Video is now playing" );
            }

            @Override
            public void onPause() {
                Log.e(TAG, "onPause: Video Paused" );
            }

            @Override
            public void onResume() {
                Log.e(TAG, "onResume: video resumed" );

            }

            @Override
            public void onCompleted(MediaPlayer mp) {
                Log.e(TAG, "onCompleted: video playback completed" );

            }

            @Override
            public void onError(int what, int extra) {
                Log.e(TAG, "onError: error happenned: what:"+what+",extra:"+extra );
            }

            @Override
            public void onPlayerPrepared(MyVideoPlayer myVideoPlayer) {
                Log.e(TAG, "onPlayerPrepared: video is prepared,plau video" );
                myVideoPlayer.play();
            }

            @Override
            public void onStop() {
                Log.e(TAG, "onStop: media playback stopped" );

            }
        });

即，当用户在他们的应用程序中使用我的库时，在调用这些库定义的函数(例如 mvp.play() )时会给出异常 java.lang.UnsupportedOperationException: Use MyVideoPlayer #play() ，表示正在调用我重写的 start() 函数，而不是 super.start() 。为什么？另外，我是否正确使用了 @Deprecated 注释(这只是为了显示删除线警告)或者该注释是否也进行了一些不需要的更改？

Answer 1

您可以应用代理/装饰模式:

编写您自己的 Videoplayer 来实现和扩展原始 Vidoeview 实现的那些类。这是一个伪代码，可以给您一个想法:

     //extends and implements the same interface and parent as the VideoView did, o that they will have the same methods to work properly.
      public  class MyVideoViewer extends SurfaceView implements 
          MediaController.MediaPlayerControl{
      //private modifier to prevent others from directly calling the system's player
      private VideoView view;

      //you can just delete start method, so users using your player cannot even see this method.
       /**void  start(){

      }*/

     public void init(){
       // do your things. can necessary method from videoplayer
       view.setOnCompletionListener(listener) etc.

    }
     public void play()
     {
        view.start();
    }
    //indirectly call all necessary methods to make sure the system's player work properly. 
   @override
    public void draw(arg1,arg2){
        view.draw(arg1,arg2);
     }
}

通过这样做，您的播放器仅公开您希望其公开的方法，将所有不必要的方法隐藏在用户后面。它仍然可以正常工作，因为在下面，有一个适合您的播放器的正确系统Videoview。