• 注意最下面，为方便使用，我扩展了 UIViewController，添加了个 presentHGImagePicker() 方法，调用后便会出现照片选择组件。
• 虽然上面方法调用时加载的是相簿列表视图。但一开始时会先加载相机胶卷图片，并自动跳转到图片选择视图。

import UIKit
import Photos

//图片缩略图集合页控制器
class HGImageCollectionViewController: UIViewController {
    //用于显示所有图片缩略图的collectionView
    @IBOutlet weak var collectionView:UICollectionView!
    
    //下方工具栏
    @IBOutlet weak var toolBar:UIToolbar!

    //取得的资源结果，用了存放的PHAsset
    var assetsFetchResults:PHFetchResult<PHAsset>?
    
    //带缓存的图片管理对象
    var imageManager:PHCachingImageManager!
    
    //缩略图大小
    var assetGridThumbnailSize:CGSize!
    
    //每次最多可选择的照片数量
    var maxSelected:Int = Int.max
    
    //照片选择完毕后的回调
    var completeHandler:((_ assets:[PHAsset])->())?
    
    //完成按钮
    var completeButton:HGImageCompleteButton!
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        //根据单元格的尺寸计算我们需要的缩略图大小
        let scale = UIScreen.main.scale
        let cellSize = (self.collectionView.collectionViewLayout as!
            UICollectionViewFlowLayout).itemSize
        assetGridThumbnailSize = CGSize(width: cellSize.width*scale ,
                                        height: cellSize.height*scale)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        //背景色设置为白色（默认是黑色）
        self.collectionView.backgroundColor = UIColor.white
        
        //初始化和重置缓存
        self.imageManager = PHCachingImageManager()
        self.resetCachedAssets()
        
        //设置单元格尺寸
        let layout = (self.collectionView.collectionViewLayout as!
            UICollectionViewFlowLayout)
        layout.itemSize = CGSize(width: UIScreen.main.bounds.size.width/4-1,
                                 height: UIScreen.main.bounds.size.width/4-1)
        //允许多选
        self.collectionView.allowsMultipleSelection = true
        
        //添加导航栏右侧的取消按钮
        let rightBarItem = UIBarButtonItem(title: "取消", style: .plain,
                                           target: self, action: #selector(cancel))
        self.navigationItem.rightBarButtonItem = rightBarItem
      
        //添加下方工具栏的完成按钮
        completeButton = HGImageCompleteButton()
        completeButton.addTarget(target: self, action: #selector(finishSelect))
        completeButton.center = CGPoint(x: UIScreen.main.bounds.width - 50, y: 22)
        completeButton.isEnabled = false
        toolBar.addSubview(completeButton)
    }

    //重置缓存
    func resetCachedAssets(){
        self.imageManager.stopCachingImagesForAllAssets()
    }
    
    
    //取消按钮点击
    func cancel() {
        //退出当前视图控制器
        self.navigationController?.dismiss(animated: true, completion: nil)
    }
    
    //获取已选择个数
    func selectedCount() -> Int {
        return self.collectionView.indexPathsForSelectedItems?.count ?? 0
    }

    //完成按钮点击
    func finishSelect(){
        //取出已选择的图片资源
        var assets:[PHAsset] = []
        if let indexPaths = self.collectionView.indexPathsForSelectedItems{
            for indexPath in indexPaths{
                assets.append(assetsFetchResults![indexPath.row] )
            }
        }
        //调用回调函数
        self.navigationController?.dismiss(animated: true, completion: {
            self.completeHandler?(assets)
        })
    }
}

//图片缩略图集合页控制器UICollectionViewDataSource,UICollectionViewDelegate协议方法的实现
extension HGImageCollectionViewController:UICollectionViewDataSource
,UICollectionViewDelegate{
    //CollectionView项目
    func collectionView(_ collectionView: UICollectionView,
                        numberOfItemsInSection section: Int) -> Int {
        return self.assetsFetchResults?.count ?? 0
    }
    
    // 获取单元格
    func collectionView(_ collectionView: UICollectionView,
                        cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        //获取storyboard里设计的单元格，不需要再动态添加界面元素
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell",
                                    for: indexPath) as! HGImageCollectionViewCell
        let asset = self.assetsFetchResults![indexPath.row]
        //获取缩略图
        self.imageManager.requestImage(for: asset, targetSize: assetGridThumbnailSize,
                                       contentMode: .aspectFill, options: nil) {
                                        (image, nfo) in
            cell.imageView.image = image
        }
        
        return cell
    }
    
    //单元格选中响应
    func collectionView(_ collectionView: UICollectionView,
                        didSelectItemAt indexPath: IndexPath) {
        if let cell = collectionView.cellForItem(at: indexPath)
            as? HGImageCollectionViewCell{
            //获取选中的数量
            let count = self.selectedCount()
            //如果选择的个数大于最大选择数
            if count > self.maxSelected {
                //设置为不选中状态
                collectionView.deselectItem(at: indexPath, animated: false)
                //弹出提示
                let title = "你最多只能选择\(self.maxSelected)张照片"
                let alertController = UIAlertController(title: title, message: nil,
                                                        preferredStyle: .alert)
                
                let cancelAction = UIAlertAction(title:"我知道了", style: .cancel,
                                                 handler:nil)
                alertController.addAction(cancelAction)
                self.present(alertController, animated: true, completion: nil)
            }
            //如果不超过最大选择数
            else{
                //改变完成按钮数字，并播放动画
                completeButton.num = count
                if count > 0 && !self.completeButton.isEnabled{
                    completeButton.isEnabled = true
                }
                cell.playAnimate()
            }
        }
    }
    
    //单元格取消选中响应
    func collectionView(_ collectionView: UICollectionView,
                        didDeselectItemAt indexPath: IndexPath) {
        if let cell = collectionView.cellForItem(at: indexPath)
            as? HGImageCollectionViewCell{
             //获取选中的数量
            let count = self.selectedCount()
            completeButton.num = count
             //改变完成按钮数字，并播放动画
            if count == 0{
                completeButton.isEnabled = false
            }
            cell.playAnimate()
        }
    }
}

import UIKit

//图片缩略图集合页单元格
open class HGImageCollectionViewCell: UICollectionViewCell {
    //显示缩略图
    @IBOutlet weak var imageView:UIImageView!
    
