swift 中 as、as!、as? 这三种类型转换操作符的异同 及一些控件用法

转自:http://www.111cn.net/sj/iOS/104115.htm

应网友要求，我这里总结了下 as、as!、as? 这三种类型转换操作符的异同，以及各自的使用场景。

1，as使用场合

（1）从派生类转换为基类，向上转型（upcasts）

class Animal {}
class Cat: Animal {}
let cat = Cat()
let animal = cat as Animal

（2）消除二义性，数值类型转换

let num1 = 42 as CGFloat
let num2 = 42 as Int
let num3 = 42.5 as Int
let num4 = (42 / 2) as Double

（3）switch 语句中进行模式匹配

如果不知道一个对象是什么类型，你可以通过switch语法检测它的类型，并且尝试在不同的情况下使用对应的类型进行相应的处理。

switch animal {
case let cat as Cat:
    print("如果是Cat类型对象，则做相应处理")
case let dog as Dog:
    print("如果是Dog类型对象，则做相应处理")
default: break
}

2，as!使用场合

向下转型（Downcasting）时使用。由于是强制类型转换，如果转换失败会报 runtime 运行错误。

class Animal {}
class Cat: Animal {}
let animal :Animal  = Cat()
let cat = animal as! Cat

3，as?使用场合

as? 和 as! 操作符的转换规则完全一样。但 as? 如果转换不成功的时候便会返回一个 nil 对象。成功的话返回可选类型值（optional），需要我们拆包使用。
由于 as? 在转换失败的时候也不会出现错误，所以对于如果能确保100%会成功的转换则可使用 as!，否则使用 as?

let animal:Animal = Cat()
 
if let cat = animal as? Cat{
    print("cat is not nil")
} else {
    print("cat is nil")
}

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

           

（4）这里排序的上下箭头不是图片，而是使用 Font Awesome 图标字体库。优点是可以很轻松地设置颜色和大小，而不会失真

3，项目代码
（代码中高亮部分表示新增的排序相关的代码） 

-- UICollectionGridViewController.swift（组件类） ---

import Foundation
import UIKit
 
//表格排序协议
protocol UICollectionGridViewSortDelegate {
    func sort(colIndex: Int, asc: Bool, rows: [[AnyObject]]) -> [[AnyObject]]
}
 
//多列表格组件（通过CollectionView实现）
class UICollectionGridViewController: UICollectionViewController {
    //表头数据
    var cols: [String]! = []
    //行数据
    var rows: [[AnyObject]]! = []
     
    //排序代理
    var sortDelegate: UICollectionGridViewSortDelegate!
    //选中的表格列（-1表示没有选中的）
    private var selectedColIdx = -1
    //列排序顺序
    private var asc = true
    //单元格内容居左时的左侧内边距
    private var cellPaddingLeft:CGFloat = 5
     
    init() {
        //初始化表格布局
        let layout = UICollectionGridViewLayout()
        super.init(collectionViewLayout: layout)
        layout.viewController = self
        collectionView!.backgroundColor = UIColor.whiteColor()
        collectionView!.registerClass(UICollectionViewCell.self,
            forCellWithReuseIdentifier: "cell")
        collectionView!.delegate = self
        collectionView!.dataSource = self
        collectionView!.directionalLockEnabled = true
        collectionView!.contentInset = UIEdgeInsetsMake(0, 10, 0, 10)
        collectionView!.bounces = false
    }
     
    required init?(coder aDecoder: NSCoder) {
        fatalError("UICollectionGridViewController.init(coder:) has not been implemented")
    }
     
    //设置列头数据
    func setColumns(columns: [String]) {
        cols = columns
    }
     
    //添加行数据
    func addRow(row: [AnyObject]) {
        rows.append(row)
        collectionView!.collectionViewLayout.invalidateLayout()
        collectionView!.reloadData()
    }
     
    override func viewDidLoad() {
        super.viewDidLoad()
    }
     
    override func viewDidLayoutSubviews() {
        collectionView!.frame = CGRectMake(0, 0, view.frame.width, view.frame.height)
    }
     
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
     
    //返回表格总行数
    override func numberOfSectionsInCollectionView(collectionView: UICollectionView)
        -> Int {
        if cols.isEmpty {
            return 0
        }
        //总行数是：记录数＋1个表头
        return rows.count + 1
    }
     
    //返回表格的列数
    override func collectionView(collectionView: UICollectionView,
        numberOfItemsInSection section: Int) -> Int {
        return cols.count
    }
     
