android - 选择要用 MediaPlayer 播放的音乐文件

Question

我是 Android 编程的新手，现在我的应用程序出现问题。我打算编写一个具有以下功能的 MediaPlayer 应用程序:使用 intent 从存储中选择一个文件，然后开始播放该文件。我使用“MediaPlayer.create(context, uri)”方法，但目前出现错误

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //openFile();
    Button openFile = (Button) this.findViewById(R.id.ButtonOpen);
    openFile.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            Intent chooseFile;
            Intent intent;
            chooseFile = new Intent(Intent.ACTION_GET_CONTENT);
            chooseFile.setType("file/*");
            intent = Intent.createChooser(chooseFile, "Choose a file");
            startActivityForResult(intent, ACTIVITY_CHOOSE_FILE);

            Uri uri = intent.getData();
            initViews(uri);
        }
    }); 

}

private void initViews(Uri uri) {
    mButtonPlayStop = (Button) findViewById(R.id.ButtonPlayStop);
    mButtonPlayStop.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            buttonClick();
        }
    });

    mMediaPlayer = MediaPlayer.create(this, uri);
}


private void starPlayProgressUpdater() {
    mSeekBar.setProgress(mMediaPlayer.getCurrentPosition());

    if (mMediaPlayer.isPlaying()) {
        Runnable notification = new Runnable() {

            @Override
            public void run() {
                starPlayProgressUpdater();
            }
        };
        mHandler.postDelayed(notification, 1000);
    } else {
        mMediaPlayer.pause();
        mButtonPlayStop.setText(getString(R.string.play_str));
        mSeekBar.setProgress(0);
    }
}

private void buttonClick() {
    if (mButtonPlayStop.getText() == getString(R.string.play_str)) {
        mButtonPlayStop.setText(getString(R.string.pause_str));
        try {
            mMediaPlayer.start();
            starPlayProgressUpdater();              
        } catch (IllegalStateException e) {
            mMediaPlayer.pause();
        }
    } else {
        mButtonPlayStop.setText(getString(R.string.play_str));
        mMediaPlayer.pause();
    }
}

它在“mMediaPlayer = MediaPlayer.create(this, uri);”中抛出 NullPointerException。 uri 有问题。谁能指导我一下？

---

感谢 Ilango j，我修改了我的代码，现在我可以选择并播放音乐文件了。但我的期望是选择文件，然后仅在单击播放/暂停按钮(带进度条)后播放，但我的 buttonClick 出现了新的 NullPointerException

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mContext = (Context) getApplicationContext();

    Button openFile = (Button) this.findViewById(R.id.ButtonOpen);
    openFile.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {       
            initView();
        }
    }); 

}

private void initView() {
    mButtonPlayStop = (Button) findViewById(R.id.ButtonPlayStop);
    mButtonPlayStop.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            buttonClick();
        }
    });

    Intent intent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI);
    startActivityForResult(intent, 10);

}
    @Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == RESULT_OK && requestCode == 10) {
        Uri uri = data.getData();

        mMediaPlayer = MediaPlayer.create(mContext, uri);

        mSeekBar = (SeekBar) findViewById(R.id.SeekBar01);
        mSeekBar.setMax(mMediaPlayer.getDuration());
        mSeekBar.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                seekChange(v);
                return false;
            }
        });         
    }
}   

private void starPlayProgressUpdater() {
    mSeekBar.setProgress(mMediaPlayer.getCurrentPosition());

    if (mMediaPlayer.isPlaying()) {
        Runnable notification = new Runnable() {

            @Override
            public void run() {
                starPlayProgressUpdater();
            }
        };
        mHandler.postDelayed(notification, 1000);
    } else {
        mMediaPlayer.pause();
        mButtonPlayStop.setText(getString(R.string.play_str));
        mSeekBar.setProgress(0);
    }
}

private void seekChange(View v) {
    if (mMediaPlayer.isPlaying()) {
        SeekBar sb = (SeekBar) v;
        mMediaPlayer.seekTo(sb.getProgress());
    }
}

private void buttonClick() {
    if (mButtonPlayStop.getText().equals(getString(R.string.play_str))) {
        mButtonPlayStop.setText(getString(R.string.pause_str));
        try {
            mMediaPlayer.start();
            starPlayProgressUpdater();              
        } catch (IllegalStateException e) {
            mMediaPlayer.pause();
        }
    } else {
        mButtonPlayStop.setText(getString(R.string.play_str));
        mMediaPlayer.pause();
    }
}

你能给个建议吗？

Answer 1

首先从 sd 卡启动 pic 媒体文件的 Activity 。替换以下代码

Button openFile = (Button) this.findViewById(R.id.ButtonOpen);
    openFile.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
           Intent intent = new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI);
                startActivityForResult(intent, 10);
        }
    }); 

然后在onActivityResult

中添加如下代码

     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {

          if(resultCode == RESULT_OK && requestCode == 10){
                Uri uriSound=data.getData();
                play(this, uriSound); 
          }
      }

然后调用下面的方法来创建媒体播放器并播放选定的音频文件。

   private void play(Context context, Uri uri) {

        try {
            MediaPlayer mp = new MediaPlayer();
            mp.setDataSource(context, uri);         
            mp.start();
          } catch (IllegalArgumentException e) {
          // TODO Auto-generated catch block
             e.printStackTrace();
          } catch (SecurityException e) {
          // TODO Auto-generated catch block
             e.printStackTrace();
          } catch (IllegalStateException e) {
          // TODO Auto-generated catch block
             e.printStackTrace();
          } catch (IOException e) {
          // TODO Auto-generated catch block
             e.printStackTrace();
          }
    }