Swift小技巧(五)

目录

• 利用谓语语法和正则表达式，判断字符串是否符合特定格式
• 如何判断app运行在真机还是模拟器上面
• OC的respondsToSelector方法
• 获得某个date的年月日时分秒等
• 给UITextView添加placeholder占位符
• 格式化输出Int
• 搜索指定的文件夹路劲
• 获得app设置中version版本号
• 设置tableview的分割线separator的颜色，宽度等
• 如何安全的使用array，如果下标越界等情况发生时，不会崩溃
• iOS自带的tableview刷新控件
• 如何获得一个view的快照，并生成image
• 快速比较，两个date之间的差距，比如相差多少年月日等

利用谓语语法和正则表达式，判断字符串是否符合特定格式

 //利用谓语语法，判断一个字符串是否是邮箱。
func isValidEmail(testStr: String) -> Bool {
    //可以根据自己的需要改成别的正则表达式
    let emailRegex = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}"
    let emailTest = NSPredicate(format: "SELF MATCHES %@", emailRegex)
    return emailTest.evaluate(with: testStr)
}
isValidEmail(testStr: "213@12.com")//true

如何判断app运行在真机还是模拟器上面

 #if (arch(i386) || arch(x86_64)) && os(iOS)
    //如果是模拟器，则会运行，真机上面则不会执行
    print("模拟器")
#endif
    print("正常代码")

OC的respondsToSelector方法

 //使用如下方式代替
if let delegate = delegate {//判断是否存在代理
    if let theMethod = delegate.theOptionalProtocolMethod? {//判断代理是否实现方法
        theMethod()
        return
    }
}

获得某个date的年月日时分秒等

 let date = Date()
//获得当天的日历对象
let calendar = Calendar.current
//获得小时
let hour = calendar.component(.hour, from: date)
//获得分钟
let minutes = calendar.component(.minute, from: date)

给UITextView添加placeholder占位符

 //定义了一个全局的常量
let placeholderText = "请输入内容！"
//1.给textview扩展如下方法：
extension UITextView {
    func addPlaceholderText(text: String) {
        self.text = text
        self.textColor = .lightGray
    }
}
//2.创建出textview
        textView = UITextView(frame: view.frame)
        textView.delegate = self
        textView.addPlaceholderText(text: placeholderText)
        view.addSubview(textView)
//3.在textview的下列代理方法中，实现如下两个方法，添加如下代码
    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == .lightGray {
            textView.text = nil
            textView.textColor = .black
        }
    }
    
    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
            textView.addPlaceholderText(text: placeholderText)
        }
    }

只需要以上操作，textview就可以跟textfield一样，拥有一个placeholder占位符提示语

格式化输出Int

 //方法一：
let str = String(format: "%02d-%03d", 1,2)//01-002

//方法二
let str2 = String(format: "%02d-%03d", arguments: [1,2])//01-002

//方法三
let formatter = NumberFormatter()
formatter.minimumIntegerDigits = 2
let str3 = formatter.string(from: 1)//01

搜索指定的文件夹路劲

 let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]

获得app设置中version版本号

 let verson = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as! String
print(version)//1.0.1

设置tableview的分割线separator的颜色，宽度等

tableView.separatorColor = .red//分割线颜色
tableView.separatorStyle = .singleLineEtched//分割线样式
//        tableView.separatorEffect//效果
tableView.separatorInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)//分割线内边距，都设置为0，则会出现一条宽等于屏幕的完整的分割线

如何安全的使用array，如果下标越界等情况发生时，不会崩溃

 //给collection扩展一个下标方法
extension Collection where Indices.Iterator.Element == Index {
    subscript (safe index: Index) -> Generator.Element? {
        return indices.contains(index) ? self[index] : nil
    }
}
//使用
let arr = [1]
arr[safe: 2]//nil，会得到一个nil，而不会崩溃

iOS自带的tableview刷新控件

 //创建出刷新控件
        let refreshControl = UIRefreshControl()
        refreshControl.attributedTitle = NSAttributedString(string: "开始刷新")
        refreshControl.addTarget(self, action: #selector(refresh(sender:)), for: .valueChanged)
        //添加上去即可
        tableView.addSubview(refreshControl)