    //单元格内容创建
    override func collectionView(collectionView: UICollectionView,
        cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cell",
            forIndexPath: indexPath) as UICollectionViewCell
        //单元格边框
        cell.layer.borderWidth = 1
        cell.backgroundColor = UIColor.whiteColor()
        cell.clipsToBounds = true
         
        //先清空内部原有的元素
        for subview in cell.subviews {
            subview.removeFromSuperview()
        }
         
        //添加内容标签
        let label = UILabel(frame: CGRectMake(0, 0, cell.frame.width, cell.frame.height))
         
        //第一列的内容左对齐，其它列内容居中
        if indexPath.row != 0 {
            label.textAlignment = NSTextAlignment.Center
        }else {
            label.textAlignment = NSTextAlignment.Left
            label.frame.origin.x = cellPaddingLeft
        }
         
        //设置列头单元格，内容单元格的数据
        if indexPath.section == 0 {
            let text = NSAttributedString(string: cols[indexPath.row], attributes: [
                NSUnderlineStyleAttributeName:NSUnderlineStyle.StyleSingle.rawValue,
                NSFontAttributeName:UIFont.boldSystemFontOfSize(15)
                ])
            label.attributedText = text
        } else {
            label.font = UIFont.systemFontOfSize(15)
            label.text = "(rows[indexPath.section-1][indexPath.row])"
        }
        cell.addSubview(label)
         
        //列排序
        if indexPath.row == selectedColIdx {
            //排序列的单元格背景会变色
            cell.backgroundColor = UIColor(red: 122/255, green: 186/255, blue: 255/255,
                alpha: 1)
            //排序列列头显示升序降序图标，并调整列头标签相关位置
            if indexPath.section == 0 {
                let imageWidth: CGFloat = 14
                let imageHeight: CGFloat = 14
                let labelHeight = label.frame.height
                label.sizeToFit()
                label.frame = CGRectMake(cellPaddingLeft, 0, min(label.frame.width,
                    cell.frame.width - imageWidth), labelHeight)
      
                let iconType = asc ? FAType.FALongArrowUp : FAType.FALongArrowDown
                let imageView = UIImageView()
                imageView.frame = CGRectMake(label.frame.width+3,
                    cell.frame.height/2 - imageHeight/2, imageWidth, imageHeight)
                 
                imageView.setFAIconWithName(iconType, textColor: UIColor.blueColor())
                 cell.addSubview(imageView)
            }
        }
        return cell
    }
     
    //单元格选中事件
    override func collectionView(collectionView: UICollectionView,
        didSelectItemAtIndexPath indexPath: NSIndexPath) {
        //打印出点击单元格的［行,列］坐标
        print("点击单元格的[行,列]坐标: [(indexPath.section),(indexPath.row)]")
        if indexPath.section == 0 && sortDelegate != nil {
            //如果点击的是表头单元格，则默认该列升序排列，再次点击则变降序排列，以此交替
            asc = (selectedColIdx != indexPath.row) ? true : !asc
            selectedColIdx = indexPath.row
            rows = sortDelegate.sort(indexPath.row, asc: asc, rows: rows)
            collectionView.reloadData()
        }
    }
}

--- UICollectionGridViewLayout.swift（布局类） ---

import Foundation
import UIKit
 
//多列表格组件布局类
class UICollectionGridViewLayout: UICollectionViewLayout {
    private var itemAttributes: [[UICollectionViewLayoutAttributes]] = []
    private var itemsSize: [NSValue] = []
    private var contentSize: CGSize = CGSizeZero
    //表格组件视图控制器
    var viewController: UICollectionGridViewController!
     
    //准备所有view的layoutAttribute信息
    override func prepareLayout() {
        if collectionView!.numberOfSections() == 0 {
            return
        }
         
        var column = 0
        var xOffset: CGFloat = 0
        var yOffset: CGFloat = 0
        var contentWidth: CGFloat = 0
        var contentHeight: CGFloat = 0
         
        if itemAttributes.count > 0 {
            for var section = 0; section < collectionView?.numberOfSections(); section++ {
                let numberOfItems = collectionView?.numberOfItemsInSection(section)
                for var index = 0; index < numberOfItems; index++ {
                    if section != 0 && index != 0 {
                        continue
                    }
                     
                    let attributes = layoutAttributesForItemAtIndexPath(
                        NSIndexPath(forItem: index, inSection: section))!
                    if section == 0 {
                        var frame = attributes.frame
                        frame.origin.y = collectionView!.contentOffset.y
                        attributes.frame = frame
                    }
                }
            }
            return
        }
         
        itemAttributes = []
        itemsSize = []
         
        if itemsSize.count != viewController.cols.count {
            calculateItemsSize()
        }
         
