按下主页或后退按钮时如何暂停/停止音乐？

Question

Here is my code. I'm very new to Java and I know that this question is already been posted but still I didn't get the expected outpost so I had to post.

public class MainActivity extends AppCompatActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final MediaPlayer policeSound = MediaPlayer.create(this, R.raw.police);
        Button policeSounds = (Button) this.findViewById(R.id.police);
        policeSounds.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (policeSound.isPlaying()){
                    policeSound.stop();
                }
                else {
                    policeSound.start();
                }
            }
        });
    }
}

I tried adding onBackPressed() code to this but it couldn't detect the 'policeSound' as it was detected in the previous method!

And someone please even teach me how to use @Override annotations!

Answer 1

To detect the 'policeSound' in other methods you need to make it be a field of a class:

private MediaPlayer policeSound;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    policeSound = MediaPlayer.create(this, R.raw.police);
    Button policeSounds = (Button) this.findViewById(R.id.police);
    policeSounds.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (policeSound.isPlaying()) {
                        policeSound.stop();
                    } else {
                        policeSound.start();
                    }
                }
            }
    );
}

Answer 2

In your codes policeSound is a local variable which is be seen only in Oncreate() method,as Oleh Sokolov said, you should declare policeSound as a field of class.

About @Override , you could see this good explanation

and in android studio , when you press ctrl + o in java class file, you can override superclass method, and IDE will add @Override automatically for you.