import UIKit 
import Photos //使用圖庫功能時必須引用這個包 
//顯示最近拍攝的照片為縮略圖 
class ViewController: UIViewController, PHPhotoLibraryChangeObserver { 
 var assetsFetchResults:PHFetchResult<PHAsset>! 
 var imageManager: PHCachingImageManager! //帶緩存的圖片管理對象 
 var imageView: UIImageView! //用于顯示縮略圖 
 var assetGridThumbnailSize: CGSize! //縮略圖大小 
 override func viewDidLoad() { 
  super.viewDidLoad() 
  // Do any additional setup after loading the view, typically from a nib. 
  imageView = UIImageView() 
  imageView.frame = CGRect(x: 50, y: 50, width: 100, height: 100) 
  imageView.contentMode = .scaleAspectFit 
  imageView.clipsToBounds = true 
  self.view.addSubview(imageView) 
  self.imageManager = PHCachingImageManager() //初始化和充值緩存 
  let scale = UIScreen.main.scale //像素比 
  assetGridThumbnailSize = CGSize(width: imageView.frame.width*scale, 
          height: imageView.frame.height*scale) 
  //申請權限 
  PHPhotoLibrary.requestAuthorization({ (status) in 
   if status != .authorized { 
    return 
   } 
   //獲取所有圖片資源(按照創建時間排序) 
   let allPhotoOptions = PHFetchOptions() 
   allPhotoOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", 
                ascending: false)] //排序方式 
   allPhotoOptions.predicate = NSPredicate(format: "mediaType = %d", 
             PHAssetMediaType.image.rawValue) //類型 
   self.assetsFetchResults = PHAsset.fetchAssets(with: .image, 
               options: allPhotoOptions) //查詢照片類型 
   var i = 0 
   while i<self.assetsFetchResults.count { 
    let asset = self.assetsFetchResults[i] 
    print(" 創建時間：\(asset.creationDate?.description)") //打印所有圖片的創建時間 
    i += 1 
   } 
   if (self.assetsFetchResults.count > 0) { 
    //顯示最近一張拍攝的圖片（也可以根據拍攝時間遠近決定是否要顯示） 
    self.imageManager.requestImage(for: self.assetsFetchResults[0],  //最近一張圖片 
            targetSize: self.assetGridThumbnailSize, 
            contentMode: .aspectFill, 
            options: nil, resultHandler: { (image, info) in 
            self.imageView.image = image //取出圖像并顯示出來 
    }) 
   } 
   print("圖片數量：\(self.assetsFetchResults?.count)") 
   //注冊監聽資源變化 
   PHPhotoLibrary.shared().register(self) //刪除是unregisterChangeObserver 
  }) 
 } 
 override func didReceiveMemoryWarning() { 
  super.didReceiveMemoryWarning() 
  // Dispose of any resources that can be recreated. 
 } 
 func photoLibraryDidChange(_ changeInstance: PHChange) { 
  guard let changes = changeInstance.changeDetails(for: self.assetsFetchResults as! PHFetchResult<PHObject>) else { 
   return 
  } 
  //異步執行，避免阻塞圖片變化事件隊列 
  DispatchQueue.main.async { 
   if let result = changes.fetchResultAfterChanges as? PHFetchResult<PHAsset> { 
    self.assetsFetchResults = result //差異結果 
   } 
   //判斷是否有新增圖片或刪除圖片的情況 
   if !changes.hasIncrementalChanges || changes.hasMoves { 
    return 
   } else { 
    print("圖片數據有變化") 
    if let indexs = changes.changedIndexes, indexs.count>0 { //不顯示0的情況 
     print("有\(indexs.count)張圖片發生變化") 
    } 
    if let removes = changes.removedIndexes, removes.count>0 { 
     print("刪除了\(removes.count)張圖片") 
    } 
    if let inserts = changes.insertedIndexes, inserts.count>0 { 
     //有新增圖片 
     print("新增了\(inserts.count)張圖片") 
     let picture = self.assetsFetchResults[inserts.first!] 
     self.imageManager.requestImage(for: picture, 
             targetSize: self.assetGridThumbnailSize, 
             contentMode: .aspectFill, 
             options: nil, resultHandler: { (image, option) in 
             self.imageView.image = image //取出圖像并顯示出來 
     }) 
    } 
   } 
  } 
 } 
}