播放其他声音时尝试限制其他声音

Question

如果正在播放其他声音，我正在尝试发出声音。但是，我编写的代码无法执行。

 public class Transportation extends AppCompatActivity {

        private MediaPlayer sound,sound1;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.transportation);

            sound = MediaPlayer.create(this,R.raw.vatunabus);
            final ImageView imageView= (ImageView)findViewById(R.id.vatunabussound);
            imageView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    if(sound1.isPlaying()){
                        sound.stop();
                        sound.release();
                    }
                    else if(sound.isPlaying()){
                        sound.pause();

                    }
                    else {
                        sound.start();

                    }
                }
            });            


            sound1 = MediaPlayer.create(this,R.raw.varowlsanabus);
            final ImageView imageView1 = (ImageView)findViewById(R.id.firstbussound);
            imageView1.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    if(sound.isPlaying()){
                        sound1.stop();
                        sound1.release();
                    }
                    else if(sound1.isPlaying()){
                        sound1.pause();

                    }
                    else {
                        sound1.start();

                    }

                }
            });         

        }

    }