文章预读
根据文中提到的解决内存问题有这重要的两点：
①尽量不用drawRect进行绘图
②如果要用，也尽量减小画布
第一点中我们采用何种方式来代替呢，最好是用CAShapLayer，然后配合UIBezierPath来做。
贴一段代码看下：
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(point1X, point1Y)];
[path addLineToPoint:CGPointMake(point2X, point2Y)];
[path addLineToPoint:CGPointMake(point3X, point3Y)];
[path addLineToPoint:CGPointMake(point4X, point4Y)];
[path closePath];
//[path fill];
CAShapeLayer *shapeLayer = [[CAShapeLayer alloc] init];
shapeLayer.path = path.CGPath;
shapeLayer.fillColor = randomColor.CGColor;
shapeLayer.lineCap = kCALineCapRound;
shapeLayer.lineJoin = kCALineJoinRound;
shapeLayer.strokeColor = [UIColor clearColor].CGColor;
shapeLayer.lineWidth = path.lineWidth;
[self.layer addSublayer:shapeLayer];
附录
