Drawing with Canvas in Android

Before starting this tutorial please check this site https://developer.mozilla.org/enUS/docs/Web/HTML/Canvas/Drawing_graphics_with_canvas and see that you must use paths (2nd example, beginPath) rather than drawing point by point.

On your Activity

private ArrayList _graphics = new ArrayList();
private Paint mPaint;
@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(new DrawingPanel(this));
  mPaint = new Paint();
  mPaint.setDither(true);
  mPaint.setColor(0xFFFFFF00);
  mPaint.setStyle(Paint.Style.STROKE);
  mPaint.setStrokeJoin(Paint.Join.ROUND);
  mPaint.setStrokeCap(Paint.Cap.ROUND);
  mPaint.setStrokeWidth(3);
  }

On your SurfaceView

@Override
public boolean onTouchEvent(MotionEvent event) {
  synchronized (_thread.getSurfaceHolder()) {
    if(event.getAction() == MotionEvent.ACTION_DOWN){
      path = new Path();
      path.moveTo(event.getX(), event.getY());
      path.lineTo(event.getX(), event.getY());
    }else if(event.getAction() == MotionEvent.ACTION_MOVE){
      path.lineTo(event.getX(), event.getY());
    }else if(event.getAction() == MotionEvent.ACTION_UP){
      path.lineTo(event.getX(), event.getY());
      _graphics.add(path);
    }
    return true;
  }
}
@Override
public void onDraw(Canvas canvas) {
  for (Path path : _graphics) {
    //canvas.drawPoint(graphic.x, graphic.y, mPaint);
    canvas.drawPath(path, mPaint);
  }
}

Explanation

We create a path and start that path when the MotionEvent is down, or when the user first touch the screen, then add a lineTo, the x and y when the user moves his fingers.

Then stop and push the path we had build to our array of Paths.
 public boolean onTouchEvent(MotionEvent event) { .... }

 Then during the draw function we loop through the array and print them on our canvas.
 public void onDraw(Canvas canvas) { ... }