Swift 类型转换

Swift: CGFloat 为什么不能转换成 Float

Cannot convert value of type 'CGFloat?' to type 'Float' in coercion

原因：

The Float and CGFloat data types sound so similar you might think they were identical, but they aren't: CGFloat is flexible in that its precision adapts to the type of device it's running on, whereas Float is always a fixed precision. Float和CGFloat数据类型听起来很相似，你可能认为它们是相同的，但它们不是：CGFloat的灵活性在于它的精度适应它运行的设备类型，而Float总是一个固定的精度。

所以CGFloat是更加广泛的一种类型，它的兼容性更加好，Float可以转成CGFloat：

var progress:Float = 0.88
var cgFloatValue = CGFloat(progress)

 if progress == CGFloat(1.0) {
 

 }

由于Swift编译器向上兼容特性，在Swift中CGFloat转Float是不被容许的，这一点和访问控制权限很像。

Data相关

Data to Image,Date to Image

    let imgData = UIImage.pngData(self.coverImage?)
    let img = UIImage(data: imgData)

Cannot convert value of type 'Int64?' to expected argument type 'Int'

Int64 to Int

let int64Value: Int64 = 6666888
let intValue = NSNumber(value: int64Value).intValue

String相关

2.1Stirng to URL & URL to String

2.2 String convert to Double/Float

let myString = "666"
let myDouble = (myString as NSString).doubleValue
let myFloat = (myString as NSString).floatValue

2.2 Double/Float/Int convert to String

String("\(doubleValue)")

3.string to NSMutableAttributeString

    let normalStr = prefix + suffix
    let mutableAttributeString = NSMutableAttributedString(string: normalStr)

4. Swift设置字符串NSMutableAttributeString属性：

        let title = "蓝朋友"
        let attributes = [NSAttributedString.Key.font: UIFont.systemFont(ofSize: 8),
                                   NSAttributedString.Key.foregroundColor : UIColor.blue]
        let attributeString = NSMutableAttributedString(string: title, attributes: attributes)
        rightBtn.setAttributedTitle(attributeString, for: .normal)

5. 封装NSMutableAttributedString富文本

NSAttributedString.Key.foregroundColor 和 NSAttributedString.Key.font

    func getAttributeStringWith(_ prefix: String, _ suffix: String) -> NSMutableAttributedString {
        let normalStr = prefix + suffix
        let mutableAttributeString = NSMutableAttributedString(string: normalStr)
        //设置prefix attributes属性
        let prefixAttribute = [NSAttributedString.Key.foregroundColor: UIColor.white,
        NSAttributedString.Key.font: UIFont.systemFont(ofSize: 17)] as [NSAttributedString.Key : Any]
        mutableAttributeString.addAttributes(prefixAttribute, range: NSRange.init(location: 0, length: prefix.count))
        //设置suffix attributes属性
        let suffixAttribute = [NSAttributedString.Key.foregroundColor: UIColor.init(red: 252/255.0, green: 46/255.0, blue: 117/255.0, alpha: 1),
                         NSAttributedString.Key.font: UIFont.systemFont(ofSize: 25, weight: .bold)] as [NSAttributedString.Key: Any]
        mutableAttributeString.addAttributes(suffixAttribute, range: NSRange.init(location: prefix.count, length: suffix.count))
        
        return mutableAttributeString
    }

6.KVO 监听属性currentIndex

forKeyPath:@"currentIndex" options:5 context:0x0] was sent to an object that is not KVC-compliant for the "DetailVideoIndex" property.'

原因是KVO需要使用OC runtime动态性。定义如下：

@objc dynamic var currentIndex: NSInteger = 0

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "currentIndex" {
            //do what you want
        }

//Swift数组转json

func getJSONStringFromArray(array:Array<Any>) -> String {
    if (!JSONSerialization.isValidJSONObject(array)) {
        print("无法解析出JSONString")
        return ""
    }
    let data : NSData! = try? JSONSerialization.data(withJSONObject: array, options: []) as NSData?
    let JSONString = NSString(data:data as Data,encoding: String.Encoding.utf8.rawValue)
    return JSONString! as String
}

//json转数组

func getArrayFromJSONString(jsonString:String) -> Array<Any>{
    let jsonData:Data = jsonString.data(using: .utf8)!
    let array = try? JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers)
    if array != nil {
        return array as! Array
    }
    return array as! Array
}