APIDemo -> Graphics ->FingerPaint 참고하시면 해결하실거같아요

class PView extends View implements View.OnTouchListener {
		private static final String TAG = "DrawView";


		private static final float MINP = 0.25f;
		private static final float MAXP = 0.75f;


		private Path    mPath;
		private Paint       mPaint;   
		private ArrayList<Path> paths = new ArrayList<Path>();


		public PView(Context context) {
			super(context);
			setFocusable(true);
			setFocusableInTouchMode(true);


			this.setOnTouchListener(this);


			mPaint = new Paint();
			mPaint.setAntiAlias(true);
			mPaint.setDither(true);
			mPaint.setColor(0xFFFFFFFF);
			mPaint.setStyle(Paint.Style.STROKE);
			mPaint.setStrokeJoin(Paint.Join.ROUND);
			mPaint.setStrokeCap(Paint.Cap.ROUND);
			mPaint.setStrokeWidth(6);
		}               
		@Override
		protected void onSizeChanged(int w, int h, int oldw, int oldh) {
			super.onSizeChanged(w, h, oldw, oldh);
		}


		@Override
		protected void onDraw(Canvas canvas) {            


			for (Path p : paths){
				canvas.drawPath(p, mPaint);
			}
		}


		private float mX, mY;
		private static final float TOUCH_TOLERANCE = 4;


		private void touch_start(float x, float y) {
			mPath = new Path();
			paths.add(mPath);


			mPath.reset();
			mPath.moveTo(x, y);
			mX = x;
			mY = y;
		}
		private void touch_move(float x, float y) {
			float dx = Math.abs(x - mX);
			float dy = Math.abs(y - mY);
			if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
				mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
				mX = x;
				mY = y;
			}
		}
		private void touch_up() {
			mPath.lineTo(mX, mY);
		}






		@Override
		public boolean onTouch(View arg0, MotionEvent event) {
			float x = event.getX();
			float y = event.getY();


			switch (event.getAction()) {
			case MotionEvent.ACTION_DOWN:
				touch_start(x, y);
				invalidate();
				break;
			case MotionEvent.ACTION_MOVE:
				touch_move(x, y);
				invalidate();
				break;
			case MotionEvent.ACTION_UP:
				touch_up();
				invalidate();
				break;
			}
			return true;
		}
	}