swift 截屏、录屏监听、添加水印_screen captured

如果系统未禁止应用截屏，导致应用的关键信息可能会被截屏泄露，通过查看应用截图，可能获取到用户的敏感信息，造成个人资料外泄。
iOS实现不了不让截屏或者录屏，但是提供的截屏或者录屏的监听方法，当用户截屏或录屏时系统会发送相关通知，我们可以提示用户截屏或录屏会泄露一些个人安全信息，类似于微信或支付宝的付款码截屏。

监听通知

监听截屏通知
NotificationCenter.default.addObserver(self, selector: #selector(screenshots), name: UIApplication.userDidTakeScreenshotNotification, object: nil)

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监听屏幕状态通知
NotificationCenter.default.addObserver(self, selector: #selector(screenCaptured), name: UIScreen.capturedDidChangeNotification, object: nil)
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捕获屏幕状态

// 监听录屏通知,iOS 11后才有录屏
if #available(iOS 11.0, *) {
    // 如果正在捕获此屏幕（例如，录制、空中播放、镜像等），则为真
    if UIScreen.main.isCaptured {
       screenCaptured()
    }
}

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提示方法

@objc func screenCaptured(){
     let alertVC = UIAlertController(title: "提示", message: "为保证用户名,密码安全,请不要截屏或录屏!", preferredStyle: .alert)
     let action = UIAlertAction(title: "知道了", style: .default, handler:nil)
     alertVC.addAction(action)
     self.present(alertVC, animated: true, completion: nil);
        
    }
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移除监听

deinit {
     NotificationCenter.default.removeObserver(self, name: UIApplication.userDidTakeScreenshotNotification, object: nil);
     NotificationCenter.default.removeObserver(self, name: UIScreen.capturedDidChangeNotification, object: nil);
        
}
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添加水印

func createWaterMarkFor(Text strTxt:String,
                            andFullSize fsize:CGSize,
                            andCorners corners:UIRectCorner? = nil,
                        withRadius r:CGFloat? = nil) -> UIImage {
    
    //[S] 1、设置水印样式
    let paragraphStyle:NSMutableParagraphStyle = NSMutableParagraphStyle()
    paragraphStyle.lineBreakMode = .byWordWrapping
    paragraphStyle.lineSpacing = 6.0 * 10
    paragraphStyle.alignment = .center
    
    var _attr:[NSAttributedString.Key:Any] = [
        .font : UIFont.systemFont(ofSize: 15, weight: .semibold),
            .foregroundColor:UIColor.init(red: 222/255.0, green: 222/255.0, blue: 222/255.0, alpha: 0.8),
        .paragraphStyle: paragraphStyle,
        .kern:1.0,
    ]
    
    if #available(iOS 14.0, *) {
        _attr[.tracking] = 1.0
    }
    
    let attributedString:NSMutableAttributedString = NSMutableAttributedString.init(string: strTxt)
    let stringRange = NSMakeRange(0, attributedString.string.utf16.count)
    attributedString.addAttributes(_attr,range: stringRange)
    //[E]
    
    //[S] 2、建立水印图
    let _max_value = attributedString.size().width > attributedString.size().height ? attributedString.size().width : attributedString.size().height
    let _size = CGSize.init(width: _max_value + 10, height: _max_value + 10)
    
    //2.1、设置上下文
    if UIScreen.main.scale > 1.5 {
        UIGraphicsBeginImageContextWithOptions(_size,false,0)
    }
    else{
        UIGraphicsBeginImageContext(_size)
    }
    var context = UIGraphicsGetCurrentContext()
    
    //2.2、根据中心开启旋转上下文矩阵
    //将绘制原点（0，0）调整到源image的中心
    context?.concatenate(.init(translationX: _size.width * 0.8, y: _size.height * 0.4))
    
    //以绘制原点为中心旋转45°
    context?.concatenate(.init(rotationAngle: -0.25 * .pi))
    
    //将绘制原点恢复初始值，保证context中心点和image中心点处在一个点(当前context已经发生旋转，绘制出的任何layer都是倾斜的)
    context?.concatenate(.init(translationX: -_size.width * 0.8, y: -_size.height * 0.4))
    
    //2.3、添加水印文本
    attributedString.draw(in: .init(origin: .zero, size: _size))
    
    //2.4、从上下文中获取水印图
    let _waterImg = UIGraphicsGetImageFromCurrentImageContext() ?? UIImage.init()
    //[E]
    
    //[S] 3、重设上下文，建立底图
    if UIScreen.main.scale > 1.5 {
        UIGraphicsBeginImageContextWithOptions(fsize,false,0)
    }
    else{
        UIGraphicsBeginImageContext(fsize)
    }
    context = UIGraphicsGetCurrentContext()
    
    //3.1圆角底图(可选)
    if corners != nil && r != nil && r?.isNaN == false && r?.isFinite != false {
        let rect:CGRect = .init(origin: .zero, size: fsize)
        let bezierPath:UIBezierPath = UIBezierPath.init(roundedRect: rect,
                                                        byRoundingCorners: corners!,
                                                        cornerRadii: CGSize(width: r!, height: r!))
        
        context?.addPath(bezierPath.cgPath)
    }
    
    //3.2 将水印图贴上去
    var _tempC = fsize.width / _waterImg.size.width
    var _maxColumn:Int = _tempC.isNaN || !_tempC.isFinite ? 1 : Int(_tempC)
    if fsize.width.truncatingRemainder(dividingBy: _waterImg.size.width) != 0 {
        _maxColumn += 1
    }
    
    _tempC = fsize.height / _waterImg.size.height
    var _maxRows:Int = _tempC.isNaN || !_tempC.isFinite ? 1 : Int(_tempC)
    if fsize.height.truncatingRemainder(dividingBy: _waterImg.size.height) != 0 {
        _maxRows += 1
    }
    
    for r in 0..<_maxRows {
        for c in 0..<_maxColumn {
            let _rect:CGRect = .init(origin: .init(x: CGFloat(c) * _waterImg.size.width,
                                                   y: CGFloat(r) * _waterImg.size.height),
                                     size: _waterImg.size)
            _waterImg.draw(in: _rect)
        }
    }
    
    //裁剪、透明
    context?.clip()
    context?.setFillColor(UIColor.clear.cgColor)
    context?.fill(.init(origin: .zero, size: fsize))
    
    //3.3 输出最终图形
    let _canvasImg = UIGraphicsGetImageFromCurrentImageContext() ?? UIImage.init()
    //[E]
    
    //4、关闭图形上下文
    UIGraphicsEndImageContext()
    
    return _canvasImg
    
}

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