在Android应用中播放媒体播放器

Question

I am creating a media player with start, pause, stop buttons. Start and stop buttons work fine, the problem is with the pause button.

When no audio files are playing (and also not at all paused any audio), if I click on the pause button, it throws this error message:

Unfortunately App has stopped

What is the problem?

public class activity_12 extends Activity {

    MediaPlayer sound;
    int paused;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_12);
    }
    public void Play(View view) {
        if(sound==null) {
            sound=MediaPlayer.create(this,R.raw.fil);
            sound.start();
        }else if(!sound.isPlaying()) {
            sound.seekTo(paused);
            sound.start();
        }
    }
    public void Pause(View view) {
        sound.pause();
        paused=sound.getCurrentPosition();
    }
    public void Stop(View view) {
        sound.release();
        sound=null;
    }
}

Answer 1

You are facing the problem because you are not declaring the functions properly.Please check this code:

Define your XML like this:

<RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:paddingBottom="@dimen/activity_vertical_margin"  
    android:paddingLeft="@dimen/activity_horizontal_margin"  
    android:paddingRight="@dimen/activity_horizontal_margin"  
    android:paddingTop="@dimen/activity_vertical_margin"  
    tools:context=".MainActivity" >  
  <Button  
        android:id="@+id/button1"  
        style="?android:attr/buttonStyleSmall"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignLeft="@+id/textView1"  
        android:layout_below="@+id/textView1"  
        android:layout_marginTop="48dp"  
        android:text="start" />  

    <Button  
        android:id="@+id/button2"  
        style="?android:attr/buttonStyleSmall"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignTop="@+id/button1"  
        android:layout_toRightOf="@+id/button1"  
        android:text="pause" />  

    <Button  
        android:id="@+id/button3"  
        style="?android:attr/buttonStyleSmall"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignTop="@+id/button2"  
        android:layout_toRightOf="@+id/button2"  
        android:text="stop" />  

</RelativeLayout>

You should define your Activity like this:

import android.media.MediaPlayer;  
import android.os.Bundle;  
import android.os.Environment;  
import android.app.Activity;  
import android.view.Menu;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  

public class MainActivity extends Activity {  
    Button start,pause,stop;  
    MediaPlayer mediaPlayer;  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  

        start=(Button)findViewById(R.id.button1);  
        pause=(Button)findViewById(R.id.button2);  
        stop=(Button)findViewById(R.id.button3);  
        //creating media player  
        mediaPlayer= new MediaPlayer();



        start.setOnClickListener(new OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                mediaPlayer.start();  
            }  
        });  
        pause.setOnClickListener(new OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                mediaPlayer.pause();  
            }  
        });  
        stop.setOnClickListener(new OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                mediaPlayer.stop();  
            }  
        });  
    }  
}  

Answer 2

For reference, MediaPlayer's states are very particular. If you call a state checking function like isPlaying() at the wrong time or in your case .pause() at the wrong time, it will automatically transition to an error state. You need to track the state closely yourself.

Check out the MediaPlayer docs, in particular the State Diagram

And for pause it says in regard to it's relevant states in calling the pause() function:

Successful invoke of this method in a valid state transfers the object to the Paused state. Calling this method in an invalid state transfers the object to the Error state.

An Error state with MediaPlayer invokes a crash.