        for var section = 0; section < collectionView?.numberOfSections(); section++ {
            var sectionAttributes: [UICollectionViewLayoutAttributes] = []
            for var index = 0; index < viewController.cols.count; index++ {
                let itemSize = itemsSize[index].CGSizeValue()
                 
                let indexPath = NSIndexPath(forItem: index, inSection: section)
                let attributes = UICollectionViewLayoutAttributes(forCellWithIndexPath:
                    indexPath)
                //除第一列，其它列位置都左移一个像素，防止左右单元格间显示两条边框线
                if index == 0{
                    attributes.frame = CGRectIntegral(CGRectMake(xOffset, yOffset,
                        itemSize.width, itemSize.height))
                }else {
                    attributes.frame = CGRectIntegral(CGRectMake(xOffset-1, yOffset,
                        itemSize.width+1, itemSize.height))
                }
                 
                if section == 0 && index == 0 {
                    attributes.zIndex = 1024
                } else if section == 0 || index == 0 {
                    attributes.zIndex = 1023
                }
                 
                if section == 0 {
                    var frame = attributes.frame
                    frame.origin.y = collectionView!.contentOffset.y
                    attributes.frame = frame
                }
                 
                sectionAttributes.append(attributes)
                 
                xOffset = xOffset+itemSize.width
                column++
                 
                if column == viewController.cols.count {
                    if xOffset > contentWidth {
                        contentWidth = xOffset
                    }
                     
                    column = 0
                    xOffset = 0
                    yOffset += itemSize.height
                }
            }
            itemAttributes.append(sectionAttributes)
        }
         
        let attributes = itemAttributes.last!.last! as UICollectionViewLayoutAttributes
        contentHeight = attributes.frame.origin.y + attributes.frame.size.height
        contentSize = CGSizeMake(contentWidth, contentHeight)
    }
     
    //需要更新layout时调用
    override func invalidateLayout() {
        itemAttributes = []
        itemsSize = []
        contentSize = CGSizeZero
        super.invalidateLayout()
    }
     
    // 返回内容区域总大小，不是可见区域
    override func collectionViewContentSize() -> CGSize {
        return contentSize
    }
     
    // 这个方法返回每个单元格的位置和大小
    override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath)
        -> UICollectionViewLayoutAttributes? {
         return itemAttributes[indexPath.section][indexPath.row]
    }
     
    // 返回所有单元格位置属性
    override func layoutAttributesForElementsInRect(rect: CGRect)
        -> [UICollectionViewLayoutAttributes]? {
        var attributes: [UICollectionViewLayoutAttributes] = []
        for section in itemAttributes {
            attributes.appendContentsOf(section.filter(
                {(includeElement: UICollectionViewLayoutAttributes) -> Bool in
                return CGRectIntersectsRect(rect, includeElement.frame)
            }))
        }
        return attributes
    }
     
    //当边界发生改变时，是否应该刷新布局。
    //本例在宽度变化时，将重新计算需要的布局信息。
    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        let oldBounds = self.collectionView?.bounds
        if CGRectGetWidth(oldBounds!) != CGRectGetWidth(newBounds) {
            return true
        }else {
            return false
        }
    }
     
    //计算所有单元格的尺寸（每一列各一个单元格）
    func calculateItemsSize() {
        var remainingWidth = collectionView!.frame.width -
            collectionView!.contentInset.left - collectionView!.contentInset.right
         
        for var index = viewController.cols.count-1; index >= 0; index-- {
            let newItemSize = sizeForItemWithColumnIndex(index,
                remainingWidth: remainingWidth)
            remainingWidth -= newItemSize.width
            let newItemSizeValue = NSValue(CGSize: newItemSize)
            //由于遍历列的时候是从尾部开始遍历了，因此将结果插入数组的时候都是放人第一个位置
            itemsSize.insert(newItemSizeValue, atIndex: 0)
        }
    }
     
    //计算某一列的单元格尺寸
    func sizeForItemWithColumnIndex(columnIndex: Int, remainingWidth: CGFloat) -> CGSize {
        let columnString = viewController.cols[columnIndex]
        //根据列头标题文件，估算各列的宽度
        let size = NSString(string: columnString).sizeWithAttributes([
            NSFontAttributeName:UIFont.systemFontOfSize(15),
            NSUnderlineStyleAttributeName:NSUnderlineStyle.StyleSingle.rawValue
            ])
         