//实现刷新函数
    func refresh(sender: AnyObject) {
        //做刷新要做的事情
        print("开始刷新")
    }
        
        //结束刷新，需要结束的时候调用
        refreshControl.endRefreshing()

如何获得一个view的快照，并生成image

 extension UIView {
    func takeSnapshot() -> UIImage {
        UIGraphicsBeginImageContextWithOptions(bounds.size, false, UIScreen.main.scale)
        drawHierarchy(in: self.bounds, afterScreenUpdates: true)
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return image
    }
}

快速比较，两个date之间的差距，比如相差多少年月日等

 extension Date {
    //返回相差多少年
    func years(from date: Date) -> Int {
        return Calendar.current.dateComponents([.year], from: date, to: self).year ?? 0
    }
    //返回差多少月
    func months(from date: Date) -> Int {
        return Calendar.current.dateComponents([.month], from: date, to: self).month ?? 0
    }
    //返回差多少周
    func weeks(from date: Date) -> Int {
        return Calendar.current.dateComponents([.weekOfMonth], from: date, to: self).weekOfMonth ?? 0
    }
    //返回差多少天
    func days(from date: Date) -> Int {
        return Calendar.current.dateComponents([.day], from: date, to: self).day ?? 0
    }
    //返回差多少小时
    func hours(from date: Date) -> Int {
        return Calendar.current.dateComponents([.hour], from: date, to: self).hour ?? 0
    }
    //返回差多少分钟
    func minutes(from date: Date) -> Int {
        return Calendar.current.dateComponents([.minute], from: date, to: self).minute ?? 0
    }
    //返回差多少秒
    func seconds(from date: Date) -> Int {
        return Calendar.current.dateComponents([.second], from: date, to: self).second ?? 0
    }
    //返回差距的描述
    func offset(from date: Date) -> String {
        if years(from: date)   > 0 { return "(years(from: date))y"   }
        if months(from: date)  > 0 { return "(months(from: date))M"  }
        if weeks(from: date)   > 0 { return "(weeks(from: date))w"   }
        if days(from: date)    > 0 { return "(days(from: date))d"    }
        if hours(from: date)   > 0 { return "(hours(from: date))h"   }
        if minutes(from: date) > 0 { return "(minutes(from: date))m" }
        if seconds(from: date) > 0 { return "(seconds(from: date))s" }
        return ""
    }
}
//使用
let date1 = DateComponents(calendar: .current, year: 2014, month: 11, day: 28, hour: 5, minute: 9).date!
let date2 = DateComponents(calendar: .current, year: 2015, month: 8, day: 28, hour: 5, minute: 9).date!

let years = date2.years(from: date1)     // 0
let months = date2.months(from: date1)   // 9
let weeks = date2.weeks(from: date1)     // 39
let days = date2.days(from: date1)       // 273
let hours = date2.hours(from: date1)     // 6,553
let minutes = date2.minutes(from: date1) // 393,180
let seconds = date2.seconds(from: date1) // 23,590,800

let timeOffset = date2.offset(from: date1) // "9M"

let date3 = DateComponents(calendar: .current, year: 2014, month: 11, day: 28, hour: 5, minute: 9).date!
let date4 = DateComponents(calendar: .current, year: 2015, month: 11, day: 28, hour: 5, minute: 9).date!

let timeOffset2 = date4.offset(from: date3) // "1y"

let date5 = DateComponents(calendar: .current, year: 2017, month: 4, day: 28).date!
let now = Date()
let timeOffset3 = now.offset(from: date5) // "1w"

//或者使用date components formatter
let dateComponentsFormatter = DateComponentsFormatter()
dateComponentsFormatter.allowedUnits = [.year,.month,.weekOfYear,.day,.hour,.minute,.second]
dateComponentsFormatter.maximumUnitCount = 1
dateComponentsFormatter.unitsStyle = .full
dateComponentsFormatter.string(from: Date(), to: Date(timeIntervalSinceNow: 4000000))  // "1 month"