這個可能稍微復雜壹點，但是非常實用：
public?class?MainActivity?extends?Activity?{
DrawingView?dv?;
private?PaintmPaint;
private?DrawingManager?mDrawingManager=null;
@Override
protected?void?onCreate(Bundle?savedInstanceState)?{
super.onCreate(savedInstanceState);
dv?=?new?DrawingView(this);
setContentView(dv);
mPaint?=?new?Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.GREEN);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);?
}
public?class?DrawingView?extends?View?{public?int?width;
public?int?height;
private?Bitmap?mBitmap;
private?Canvas?mCanvas;
private?PathmPath;
private?PaintmBitmapPaint;
Context?context;
private?Paint?circlePaint;
private?Path?circlePath;
public?DrawingView(Context?c)?{
super(c);
context=c;
mPath?=?new?Path();
mBitmapPaint?=?new?Paint(Paint.DITHER_FLAG);?
circlePaint?=?new?Paint();
circlePath?=?new?Path();
circlePaint.setAntiAlias(true);
circlePaint.setColor(Color.BLUE);
circlePaint.setStyle(Paint.Style.STROKE);
circlePaint.setStrokeJoin(Paint.Join.MITER);
circlePaint.setStrokeWidth(4f);?
}
@Override
protected?void?onSizeChanged(int?w,?int?h,?int?oldw,?int?oldh)?{super.onSizeChanged(w,?h,?oldw,?oldh);
mBitmap?=?Bitmap.createBitmap(w,?h,?Bitmap.Config.ARGB_8888);
mCanvas?=?new?Canvas(mBitmap);
}
@Override
protected?void?onDraw(Canvas?canvas)?{
super.onDraw(canvas);
canvas.drawBitmap(?mBitmap,?0,?0,?mBitmapPaint);
canvas.drawPath(?mPath,?mPaint);
canvas.drawPath(?circlePath,?circlePaint);
}
private?float?mX,?mY;
private?static?final?float?TOUCH_TOLERANCE?=?4;
private?void?touch_start(float?x,?float?y)?{
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;
circlePath.reset();
circlePath.addCircle(mX,?mY,?30,?Path.Direction.CW);
}
}
private?void?touch_up()?{
mPath.lineTo(mX,?mY);
circlePath.reset();
//?commit?the?path?to?our?offscreen
mCanvas.drawPath(mPath,?mPaint);
//?kill?this?so?we?don't?double?draw
mPath.reset();
}
@Override
public?boolean?onTouchEvent(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;
}?
}
}妳的手指到哪裏，Canvas就畫到哪裏。圖：