        //如果有剩余的空间则都给第一列
        if columnIndex == 0 {
            return CGSizeMake(max(remainingWidth, size.width + 17), size.height + 10)
        }
        //行高增加10像素，列宽增加17像素（为了容纳下排序图表）
        return CGSizeMake(size.width + 17, size.height + 10)
    }
}

--- ViewController.swift（测试类） ---

import UIKit
 
class ViewController: UIViewController, UICollectionGridViewSortDelegate {
     
    var gridViewController: UICollectionGridViewController!
     
    override func viewDidLoad() {
        super.viewDidLoad()
         
        gridViewController = UICollectionGridViewController()
        gridViewController.setColumns(["客户", "消费金额", "消费次数", "满意度"])
        gridViewController.addRow(["hangge", "100", "8", "60%"])
        gridViewController.addRow(["张三", "223", "16", "81%"])
        gridViewController.addRow(["李四", "143", "25", "93%"])
        gridViewController.addRow(["王五", "75", "2", "53%"])
        gridViewController.addRow(["韩梅梅", "43", "12", "33%"])
        gridViewController.addRow(["李雷", "33", "27", "45%"])
        gridViewController.addRow(["王大力", "33", "22", "15%"])
        gridViewController.sortDelegate = self
        view.addSubview(gridViewController.view)
    }
     
    override func viewDidLayoutSubviews() {
        gridViewController.view.frame = CGRectMake(0, 50, view.frame.width,
            view.frame.height-60)
    }
     
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
         
    }
     
    //表格排序函数
    func sort(colIndex: Int, asc: Bool, rows: [[AnyObject]]) -> [[AnyObject]] {
        let sortedRows = rows.sort { (firstRow: [AnyObject], secondRow: [AnyObject])
            -> Bool in
            let firstRowValue = firstRow[colIndex] as! String
            let secondRowValue = secondRow[colIndex] as! String
            if colIndex == 0 {
                //首例姓名使用字典排序法
                if asc {
                    return firstRowValue < secondRowValue
                }
                return firstRowValue > secondRowValue
            } else if colIndex == 1 || colIndex == 2 {
                //中间两列使用数字排序
                if asc {
                    return Int(firstRowValue)! < Int(secondRowValue)!
                }
                return Int(firstRowValue)! > Int(secondRowValue)!
            }
            //最后一列数据先去掉百分号，再转成数字比较
            let firstRowValuePercent = Int(firstRowValue.substringToIndex(
                firstRowValue.endIndex.advancedBy(-1)))
            let secondRowValuePercent = Int(secondRowValue.substringToIndex(
                secondRowValue.endIndex.advancedBy(-1)))
            if asc {
                return firstRowValuePercent < secondRowValuePercent
            }
            return firstRowValuePercent > secondRowValuePercent
             
        }
        return sortedRows
    }
}

UITextField、UITextView组件系统原生就支持文字的复制，但有时我们需要让其他的一些组件也能实现复制功能，比如点击复制UILabel上的文字、UIImageView中的图片、UITableView里单元格的内容、或者点击按钮把文字或图片自动复制到粘贴板中等等。
这些我们借助 UIPasteboard 就可以实现。

一，将内容写入到剪贴板中

1，复制字符串

UIPasteboard.generalPasteboard().string = "欢迎访问 hangge.com"

2，复制字符串数组

UIPasteboard.generalPasteboard().strings = ["hellow", "hangge.com"]

3，复制图片

let image = UIImage(named: "logo.png")
UIPasteboard.generalPasteboard().image = image

4，复制二进制数据（NSData）

let path = NSBundle.mainBundle().pathForResource("logo", ofType: "png")!
let fileData = NSData(contentsOfFile: path)!
UIPasteboard.generalPasteboard().setData(fileData, forPasteboardType: "public.png")

注：从剪贴板获取二进制数据（NSData）

let myData = UIPasteboard.generalPasteboard().dataForPasteboardType("public.png")

二，常见组件增加复制功能

1，让文本标签（UILabel）支持复制功能

我们自定义一个可复制的标签类 UICopyLabel（继承UILabel），其内部能响应 Touch 事件并显示复制菜单

import UIKit
 
class UICopyLabel: UILabel {
     
    override init(frame: CGRect) {
        super.init(frame: frame)
        sharedInit()
    }
     
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        sharedInit()
    }
     
    func sharedInit() {
        userInteractionEnabled = true
        addGestureRecognizer(UILongPressGestureRecognizer(target: self,
            action: "showMenu:"))
    }
     
    func showMenu(sender: AnyObject?) {
        becomeFirstResponder()
        let menu = UIMenuController.sharedMenuController()
        if !menu.menuVisible {
            menu.setTargetRect(bounds, inView: self)
            menu.setMenuVisible(true, animated: true)
        }
    }
     
