android开发 onReceiver中调用View为空

Question

切换至下一曲在service中给activity发送广播，在onReceive中改变textView的值，报错textView为空

public class MainActivity extends FragmentActivity implements View.OnClickListener,ViewPager.OnPageChangeListener{
private MyMusicFragment firFragment;
private MusicLibraryFragment secFragment;
private MyFragmentAdapter myFragmentAdapter;
private List lists=new ArrayList<>();
private ViewPager firstViewPager;
private TextView myMusic;
private TextView musicLibrary;
private ImageView shiqu;
private ImageView search;
private ImageView songPicture;
private TextView songName;
private TextView singer;
private ImageView playButton;
private ImageView nextSong;

private View topBar;
private View endPlay;
private LinearLayout.LayoutParams firLayoutParams;
private LinearLayout.LayoutParams secLayoutParams;
private LinearLayout.LayoutParams thiLayoutParams;
private boolean playing=false;
private final int PLAY=0;
private final int PAUSE=-1;
private final int STOP=-2;
private final int CONTINUEPLAY =2;

private static int currentPosition=-1;

private MyBroadcastReceiver broadcastReceiver;
private AutoNextSong autoNextSong;

private NotificationBroadcastReceiver notificationBroadcastReceiver;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    firstViewPager=(ViewPager)findViewById(R.id.firstViewPager);
    myMusic=(TextView)findViewById(R.id.myMusic);
    musicLibrary=(TextView)findViewById(R.id.musicLibrary);
    topBar=findViewById(R.id.topBar);
    endPlay=findViewById(R.id.endPlay);
    shiqu= (ImageView) findViewById(R.id.shiqu);
    search= (ImageView) findViewById(R.id.search);
    songPicture = (ImageView) findViewById(R.id.songPicture);
    **songName= (TextView) findViewById(R.id.songName);**
    singer= (TextView) findViewById(R.id.singer);
    playButton= (ImageView) findViewById(R.id.playButton);
    nextSong= (ImageView) findViewById(R.id.nextSong);

public class AutoNextSong extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
        SongMessage songMessage= (SongMessage) intent.getSerializableExtra("songMessage");
        **songName.setText(songMessage.getSongName());
        singer.setText(songMessage.getSingerName());**
    }
}

}

Answer 1

代码不全，不知道你的broadcastReceiver是在manifest 还是在mainactivity 注册的， 所以不好给出具体的解决方法。
但因为你的receiver 有对UI 进行直接的操作，那么个人理解是最好在MainActivity 的onResume 里注册，并在onPause 里注销。
因为如果没注销，receiver 就一直存在，当service 发送通知，receiver 尝试执行onReceive 并更改textview 时，这个时候MainActivity 可能就不再前台并
可视化了，比如你已经离开MainActivity 去别的Activity, 或程序在后台了。
还有一个方法，但不建议你这么做：
if(songName != null){
songName.setText(songMessage.getSongName())
}