UIView - (shadowColor &shadowOffset & shadowOpacity & shadowRadius)属性

_imageView1.layer.shadowColor = [UIColor yellowColor].CGColor;//shadowColor阴影颜色
_imageView1.layer.shadowOffset = CGSizeMake(0,0);//shadowOffset阴影偏移，默认(0, -3),这个跟shadowRadius配合使用
_imageView1.layer.shadowOpacity = 1;//阴影透明度，默认0
_imageView1.layer.shadowRadius = 3;//阴影半径，默认3

//路径阴影
UIBezierPath *path = [UIBezierPath bezierPath];

float width = _imageView1.bounds.size.width;
float height = _imageView1.bounds.size.height;
float x = _imageView1.bounds.origin.x;
float y = _imageView1.bounds.origin.y;
float addWH = 10;

CGPoint topLeft      = _imageView1.bounds.origin;
CGPoint topMiddle = CGPointMake(x+(width/2),y-addWH);
CGPoint topRight     = CGPointMake(x+width,y);

CGPoint rightMiddle = CGPointMake(x+width+addWH,y+(height/2));

CGPoint bottomRight  = CGPointMake(x+width,y+height);
CGPoint bottomMiddle = CGPointMake(x+(width/2),y+height+addWH);
CGPoint bottomLeft   = CGPointMake(x,y+height);

CGPoint leftMiddle = CGPointMake(x-addWH,y+(height/2));

[path moveToPoint:topLeft];

//添加四个二元曲线
[path addQuadCurveToPoint:topRight
controlPoint:topMiddle];
[path addQuadCurveToPoint:bottomRight
controlPoint:rightMiddle];
[path addQuadCurveToPoint:bottomLeft
controlPoint:bottomMiddle];
[path addQuadCurveToPoint:topLeft
controlPoint:leftMiddle];

//设置阴影路径
_imageView1.layer.shadowPath = path.CGPath;