    //复制
    override func copy(sender: AnyObject?) {
        let board = UIPasteboard.generalPasteboard()
        board.string = text
        let menu = UIMenuController.sharedMenuController()
        menu.setMenuVisible(false, animated: true)
    }
     
    override func canBecomeFirstResponder() -> Bool {
        return true
    }
     
    override func canPerformAction(action: Selector, withSender sender: AnyObject?)
        -> Bool {
        if action == "copy:" {
            return true
        }
        return false
    }
}

在这个文本标签上长按后便可以复制其内容：

2，让图片控件（UIImageView）支持复制、粘贴功能

我们自定义一个图片控件类 UICPImageView（继承UIImageView），内部同样添加Touch事件响应。该控件不仅支持复制，还支持粘贴。

import UIKit
 
class UICPImageView: UIImageView {
 
    override init(frame: CGRect) {
        super.init(frame: frame)
        sharedInit()
    }
     
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        sharedInit()
    }
     
    func sharedInit() {
        userInteractionEnabled = true
        addGestureRecognizer(UILongPressGestureRecognizer(target: self,
            action: "showMenu:"))
    }
     
    func showMenu(sender: AnyObject?) {
        becomeFirstResponder()
        let menu = UIMenuController.sharedMenuController()
        if !menu.menuVisible {
            menu.setTargetRect(bounds, inView: self)
            menu.setMenuVisible(true, animated: true)
        }
    }
     
    //复制
    override func copy(sender: AnyObject?) {
        let board = UIPasteboard.generalPasteboard()
        board.image = self.image
        let menu = UIMenuController.sharedMenuController()
        menu.setMenuVisible(false, animated: true)
    }
     
    //粘贴
    override func paste(sender: AnyObject?) {
        let board = UIPasteboard.generalPasteboard()
        self.image = board.image
        let menu = UIMenuController.sharedMenuController()
        menu.setMenuVisible(false, animated: true)
    }
     
    override func canBecomeFirstResponder() -> Bool {
        return true
    }
     
    override func canPerformAction(action: Selector, withSender sender: AnyObject?)
        -> Bool {
        if action == "copy:" {
            return true
        }else if action == "paste:" {
            return true
        }
        return false
    }
}

下面我们在界面上添加两个 UICPImageView，我们可以把左边控件里的图片复制到右边控件中来，效果图如下：

3，让表格（UITableView）支持复制功能

import UIKit
 
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
     
    var tableView:UITableView?
    var tableData = ["条目1", "条目2", "条目3", "条目4", "条目5", "条目6", "条目7"]
     
    override func loadView() {
        super.loadView()
    }
     
    override func viewDidLoad() {
        super.viewDidLoad()
         
        //创建表视图
        self.tableView = UITableView(frame: self.view.frame, style:.Plain)
        self.tableView!.delegate = self
        self.tableView!.dataSource = self
        //创建一个重用的单元格
        self.tableView!.registerClass(UITableViewCell.self,
            forCellReuseIdentifier: "SwiftCell")
        self.view.addSubview(self.tableView!)
    }
     
    func tableView(tableView: UITableView, performAction action: Selector,
        forRowAtIndexPath indexPath: NSIndexPath, withSender sender: AnyObject?) {
            let board = UIPasteboard.generalPasteboard()
            board.string = tableData[indexPath.row]
    }
     
    func tableView(tableView: UITableView, canPerformAction action: Selector,
        forRowAtIndexPath indexPath: NSIndexPath, withSender sender: AnyObject?) -> Bool {
            if action == "copy:" {
                return true
            }
            return false
    }
     
    func tableView(tableView: UITableView,
        shouldShowMenuForRowAtIndexPath indexPath: NSIndexPath) -> Bool {
        return true
    }
     
    //在本例中，只有一个分区
    func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1;
    }
     
    //返回表格行数（也就是返回控件数）
    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return tableData.count
    }
     
    //创建各单元显示内容(创建参数indexPath指定的单元）
    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath)
        -> UITableViewCell
    {
        //为了提供表格显示性能，已创建完成的单元需重复使用
        let identify:String = "SwiftCell"
        //同一形式的单元格重复使用，在声明时已注册
        let cell = tableView.dequeueReusableCellWithIdentifier(identify,
            forIndexPath: indexPath) as UITableViewCell
        cell.accessoryType = UITableViewCellAccessoryType.DisclosureIndicator
        cell.textLabel?.text = tableData[indexPath.row]
        return cell
    }
     
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

长按某个单元格即可复制这个单元格内容：

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