Swift4.2 API的变化

1、通知

NotificationCenter.default.addObserver(self,
            selector: #selector(KMPlaceholderTextView.textDidChange),
            name: NSNotification.Name.UITextViewTextDidChange,
            object: nil)
改成
NotificationCenter.default.addObserver(self,
            selector: #selector(KMPlaceholderTextView.textDidChange),
            name: UITextView.textDidChangeNotification,
            object: nil)

2、压缩图片质量

let imageData = UIImageJPEGRepresentation(img, 0.25)!
改成
let imageData = img.jpegData(compressionQuality: 0.25)!