我是初学者，我的Android应用程序遇到了一些麻烦。我的应用程序有2个活动。第一个是PlayerActivity.java，它会列出一个listView中sdcard中的所有歌曲，当我点击一个项目时，PlaysongActivity就会出现。但是当我按下后退按钮时，我会显示歌曲的列表视图再次，但当我再次点击一个项目然后它打开一个新的活动，而旧的仍在播放。现在我有2首歌在同一时间播放。我怎么能解决这个麻烦？这是我的代码。
public class PlayerActivity extends Activity {
String pathToFile = new String("");
private List song = new ArrayList();
ListView listSong;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listSong = (ListView) findViewById(R.id.list);
listAllSong();
}
private void listAllSong() {
String end = ".mp3";
File myMp3Dir = new File("/sdcard/");
final File[] filelist = myMp3Dir.listFiles();
for (File f : filelist) {
if (!f.isDirectory()) {
if (f.getName().toLowerCase().contains(end)) {
song.add(f.getName());
}
}
}
ArrayAdapter adapter = new ArrayAdapter(this,
android.R.layout.simple_list_item_1, song);
listSong.setAdapter(adapter);
listSong.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String path = parent.getItemAtPosition(position).toString();
Intent myIntent = new Intent(getApplicationContext(),
PlaysongActivity.class);
myIntent.putExtra("pathOfSong", path);
startActivity(myIntent);
finish();
}
});
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.player, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.main, container, false);
return rootView;
}
}
}
/和PlaysongActivity /
public class PlaysongActivity extends Activity {
MediaPlayer mp1;
SeekBar seekBar;
Boolean isPaused=false;
Handler mHandler=new Handler();
Boolean isMovingSeekBar=false;
ImageButton button;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_playsong);
TextView tvPlaysong=(TextView) findViewById(R.id.tv);
mp1=new MediaPlayer();
seekBar=(SeekBar) findViewById(R.id.seekBar);
seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
public void onStopTrackingTouch(SeekBar seekBar) {
isMovingSeekBar = false;
}
public void onStartTrackingTouch(SeekBar seekBar) {
isMovingSeekBar = true;
}
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
if (isMovingSeekBar) {
mp1.seekTo(progress);
}
}
});
button=(ImageButton) findViewById(R.id.btnPlay);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (mp1.isPlaying()) {
mp1.pause();
button.setImageResource(android.R.drawable.ic_media_play);
} else if (isPaused) {
mp1.start();
button.setImageResource(android.R.drawable.ic_media_pause);
}
}
});
Intent i=getIntent();
String path=i.getStringExtra("pathOfSong");
tvPlaysong.setText(path);
if(mp1.isPlaying()) mp1.stop();
playSong(path);
}
private void playSong(String path) {
seekBar.setProgress(0);
if(mp1!=null) mp1.stop();
try {
mp1.setDataSource("/sdcard/" + path);
mp1.prepare();
mp1.start();
seekBar.setMax(mp1.getDuration());
updateSeekBar();
isPaused = true;
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (IllegalStateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
button.setImageResource(android.R.drawable.ic_media_pause);
}
private void updateSeekBar() {
mHandler.postDelayed(getTimeTask, 1000);
}
private Runnable getTimeTask=new Runnable() {
public void run() {
long duration=mp1.getDuration();
long currentPosition=mp1.getCurrentPosition();
seekBar.setProgress((int) currentPosition);
mHandler.postDelayed(this, 1000);
}
};
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.playsong, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_playsong,
container, false);
return rootView;
}
}
}