实现机制
在每一View的layer层中有一个mask属性，他就是专门来设置该View的遮罩效果的。该mask本身也是一个layer层。我们只需要生成一个自定义的layer，然后覆盖在需要遮罩的View上面即可。问题就归于如何生成入上图所示的不规则图片的Layer。CAShapeLayer可以根据几个点的依次连线，产生一个闭合空间的layer。
实现方法
实现一个CAShapeLayer的Category。
+ (instancetype)createMaskLayerWithView : (UIView *)view{
CGFloat viewWidth = CGRectGetWidth(view.frame);
CGFloat viewHeight = CGRectGetHeight(view.frame);
CGFloat rightSpace = 10;
CGFloat topSpace = 10;
CGFloat radius = 10;
CGPoint point1 = CGPointMake(0, radius);
CGPoint point2 = CGPointMake(radius, 0);
CGPoint point3 = CGPointMake(viewWidth-rightSpace-radius, 0);
CGPoint point4 = CGPointMake(viewWidth-rightSpace, topSpace);
CGPoint point5 = CGPointMake(viewWidth, topSpace);
CGPoint point6 = CGPointMake(viewWidth-rightSpace, topSpace+10);
CGPoint point7 = CGPointMake(viewWidth-rightSpace, viewHeight-radius);
CGPoint point8 = CGPointMake(viewWidth-rightSpace-radius, viewHeight);
CGPoint point9 = CGPointMake(radius, viewHeight);
CGPoint point10 = CGPointMake(0, viewHeight-radius);
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:point1];
[path addArcWithCenter:CGPointMake(radius, radius) radius:radius startAngle:M_PI endAngle:M_PI*1.5 clockwise:YES];
[path addLineToPoint:point2];
[path addLineToPoint:point3];
[path addArcWithCenter:CGPointMake(viewWidth-2*radius, radius) radius:radius startAngle:M_PI*1.5 endAngle:0 clockwise:YES];
[path addLineToPoint:point4];
[path addLineToPoint:point5];
[path addLineToPoint:point6];
[path addLineToPoint:point7];
[path addArcWithCenter:CGPointMake(viewWidth-2*radius, viewHeight-radius) radius:radius startAngle:0 endAngle:M_PI*0.5 clockwise:YES];
[path addLineToPoint:point8];
[path addLineToPoint:point9];
[path addArcWithCenter:CGPointMake(radius, viewHeight-radius) radius:radius startAngle:M_PI*0.5 endAngle:M_PI clockwise:YES];
[path addLineToPoint:point10];
[path closePath];
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = path.CGPath;
return layer;
}
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(40, 50, 200, 40)];
view.backgroundColor = [UIColor orangeColor];
CAShapeLayer *layer = [CAShapeLayer createMaskLayerWithView:view];
view.layer.mask = layer;
[self.view addSubview:view];
参数说明
center：Specifies the center point of the circle (in the current coordinate system) used to define the arc.
radius：Specifies the radius of the circle used to define the arc.
startAngle： Specifies the starting angle of the arc (measured in radians).
endAngle：Specifies the end angle of the arc (measured in raians).
clockwise：The direction in which to draw the arc.
实现效果如下图：
