UIImage 虚线框 可以用作 UITextfield、UIButton 的background，

1.方法一、

//size是背景图尺寸，border color是边框颜色，border width是边框大小。

extension UIImage {

class public
func getImageWithLineBroken(size:CGSize,borderColor:UIColor,borderWidth:CGFloat) ->
UIImage {

UIGraphicsBeginImageContextWithOptions(size,
false,
0.0);

UIColor.clearColor().set()

let context =
UIGraphicsGetCurrentContext();

CGContextBeginPath(context);

CGContextSetLineWidth(context, borderWidth);

CGContextSetStrokeColorWithColor(context, borderColor.CGColor);

let lengths:[CGFloat] = [3,
1];

CGContextSetLineDash(context,
0, lengths, 1);

// line 1

CGContextMoveToPoint(context,
30.0, 0.0);

CGContextAddLineToPoint(context,
170,
0.0);

// line 2

CGContextAddArcToPoint(context,
200 , 30, 170,
60, 30)

// line 3

//CGContextAddLineToPoint(context, 200, 30);

// line 4

CGContextAddLineToPoint(context,
170,
60);

CGContextAddLineToPoint(context,
30,
60);

CGContextAddArcToPoint(context,
0 , 30, 30,
0, 30)

CGContextAddLineToPoint(context,
30,
0);

// CGContextAddArc(context, 170, 30, 30, CGFloat(M_PI * 270/180), CGFloat(M_PI_2), 0)

// //CGContextMoveToPoint(context, 170, 60);

// CGContextAddLineToPoint(context, 30, 60);

//

// CGContextAddArc(context, 30, 30, 30, CGFloat(M_PI_2), CGFloat(M_PI * 270/180), 0)

// CGContextMoveToPoint(context, 170, 60);

CGContextStrokePath(context);

let image =
UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image

}