Swift

想要给图片添加文字水印或者注释，我们需要实现在UIImage上写字的功能。

1，效果图如下：

（在图片左上角和右下角都添加了文字。）

2，为方便使用，我们通过扩展UIImage类来实现添加水印功能

（文字大小，文字颜色，背景色，位置，边距都可以设置）

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//--- UIImageExtension.swift --- import UIKit   extension UIImage{           //水印位置枚举     enum WaterMarkCorner{         case TopLeft         case TopRight         case BottomLeft         case BottomRight     }           //添加水印方法     func waterMarkedImage(waterMarkText:String, corner:WaterMarkCorner = .BottomRight,         margin:CGPoint = CGPoint(x: 20, y: 20), waterMarkTextColor:UIColor = UIColor.whiteColor(),         waterMarkTextFont:UIFont = UIFont.systemFontOfSize(20),         backgroundColor:UIColor = UIColor.clearColor()) -> UIImage{                   let textAttributes = [NSForegroundColorAttributeName:waterMarkTextColor,             NSFontAttributeName:waterMarkTextFont]         let textSize = NSString(string: waterMarkText).sizeWithAttributes(textAttributes)         var textFrame = CGRectMake(0, 0, textSize.width, textSize.height)                   let imageSize = self.size         switch corner{         case .TopLeft:             textFrame.origin = margin         case .TopRight:             textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: margin.y)         case .BottomLeft:             textFrame.origin = CGPoint(x: margin.x, y: imageSize.height - textSize.height - margin.y)         case .BottomRight:             textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x,                 y: imageSize.height - textSize.height - margin.y)         }                   // 开始给图片添加文字水印         UIGraphicsBeginImageContext(imageSize)         self.drawInRect(CGRectMake(0, 0, imageSize.width, imageSize.height))         NSString(string: waterMarkText).drawInRect(textFrame, withAttributes: textAttributes)                   let waterMarkedImage = UIGraphicsGetImageFromCurrentImageContext()         UIGraphicsEndImageContext()                   return waterMarkedImage     } }

3，使用样例

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import UIKit   class ViewController: UIViewController {       @IBOutlet weak var imageView: UIImageView!           override func viewDidLoad() {         super.viewDidLoad()                   //使用链式调用方法，给图片添加两条水印         imageView.image = UIImage(named:"bg")?             .waterMarkedImage("做最好的开发者知识平台")             .waterMarkedImage("hangge.com", corner: .TopLeft,                 margin: CGPoint(x: 20, y: 20), waterMarkTextColor: UIColor.blackColor(),                 waterMarkTextFont: UIFont.systemFontOfSize(45), backgroundColor: UIColor.clearColor())     }       override func didReceiveMemoryWarning() {         super.didReceiveMemoryWarning()     } }