我在Android上构建了一个简单的音乐播放器。每首歌的视图都包含一个SeekBar,实现如下:

public class Song extends Activity implements OnClickListener,Runnable {
    private SeekBar progress;
    private MediaPlayer mp;

    // ...

    private ServiceConnection onService = new ServiceConnection() {
          public void onServiceConnected(ComponentName className,
            IBinder rawBinder) {
              appService = ((MPService.LocalBinder)rawBinder).getService(); // service that handles the MediaPlayer
              progress.setVisibility(SeekBar.VISIBLE);
              progress.setProgress(0);
              mp = appService.getMP();
              appService.playSong(title);
              progress.setMax(mp.getDuration());
              new Thread(Song.this).start();
          }
          public void onServiceDisconnected(ComponentName classname) {
              appService = null;
          }
    };

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.song);

        // ...

        progress = (SeekBar) findViewById(R.id.progress);

        // ...
    }

    public void run() {
    int pos = 0;
    int total = mp.getDuration();
    while (mp != null && pos<total) {
        try {
            Thread.sleep(1000);
            pos = appService.getSongPosition();
        } catch (InterruptedException e) {
            return;
        } catch (Exception e) {
            return;
        }
        progress.setProgress(pos);
    }
}

这很好。现在我想要一个计时器计算秒/分钟的歌曲的进展。所以我把一个TextView在布局,得到它与findViewById()在onCreate(),并把这个在run()后的progress.setProgress(pos):

String time = String.format("%d:%d",
            TimeUnit.MILLISECONDS.toMinutes(pos),
            TimeUnit.MILLISECONDS.toSeconds(pos),
            TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(
                    pos))
            );
currentTime.setText(time);  // currentTime = (TextView) findViewById(R.id.current_time);

但最后一句给了我一个例外:

android.view。只有创建视图层次结构的原始线程才能触及它的视图。

然而,我在这里所做的事情基本上与我在SeekBar中所做的事情相同——在onCreate中创建视图,然后在run()中触摸它——它没有给我这个抱怨。


当前回答

我通过将runOnUiThread(new Runnable(){..在run ():

thread = new Thread(){
        @Override
        public void run() {
            try {
                synchronized (this) {
                    wait(5000);

                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            dbloadingInfo.setVisibility(View.VISIBLE);
                            bar.setVisibility(View.INVISIBLE);
                            loadingText.setVisibility(View.INVISIBLE);
                        }
                    });

                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Intent mainActivity = new Intent(getApplicationContext(),MainActivity.class);
            startActivity(mainActivity);
        };
    };  
    thread.start();

其他回答

对于任何使用fragment的人:

(context as Activity).runOnUiThread {
    //TODO
}

如果你只是想从你的非UI线程中无效(调用重绘/重画函数),使用postInvalidate()

myView.postInvalidate();

这将在ui线程上发布一个无效请求。

有关更多信息:what-does-postinvalidate-do

我使用Handler与loop . getmainlooper()。这对我来说很有效。

    Handler handler = new Handler(Looper.getMainLooper()) {
        @Override
        public void handleMessage(Message msg) {
              // Any UI task, example
              textView.setText("your text");
        }
    };
    handler.sendEmptyMessage(1);

如果你在一个片段中,那么你还需要获取活动对象,因为runOnUIThread是活动上的一个方法。

Kotlin中的一个例子,有一些周围的上下文,让它更清楚-这个例子是从一个相机片段导航到一个画廊片段:

// Setup image capture listener which is triggered after photo has been taken
imageCapture.takePicture(
       outputOptions, cameraExecutor, object : ImageCapture.OnImageSavedCallback {

           override fun onError(exc: ImageCaptureException) {
           Log.e(TAG, "Photo capture failed: ${exc.message}", exc)
        }

        override fun onImageSaved(output: ImageCapture.OutputFileResults) {
                        val savedUri = output.savedUri ?: Uri.fromFile(photoFile)
                        Log.d(TAG, "Photo capture succeeded: $savedUri")
               
             //Do whatever work you do when image is saved         
             
             //Now ask navigator to move to new tab - as this
             //updates UI do on the UI thread           
             activity?.runOnUiThread( {
                 Navigation.findNavController(
                        requireActivity(), R.id.fragment_container
                 ).navigate(CameraFragmentDirections
                        .actionCameraToGallery(outputDirectory.absolutePath))
              })

解决:把这个方法放在doInBackround类…然后传递信息

public void setProgressText(final String progressText){
        Handler handler = new Handler(Looper.getMainLooper()) {
            @Override
            public void handleMessage(Message msg) {
                // Any UI task, example
                progressDialog.setMessage(progressText);
            }
        };
        handler.sendEmptyMessage(1);

    }