android强制关闭seekbar

Question

i'm newbie to android programming. i have the following code but i have a problem. when i click on the seekbar without playing the sound it force close. i mean when i click the play button i can click and seek on the seekbar but without clicking the play button clicking on the seekbar will cause force close. what's the problem?!

import android.media.MediaPlayer;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;


    public class MainActivity extends Activity implements Runnable, OnClickListener, OnSeekBarChangeListener{
        private SeekBar seekBar;
        private ImageButton startMedia;
        private ImageButton pauseMedia;
        private MediaPlayer mp;

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);             

            AudioControl();         
        }

        public void AudioControl(){
            seekBar = (SeekBar) findViewById(R.id.seekBar1);
            startMedia = (ImageButton) findViewById(R.id.playbutton);
            pauseMedia = (ImageButton) findViewById(R.id.pausebutton);
            seekBar.setOnSeekBarChangeListener(this);
            startMedia.setOnClickListener(this);
            pauseMedia.setOnClickListener(this); 
        }

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

        public void onClick(View v) {
            if (v.equals(startMedia)) {
                if (mp != null && mp.isPlaying()) return;
                if(seekBar.getProgress() > 0) {
                    mp.start();
                    return;
                }
                mp = MediaPlayer.create(MainActivity.this, R.raw.lone);
                mp.start();                     
                seekBar.setProgress(0);
                seekBar.setMax(mp.getDuration());
                new Thread(this).start();
            }

            if (v.equals(pauseMedia) && mp!=null) {
                mp.pause();
            }       

        }

        public void onStartTrackingTouch(SeekBar seekBar) {
        }

        public void onStopTrackingTouch(SeekBar seekBar) {
        }

        public void onProgressChanged(SeekBar seekBar, int progress,
                boolean fromUser) {
            if(fromUser) mp.seekTo(progress);

        }
    }

and i have another question: i wanna when the user clicks on play button the pause button become visible and when the user clicks on pause button it tuen invisble. what code should i wirte and please tell me where should i put this code.

Answer 1

Every method that manages the UI has to be called on the UI Thread itself:

You can not run

seekBar.setProgress(currentPosition);

on a Thread different frome the UIThread.