目前实现的画板功能，大部分都是继承于UIView的，很少有继承于UIImageView。其实实现方式也不难，就是自己手动重绘下。下面直接代码解释。

首先，定义两个点的变量。

CGPoint prePoint;

    CGPoint curPoint;

其次，对这两个点初始化。

curPoint = CGPointZero;

    prePoint = CGPointZero;

接下来，通过Touch event的几个方法，来记录点的位置。

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event ；

- (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event ；

- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event  ；

- (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event ；

后面，编写绘制方法。

UIGraphicsBeginImageContext( self.frame.size);

[imageToDraw drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];

CGContextSaveGState(UIGraphicsGetCurrentContext());

CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);

CGContextSetLineWidth(UIGraphicsGetCurrentContext(), fPenSize );

CGContextSetStrokeColorWithColor( UIGraphicsGetCurrentContext() , [ [ UIColor whiteColor ] CGColor]);

CGContextSetFillColorWithColor( UIGraphicsGetCurrentContext() , [ [ UIColor whiteColor ] CGColor]);

CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1 , 1 , 1 , 1.0);

CGMutablePathRef path = CGPathCreateMutable();

CGPathMoveToPoint(path,nil, startPoint.x, startPoint.y);

CGPathAddLineToPoint(path,nil, endPoint.x, endPoint.y);

CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear );

CGContextAddPath(UIGraphicsGetCurrentContext(), path);

CGContextStrokePath(UIGraphicsGetCurrentContext());

imageToDraw = UIGraphicsGetImageFromCurrentImageContext();

CGContextRestoreGState(UIGraphicsGetCurrentContext());

UIGraphicsEndImageContext();

该方法需要在touchesMoved、touchesEnded中调用。这样就实现绘制了。

下面，上图。

最后，放一下我的Demo地址，ImageDrawBoard，欢迎提供宝贵的意见或者建议。