Photos框架详解 ---- PHImageManager

摘自Mattt Thompson 的PHImage​Manager

1、tableView 中使用 PHImageManager加载图片

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath)

    let manager = PHImageManager.defaultManager()

    if cell.tag != 0 {
        manager.cancelImageRequest(PHImageRequestID(cell.tag))
    }

    let asset = assets[indexPath.row]

    if let creationDate = asset.creationDate {
        cell.textLabel?.text = NSDateFormatter.localizedStringFromDate(creationDate,
            dateStyle: .MediumStyle,
            timeStyle: .MediumStyle
        )
    } else {
        cell.textLabel?.text = nil
    }

    cell.tag = Int(manager.requestImageForAsset(asset,
        targetSize: CGSize(width: 100.0, height: 100.0),
        contentMode: .AspectFill,
        options: nil) { (result, _) in
            if let destinationCell = tableView.cellForRowAtIndexPath(indexPath) {
                destinationCell.imageView?.image = result
            }
    })

    return cell
}

2、PHCachingImageManager 缓存需要显示的图片 with Swift 的willSet / didSet hooks

let cachingImageManager = PHCachingImageManager()
var assets: [PHAsset] = [] {
    willSet {
        cachingImageManager.stopCachingImagesForAllAssets()
    }

    didSet {
        cachingImageManager.startCachingImagesForAssets(self.assets,
            targetSize: PHImageManagerMaximumSize,
            contentMode: .AspectFit,
            options: nil
        )
    }
}

3、使用 PHImageManager 和 PHImageRequestOptions 的复杂功能来做人脸识别

let asset: PHAsset

@IBOutlet weak var imageView: UIImageView!
@IBOutlet weak var progressView: UIProgressView!

override func viewDidLoad() {
    super.viewDidLoad()

    let manager = PHImageManager.defaultManager()

    let initialRequestOptions = PHImageRequestOptions()
    initialRequestOptions.synchronous = true
    initialRequestOptions.resizeMode = .Fast
    initialRequestOptions.deliveryMode = .FastFormat

    manager.requestImageForAsset(asset,
        targetSize: CGSize(width: 250.0, height: 250.0),
        contentMode: .AspectFit,
        options: initialRequestOptions) { (initialResult, _) in
            guard let ciImage = initialResult?.CIImage else {
                return
            }

            let finalRequestOptions = PHImageRequestOptions()
            finalRequestOptions.progressHandler = { (progress, _, _, _) in
                self.progressView.progress = Float(progress)
            }

            let detector = CIDetector(
                ofType: CIDetectorTypeFace,
                context: nil,
                options: [CIDetectorAccuracy: CIDetectorAccuracyLow]
            )

            let features = detector.featuresInImage(ciImage)
            if features.count > 0 {
                var rect = CGRectZero
                features.forEach {
                    rect.unionInPlace($0.bounds)
                }

                let transform = CGAffineTransformMakeScale(1.0 / initialResult!.size.width, 1.0 / initialResult!.size.height)
                finalRequestOptions.normalizedCropRect = CGRectApplyAffineTransform(rect, transform)
            }

            manager.requestImageForAsset(self.asset,
                targetSize: PHImageManagerMaximumSize,
                contentMode: .AspectFit,
                options: finalRequestOptions) { (finalResult, _) in
                    self.imageView.image = finalResult
            }
    }
}