Android 音乐播放器 - 一次一个 PlayerActivity

Question

我正在编写一个音乐播放器，我有 2 个活动：

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

   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;
       }
   }
   

2. 第二个（PlayerActivity）有一个歌曲的字符串路径的ArrayList，并使用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;
       }
   }
   

它运行良好，但是当我返回到第一个活动 (MainActivity) 然后我点击另一个项目（或同一个项目）时，它会创建另一个 PlayerActivity，因此应用程序同时播放 2 首歌曲.

我怎样才能实现它以便它只创建一个 PlayerActivity？

Answer 1

检查清单中 Activity 的启动模式。 https://developer.android.com/guide/topics/manifest/activity-element.html#lmode

Answer 2

解决了！我试图通过 Intent 传递在 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：

1. 创建一个扩展 Application 的类并在那里实例化 MediaPlayer，这样我就有了一个全局 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;
       }
   }
   

2. 在 AndroidManifest.xml 中将 MyApp 设置为我的应用程序的名称：

   <application
   android:name="NicoPlayer"
   ...>
       ...
   </application>
   

3. 在 PlayerActivity 中创建一个 MediaPlayer 实例并调用 getMediaPlayer() 将全局 MediaPlayer 实例分配给它，所有这些都在 onCreate() 方法中。完成此操作并且 mediaPlayer 正在播放后，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();
   }