Question

我正在编写一个音乐播放器，我有两个活动：

第一个（MainActivity）包含歌曲的ListView，我设置了一个OnItemClickListener（在其onCreate（）方法内），它打开一个名为PlayerActivity的新活动，传递已被点击的项目的位置： / p>

public class MainActivity extends AppCompatActivity {
    Intent intent;
    ArrayList<String> artistsTitles;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intent=new Intent(getApplicationContext(), PlayerActivity.class);
        artistsTitles=getArtistTitle();
        ListView mainList=(ListView) findViewById(R.id.mainList);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, android.R.id.text1, artistsTitles);
        mainList.setAdapter(adapter);
        mainList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                intent.putExtra("currentSong", position);
                startActivity(intent);
            }
        });
    }

    private ArrayList<String> getArtistTitle() {
        ContentResolver musicResolve = getContentResolver();
        String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
        String[] projection = { MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.TITLE};
        Uri uri=android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        Cursor cursor = musicResolve.query(uri, projection, selection, null, null);

        ArrayList<String> arrayList=new ArrayList<String>();
        while(cursor.moveToNext())
            arrayList.add(cursor.getString(0)+" - "+cursor.getString(1));

        return arrayList;
    }
}

第二个（PlayerActivity）有一个歌曲字符串路径的ArrayList，并且使用MediaPlayer播放具有项目位置的歌曲并使用它访问ArrayList：

public class PlayerActivity extends AppCompatActivity {
    ArrayList<String> songs;
    MediaPlayer mediaPlayer;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_player);
        songs=new ArrayList<String>();
        songs=getSongs();
        String songPath=songs.get(intent.getIntExtra("songID", 0));
        mediaPlayer=MediaPlayer.create(getApplicationContext(), Uri.parse(songPath));
        try {
            mediaPlayer.reset();
            mediaPlayer.setDataSource(getApplicationContext(), Uri.parse(songPath));
            mediaPlayer.prepare();
            mediaPlayer.start();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private ArrayList<String> getSongs() {
        ContentResolver musicResolve = getContentResolver();

        String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
        String[] projection = {MediaStore.Audio.Media.DATA};
        Uri uri=android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        Cursor cursor = musicResolve.query(uri, projection, selection, null, null);

        ArrayList<String> s = new ArrayList<String>();
        while(cursor.moveToNext())
            s.add(cursor.getString(0));

        return s;
    }
}

它完美无缺，但当我回到第一个活动（MainActivity）然后我点击另一个项目（或相同）时，它会创建另一个PlayerActivity，因此该应用程序同时播放2首歌曲

如何实现它以便它只创建一个PlayerActivity？

Answer 1

检查Manifest中Activity的launchMode。 https://developer.android.com/guide/topics/manifest/activity-element.html#lmode

Answer 2

解决！我试图通过Intent传递一个在MainActivity中创建的MediaPlayer实例，但似乎无法完成。所以，这是我的解决方案：

创建一个扩展Application并在那里实例化MediaPlayer的类，以便我有一个全局的MediaPlayer对象：

import android.app.Application;
import android.media.MediaPlayer;

public class MyApp extends Application {
    MediaPlayer mediaPlayer=null;

    public MediaPlayer getMediaPlayer() {
        return mediaPlayer;
    }

    public void setMediaPlayer(MediaPlayer mediaPlayer) {
        this.mediaPlayer=mediaPlayer;
    }
}

在AndroidManifest.xml中将MyApp设置为我的应用程序的名称：
```
<application
android:name="NicoPlayer"
...>
    ...
</application>
```

在PlayerActivity中创建一个MediaPlayer实例，并将全局MediaPlayer实例分配给它调用getMediaPlayer（），所有这些都在onCreate（）方法中。完成此操作并播放mediaPlayer后，将其分配给调用setMediaPlayer（）的全局MediaPlayer实例：

mediaPlayer=((NicoPlayer)this.getApplication()).getMediaPlayer();
if(mediaPlayer==null)
    mediaPlayer = MediaPlayer.create(getApplicationContext(), Uri.parse(songPath));
((NicoPlayer)this.getApplication()).setMediaPlayer(mediaPlayer);
try {
    mediaPlayer.reset();
    mediaPlayer.setDataSource(getApplicationContext(), Uri.parse(songPath));
    mediaPlayer.prepare();
    mediaPlayer.start();
} catch (IOException e) {
    e.printStackTrace();
}

Android音乐播放器 - 一次一个PlayerActivity

2 个答案: