java - 获取java.lang.IllegalStateException

Question

在Activity A中，我正在播放一首歌，现在再次移到此处Activity B，以播放另一首歌曲的按钮

现在，我必须在 Activity B上检查是否Activity A's歌曲already playing我必须向用户显示已在 Activity A上播放歌曲的消息，如果用户未在 Activity A上播放歌曲，则用户可以开始在Activity B中播放歌曲

ActivityB.java:-

btnPlay.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub
    if(ActivityA.mPlayer!=null && ActivityA.mPlayer.isPlaying()) // getting exception
    {
    Toast.makeText(Activity.this, "Already playing song on Activity A", Toast.LENGTH_LONG).show();
    }
    else 
    {
    mediaPlayer.start();
    btnPlay.setVisibility(View.GONE);
    btnPause.setVisibility(View.VISIBLE);   
      }
    }
});

现在，当我使用getting进行Exception编码时:就像我已经在Activity playing song中启动A一样，现在移到Activity B了，这里是tapped on play按钮-它的显示 me消息"Already playing song on Activity A"，然后我决定返回 Activity A并暂停了我现在我不在 Activity A中播放歌曲，然后再次移至 Activity B(在这里，当我确实点击Play按钮获取IllegalStateException时)在此行:
if(ActivityA.mPlayer!=null && ActivityA.mPlayer.isPlaying())

**`Logcat:`**

11-01 12:39:38.860: E/AndroidRuntime(7101): FATAL EXCEPTION: main
11-01 12:39:38.860: E/AndroidRuntime(7101): Process: com.example.audio, PID: 7101
11-01 12:39:38.860: E/AndroidRuntime(7101): java.lang.IllegalStateException
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.media.MediaPlayer.isPlaying(Native Method)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at com.example.audio.ActivityB$1.onClick(ActivityB.java:43)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.view.View.performClick(View.java:4438)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.view.View$PerformClick.run(View.java:18431)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.os.Handler.handleCallback(Handler.java:733)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.os.Handler.dispatchMessage(Handler.java:95)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.os.Looper.loop(Looper.java:149)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at android.app.ActivityThread.main(ActivityThread.java:5061)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at java.lang.reflect.Method.invokeNative(Native Method)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at java.lang.reflect.Method.invoke(Method.java:515)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:603)
11-01 12:39:38.860: E/AndroidRuntime(7101):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我认为最好在ActivityA中这样做:

Intent i = new Intent(this, ActivityB.class);
i.putExtra("isPlaying", mPlayer.isPlaying);
startActivity(i);

并在ActivityB's onCreate中:

Bundle data = getIntent().getExtras();

if(data != null)
        {
            isPlayingBefore = data.getParcelable("isPlaying");
        }

在您的onClick上:

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub
    if(isPlayingBefore)
    {
    Toast.makeText(Activity.this, "Already playing song on Activity A", Toast.LENGTH_LONG).show();
    }
    else 
    {
    mediaPlayer.start();
    btnPlay.setVisibility(View.GONE);
    btnPause.setVisibility(View.VISIBLE);   
      }
    }