问Android OnTouch报错

EN

public class MainActivity extends AppCompatActivity{

TouchView touchView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //setContentView(R.layout.activity_main);
    LinearLayout ll = new LinearLayout(this);
    ll.setOrientation(LinearLayout.VERTICAL);
    this.setContentView(ll);

    float x = 500;
    float y = 500;
    float size = 1000;

    touchView = new TouchView(x,y,size,this);
    touchView.setOnTouchListener(this);
    ll.addView(touchView);
}

public boolean onTouch(View view, MotionEvent motionEvent){
    float x = motionEvent.getX();
    float y = motionEvent.getY();

    return  true;
}

public class TouchView extends View {

public float x,y,size;
Paint paint = new Paint();

public TouchView(float xcor, float ycor, float sizenum, Context context) {

    super(context);
    x = xcor;
    y = ycor;
    size = sizenum;
    paint.setAntiAlias(true);

}



@Override
protected void onDraw(Canvas canvas){
    super.onDraw(canvas);

    paint.setColor(Color.BLUE);

    canvas.drawCircle(x, y, size, paint);
}

public TouchView(Context context, AttributeSet attributeSet){

    super(context, attributeSet);

}
}