媒体控制器加载声音文件时,进度对话框不显示

我正在使用媒体控制器和媒体播放器从服务器加载声音文件。我想在加载声音文件时显示进度对话框。问题实际上是进度车显示,但不是我一按下按钮就显示,而是在媒体控制器显示之前立即显示和隐藏。媒体控制器工作正常。

 ImageButton soundLoader = (ImageButton)getActivity().findViewById(R.id.lifeObjectSound);
             soundLoader.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View arg0) {
                    progress = ProgressDialog.show(getActivity(), "dialog title",
                            "dialog message", true);

                     mediaPlayer = new MediaPlayer();
                        mediaPlayer.setOnPreparedListener(currentFragment);

                        mediaController = new MediaController(getActivity());


                          try {
                            mediaPlayer.setDataSource("https://dl.dropboxusercontent.com/u/108022472/5041046.mp3");
                             mediaPlayer.prepare();
                        } catch (IllegalArgumentException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        } catch (SecurityException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        } catch (IllegalStateException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }

                          mediaPlayer.start();

                }
            });

我正在停止进度对话框,如下所示:

@Override
        public void onPrepared(MediaPlayer mp) {
            Log.d("media status", "onPrepared");
            mediaController.setMediaPlayer(this);
            mediaController.setAnchorView(getView());


            handler.post(new Runnable() {
              public void run() {
                mediaController.setEnabled(true);
                mediaController.show(0);
                progress.dismiss();
              }
            });

        }