Dibujar un círculo al tacto

Estoy tratando de dibujar un círculo donde el usuario toca la pantalla.

public class MainActivity extends Activity implements OnTouchListener { LinearLayout layout; float x=0; float y=0; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_main); layout=(LinearLayout)findViewById(R.id.layout); layout.addView(new CustomView(MainActivity.this)); } public class CustomView extends View { Bitmap mBitmap; Paint paint; public CustomView(Context context) { super(context); mBitmap = Bitmap.createBitmap(400, 800, Bitmap.Config.ARGB_8888); paint=new Paint(); paint.setColor(Color.RED); paint.setStyle(Style.FILL); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.setBitmap(mBitmap); canvas.drawCircle(x, y, 50, paint); Toast.makeText(MainActivity.this, "DDD", 1).show(); } } @Override public boolean onTouch(View v, MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_DOWN) { layout.invalidate(); } return false; }} 

Lo haría de esta manera:

 public class TestActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new DrawingView(this)); } class DrawingView extends SurfaceView { private final SurfaceHolder surfaceHolder; private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); public DrawingView(Context context) { super(context); surfaceHolder = getHolder(); paint.setColor(Color.RED); paint.setStyle(Style.FILL); } @Override public boolean onTouchEvent(MotionEvent event) { if(event.getAction() == MotionEvent.ACTION_DOWN) { if (surfaceHolder.getSurface().isValid()) { Canvas canvas = surfaceHolder.lockCanvas(); canvas.drawColor(Color.BLACK); canvas.drawCircle(event.getX(), event.getY(), 50, paint); surfaceHolder.unlockCanvasAndPost(canvas); } } return false; } } } 

La es su versión con correcciones para que funcione:

 public class MainActivity extends Activity { LinearLayout layout; float x = 0; float y = 0; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); layout=(LinearLayout)findViewById(R.id.layout); layout.addView(new CustomView(MainActivity.this)); } public class CustomView extends View { Bitmap mBitmap; Paint paint; public CustomView(Context context) { super(context); mBitmap = Bitmap.createBitmap(400, 800, Bitmap.Config.ARGB_8888); paint = new Paint(); paint.setColor(Color.RED); paint.setStyle(Style.FILL); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawCircle(x, y, 50, paint); } public boolean onTouchEvent(MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_DOWN) { x = event.getX(); y = event.getY(); invalidate(); } return false; } } }