无法使用Mediaplayer Android播放mp3

Question

I pressed the button to play abc.mp3 file and "unfortunately, the app has stopped".

Java

public class MainActivity extends AppCompatActivity{
  MediaPlayer background_music;


protected void onCreate(Bundle savedInstanceState) {
  background_music.create(this,R.raw.abc);
}

public void playMusic(View view) {
  background_music.start();
}

}

xml

    <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="New Button"
    android:id="@+id/button"
    ...
    android:onClick="playMusic" />

It just basically plays music and I don't know why the error comes up. Please help me.

Answer 1

It is NullPointerException since background_music is NULL & you try to call start() on a null object reference.

background_music.create(this,R.raw.abc);

The above code returns a MediaPlayer object but it is not saved to background_music object. So you should initialize it to

background_music = background_music.create(this,R.raw.abc);

OR

background_music = MediaPlayer.create(this,R.raw.abc); //since create() is static

Answer 2

activity_main.xml -

<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" >  

    <TextView  
        android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignParentTop="true"  
        android:layout_marginTop="30dp"  
        android:text="Audio Controller" />  

    <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>  

MainActivity-

public class MainActivity extends Activity {  
    Button start,pause,stop;  
    @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  
        final MediaPlayer mp=new MediaPlayer();  
        try{  
                //you can change the path, here path is external directory(e.g. sdcard) /Music/maine.mp3  
        mp.setDataSource(Environment.getExternalStorageDirectory().getPath()+"/Music/maine.mp3");  

        mp.prepare();  
        }catch(Exception e){e.printStackTrace();}  

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

Use this code.