Android: app crashes after going back and pressing a button

My Android app crashes after a specific set of Buttons are pressed. Basically, the Activity has two Buttons. One plays a sound and the other opens another Activity. But after going back with the back button and pressing the sound Button again, it will crash the app. I'm not sure why since the Button works the first time. I thought I had to reset the MediaPlayer but it still crashes.

My Activity:

public class Tables1 extends Activity {

    MediaPlayer mysound;
    protected boolean active = true;
    protected int splashtime = 17000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.twotime1);
        mysound = MediaPlayer.create(Tables1.this, R.raw.two1);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mysound.stop();
        mysound.reset();
        mysound.release();
        mysound = null;
    }

    public void listen(View view) {

        mysound.setOnCompletionListener(new OnCompletionListener() {
            public void onCompletion(MediaPlayer mysound) {
                mysound.release();
            }

        });
        mysound.start();
    }

    public void Next(View view) {
        if (mysound.isPlaying()) {
            mysound.stop();
            mysound.reset();
        } else {
            Log.d("Exercise", "not working ");
        }

        Intent i = new Intent();
        i.setClassName("com.example", "com.example.twotimes.Exercise1");
        startActivity(i);
    }

    public void back(View view) {
        if (mysound.isPlaying()) {
            mysound.stop();
        }

        Intent i = new Intent();
        i.setClassName("com.example", "com.example.timestableseasy.Menu2");
        startActivity(i);
    }
}

Logcat:

05-30 15:00:35.954: E/AndroidRuntime(31572): FATAL EXCEPTION: main
05-30 15:00:35.954: E/AndroidRuntime(31572): java.lang.IllegalStateException: Could not execute method of the activity
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.view.View$1.onClick(View.java:3814)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.view.View.performClick(View.java:4421)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.view.View$PerformClick.run(View.java:17903)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.os.Handler.handleCallback(Handler.java:730)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.os.Handler.dispatchMessage(Handler.java:92)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.os.Looper.loop(Looper.java:213)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.app.ActivityThread.main(ActivityThread.java:5225)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at java.lang.reflect.Method.invokeNative(Native Method)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at java.lang.reflect.Method.invoke(Method.java:525)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at dalvik.system.NativeStart.main(Native Method)
05-30 15:00:35.954: E/AndroidRuntime(31572): Caused by: java.lang.reflect.InvocationTargetException
05-30 15:00:35.954: E/AndroidRuntime(31572):    at java.lang.reflect.Method.invokeNative(Native Method)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at java.lang.reflect.Method.invoke(Method.java:525)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.view.View$1.onClick(View.java:3809)
05-30 15:00:35.954: E/AndroidRuntime(31572):    ... 11 more
05-30 15:00:35.954: E/AndroidRuntime(31572): Caused by: java.lang.IllegalStateException
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.media.MediaPlayer._start(Native Method)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at android.media.MediaPlayer.start(MediaPlayer.java:1082)
05-30 15:00:35.954: E/AndroidRuntime(31572):    at com.example.twotimes.Tables1.listen(Tables1.java:52)
05-30 15:00:35.954: E/AndroidRuntime(31572):    ... 14 more

Solution

From the Android Documentation:

"IllegalStateException: the internal player engine has not been initialized or has been released."

When you go to your new Activity via an Intent, your previous Activity goes through your onDestroy() method:

mysound.stop();
mysound.reset();
mysound.release();

your mysound is not re-created once the user presses the back button. Try changing your listen() method to this:

public void listen(View view) {
    mysound = MediaPlayer.create(Tables1.this, R.raw.two1);
    mysound.setOnCompletionListener(new OnCompletionListener() {
        public void onCompletion(MediaPlayer mysound) {
            mysound.release();
        }

    });
    mysound.start();
}