java - 如何停止在 UIThread 上运行的 Runnable

Question

当 MediaPlayer 正在播放时，我在 UIThread 上有一个 Runnable 更新 SeekBar。然而，当我切换到另一个 Activity 时，我的应用程序因异常而崩溃，导致 Runnable 即使在 MediaPlayer 被销毁后也会永远保持运行。

这是我的代码:

public class Guide extends AppCompatActivity implements MediaPlayer.OnPreparedListener {

    Button back;
    private MediaPlayer m_audio_player;
    private Handler m_handler_seek_bar = new Handler();
    private SeekBar m_seek_bar;
    private Runnable m_seek_bar_runnable;

    private void set_up_audio(){
        m_audio_player = MediaPlayer.create(this, g_audio[NativeLib.get_active_landmark()] );
        m_audio_player.setOnPreparedListener(this);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_guide);
        implement_back_button();
        set_up_audio();
    }

    @Override
    protected void onStart() {
        super.onStart();
        set_up_seek_bar();
    }

    private void set_up_seek_bar() {
        m_seek_bar = (SeekBar) findViewById(R.id.seek_bar);
        m_seek_bar.setMax(m_audio_player.getDuration());
        m_seek_bar_runnable = new Runnable() {
            @Override
            public void run() {
                if(m_audio_player != null ){
                    m_seek_bar.setProgress(m_audio_player.getCurrentPosition());
                }
                m_handler_seek_bar.postDelayed(this, 1000);
            }
        };
        // update Seekbar on UI thread
        Guide.this.runOnUiThread(m_seek_bar_runnable);
        m_seek_bar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onStopTrackingTouch(SeekBar seekBar) { }
            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {}
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                if(m_audio_player != null && fromUser){
                    m_audio_player.seekTo(progress);
                }
            }
        });
    }

    @Override
    protected void onStop() {
        if (debug_mode) Log.d(TAG, "onStop");
        if (m_audio_player.isPlaying()) {
            m_audio_player.stop();
        }
        m_audio_player.release();
        super.onStop();
        findViewById(R.id.activity_guide).removeCallbacks(m_seek_bar_runnable);
    }

    // return button
    private void implement_back_button() {
        final Intent intent = new Intent(/* pointing at some other activity */);
        back = (Button) findViewById(R.id.back_button);
        back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(intent);
            }
        });
    }
}

Answer 1

你需要使用:

m_handler_seek_bar.removeCallbacks(m_seek_bar_runnable);

从 handler 中移除 runnable

@Override
protected void onStop() {
    if (debug_mode) Log.d(TAG, "onStop");
    if (m_audio_player.isPlaying()) {
        m_audio_player.stop();
    }
    m_audio_player.release();
    m_handler_seek_bar.removeCallbacks(m_seek_bar_runnable);
    super.onStop();
}

或者，您可以覆盖 Activity 的 onPause() 方法:

 @Override
protected void onPause() {
     m_handler_seek_bar.removeCallbacks(m_seek_bar_runnable);
     super.onPause();
}