    //显示选中状态的图标
    @IBOutlet weak var selectedIcon:UIImageView!
    
    //设置是否选中
    open override var isSelected: Bool {
        didSet{
            if isSelected {
                selectedIcon.image = UIImage(named: "hg_image_selected")
            }else{
                selectedIcon.image = UIImage(named: "hg_image_not_selected")
            }
        }
    }
    
    //播放动画，是否选中的图标改变时使用
    func playAnimate() {
        //图标先缩小，再放大
        UIView.animateKeyframes(withDuration: 0.4, delay: 0, options: .allowUserInteraction,
                                animations: {
            UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 0.2,
                               animations: {
                self.selectedIcon.transform = CGAffineTransform(scaleX: 0.7, y: 0.7)
            })
            UIView.addKeyframe(withRelativeStartTime: 0.2, relativeDuration: 0.4,
                               animations: {
                self.selectedIcon.transform = CGAffineTransform.identity
            })
            }, completion: nil)
    }
    
    open override func awakeFromNib() {
        super.awakeFromNib()
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
    }
}

import UIKit

//照片选择页下方工具栏的“完成”按钮
class HGImageCompleteButton: UIView {
    //已选照片数量标签
    var numLabel:UILabel!
    //按钮标题标签“完成”
    var titleLabel:UILabel!
    
    //按钮的默认尺寸
    let defaultFrame = CGRect(x:0, y:0, width:70, height:20)
    
    //文字颜色（同时也是数字背景颜色）
    let titleColor = UIColor(red: 0x09/255, green: 0xbb/255, blue: 0x07/255, alpha: 1)
    
    //点击点击手势
    var tapSingle:UITapGestureRecognizer?
    
    //设置数量
    var num:Int = 0{
        didSet{
            if num == 0{
                numLabel.isHidden = true
            }else{
                numLabel.isHidden = false
                numLabel.text = "\(num)"
                playAnimate()
            }
        }
    }
    
    //是否可用
    var isEnabled:Bool = true {
        didSet{
            if isEnabled {
                titleLabel.textColor = titleColor
                tapSingle?.isEnabled = true
            }else{
                titleLabel.textColor = UIColor.gray
                tapSingle?.isEnabled = false
            }
        }
    }
    
    init(){
        super.init(frame:defaultFrame)
    
        //已选照片数量标签初始化
        numLabel = UILabel(frame:CGRect(x: 0 , y: 0 , width: 20, height: 20))
        numLabel.backgroundColor = titleColor
        numLabel.layer.cornerRadius = 10
        numLabel.layer.masksToBounds = true
        numLabel.textAlignment = .center
        numLabel.font = UIFont.systemFont(ofSize: 15)
        numLabel.textColor = UIColor.white
        numLabel.isHidden = true
        self.addSubview(numLabel)
        
        //按钮标题标签初始化
        titleLabel = UILabel(frame:CGRect(x: 20 , y: 0 ,
                                          width: defaultFrame.width - 20,
                                          height: 20))
        titleLabel.text = "完成"
        titleLabel.textAlignment = .center
        titleLabel.font = UIFont.systemFont(ofSize: 15)
        titleLabel.textColor = titleColor
        self.addSubview(titleLabel)
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    //用户数字改变时播放的动画
    func playAnimate() {
        //从小变大，且有弹性效果
        self.numLabel.transform = CGAffineTransform(scaleX: 0.1, y: 0.1)
        UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.5,
                       initialSpringVelocity: 0.5, options: UIViewAnimationOptions(),
                       animations: {
            self.numLabel.transform = CGAffineTransform.identity
        }, completion: nil)
    }
    
    //添加事件响应
    func addTarget(target: Any?, action: Selector?) {
        //单击监听
        tapSingle = UITapGestureRecognizer(target:target,action:action)
        tapSingle!.numberOfTapsRequired = 1
        tapSingle!.numberOfTouchesRequired = 1
        self.addGestureRecognizer(tapSingle!)
    }
}

3，相关资源

• 在 storyboard 中添加两个 View Controller Scene，分别绑定上面的 HGImagePickerController 和 HGImageCollectionViewController。
• 同时两个 Scene 中的 cell 分别绑定 HGImagePickerCell 和 HGImageCollectionViewCell。
• Image Picker Controller Scene 的 Storyboard ID 设置为 imagePickerVC。单元格 identifier 设置为 cell。
• Image Collection View Controller Scene 的 Storyboard ID 设置为 hgImageCollectionVC。单元格 identifier 设置为 cell。
• 从 Image Picker Controller Scene 的单元格拖动一个 Segue 到 Image Collection View Controller Scene。类型为 Show，identifier 为 showImages。

三、使用样例

1，Info.plist配置

2，样例代码

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    //“开始选择照片”按钮点击
    @IBAction func buttonTapped(_ sender: AnyObject) {
        //开始选择照片，最多允许选择4张
        _ = self.presentHGImagePicker(maxSelected:4) { (assets) in
            //结果处理
            print("共选择了\(assets.count)张图片，分别如下：")
            for asset in assets {
                print(asset)
            }
        }
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}