WWDC20-10652-认识新照片选择器

Monday. August 16, 2021 - 7 mins

让人们选择在您的应用程序中使用的照片和视频，而无需完全访问照片库。了解适用于iOS和Mac Catalyst的PHPicker API如何确保隐私，同时为您的应用程序提供您所需的功能。

PHPicker是UIImagePickerController的现代替代品。除了以隐私为重点的方法外，API还为您的应用程序提供了其他功能，如搜索、多图像选择以及在照片网格上放大或缩小的能力。我们将向您展示PHPicker如何帮助大多数应用程序避免要求直接访问库，以及如何实现它，以改善与您的应用程序交互的人的整体体验。

介绍PHPicker
API说明
Demo:

介绍PHPicker

PHPicker：一个新的系统提供的选择器，允许您从用户的照片库中访问照片和视频。

建议您使用此选择器，而不是构建自己的自定义照片选择用户界面。

新版本包括：

访问“照片”中照片和视频数据的最好方式
全新设计
新的易用API
支持多项选择
缩放手势
指定可选择类型

PHPicker默认内置隐私保护：

独立进程，通过XPC与应用程序对话，屏幕不能截屏
只有用户选择的内容才会被传回宿主App
您的应用程序不会直接访问照片库
它不需要获得照片库权限（除非你真的需要，否则不要要求它）

PHPicker不是单个类的名称，而是一组一起工作的类。

API说明

PHPickerConfiguration– 允许您指定限制和过滤器：

selectionLimit–可以选择的项目数量（1默认，0 = 无限）
filter – e.g. .images or .any(of: [.videos, .livePhotos])

PHPickerViewController– 处理选择器的主视图控制器：

the picker doesn’t dismiss itself automatically, call picker.dismiss(animated:) when you get the response

PHPickerViewControllerDelegate– 挑选者的代表：

picker(_: didFinishPicking results:)

PHPickerResult– 这些对象的数组作为响应传递给应用程序

从结果中获取 itemProvider
检查itemProvider.canLoadObject(ofClass: UIImage.self)
通过itemProvider.loadObject(ofClass: UIImage.self) { … }

您通常可以从PHPickerResult中提取照片，而无需访问PHPhotoLibrary，但如果您确实需要访问照片库，请将其传递给PHPickerConfiguration.init，并从选择器结果中获取assetIdentifier引用。

如果您使用具有照片库访问权限的PHPicker，并且您只能有限地访问照片子集，那么：

PHPicker仍然允许用户从整个库中选择照片
但您可以直接访问的选择不会因他们在选择器中选择的内容而扩展

不建议使用UIImagePickerController的照片库API。

Demo:

使用PHPickerConfiguration

import PhotosUI

var configuration = PHPickerConfiguration()

// “unlimited” selection by specifying 0, default is 1
configuration.selectionLimit = 0

// Only show images (including Live Photos)
configuration.filter = .images
// Uncomment next line for other example: Only show videos or Live Photos (for their video complement), but no images
// configuration.filter = .any(of: [.videos, .livePhotos])

使用PHPickerViewController

import UIKit
import PhotosUI

class SingleSelectionPickerViewController: UIViewController, PHPickerViewControllerDelegate {
    @IBAction func presentPicker(_ sender: Any) {
        var configuration = PHPickerConfiguration()
        // Only wants images
        configuration.filter = .images
        
        let picker = PHPickerViewController(configuration: configuration)
        picker.delegate = self
        
        // The client is responsible for presentation and dismissal
        present(picker, animated: true)
    }
    
    func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        // The client is responsible for presentation and dismissal
        picker.dismiss(animated: true)
        
        // Get the first item provider from the results, the configuration only allowed one image to be selected
        let itemProvider = results.first?.itemProvider
        
        if let itemProvider = itemProvider, itemProvider.canLoadObject(ofClass: UIImage.self) {
            itemProvider.loadObject(ofClass: UIImage.self) { (image, error) in
                // TODO: Do something with the image or handle the error
            }
        } else {
            // TODO: Handle empty results or item provider not being able load UIImage
        }
    }
}

使用单选

import UIKit
import PhotosUI

class ViewController: UIViewController {
    
    @IBOutlet weak var imageView: UIImageView!
    
    @IBAction func presentPicker(_ sender: Any) {
        var configuration = PHPickerConfiguration()
        configuration.filter = .images
        
        let picker = PHPickerViewController(configuration: configuration)
        picker.delegate = self
        present(picker, animated: true)
    }
    
}

extension ViewController: PHPickerViewControllerDelegate {
    
    func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        dismiss(animated: true)
        
        if let itemProvider = results.first?.itemProvider, itemProvider.canLoadObject(ofClass: UIImage.self) {
            let previousImage = imageView.image
            itemProvider.loadObject(ofClass: UIImage.self) { [weak self] image, error in
                DispatchQueue.main.async {
                    guard let self = self, let image = image as? UIImage, self.imageView.image == previousImage else { return }
                    self.imageView.image = image
                }
            }
        }
    }
    
}

使用多选

import UIKit
import PhotosUI

class ViewController: UIViewController {
    
    @IBOutlet weak var imageView: UIImageView!
    
    var itemProviders: [NSItemProvider] = []
    var iterator: IndexingIterator<[NSItemProvider]>?
    
    @IBAction func presentPicker(_ sender: Any) {
        var configuration = PHPickerConfiguration()
        configuration.filter = .images
        configuration.selectionLimit = 0
        
        let picker = PHPickerViewController(configuration: configuration)
        picker.delegate = self
        present(picker, animated: true)
    }
    
    func displayNextImage() {
        if let itemProvider = iterator?.next(), itemProvider.canLoadObject(ofClass: UIImage.self) {
            let previousImage = imageView.image
            itemProvider.loadObject(ofClass: UIImage.self) { [weak self] image, error in
                DispatchQueue.main.async {
                    guard let self = self, let image = image as? UIImage, self.imageView.image == previousImage else { return }
                    self.imageView.image = image
                }
            }
        }
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        displayNextImage()
    }
    
}

extension ViewController: PHPickerViewControllerDelegate {
    
    func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        dismiss(animated: true)
        
        itemProviders = results.map(\.itemProvider)
        iterator = itemProviders.makeIterator()
        displayNextImage()
    }
    
}

PHPicker 和 PhotoKit 配合使用

import UIKit
import PhotosUI

class PhotoKitPickerViewController: UIViewController, PHPickerViewControllerDelegate {
    @IBAction func presentPicker(_ sender: Any) {
        let photoLibrary = PHPhotoLibrary.shared()
        let configuration = PHPickerConfiguration(photoLibrary: photoLibrary)
        let picker = PHPickerViewController(configuration: configuration)
        picker.delegate = self
        present(picker, animated: true)
    }
    
    func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        picker.dismiss(animated: true)
        
        let identifiers = results.compactMap(\.assetIdentifier)
        let fetchResult = PHAsset.fetchAssets(withLocalIdentifiers: identifiers, options: nil)
        
        // TODO: Do something with the fetch result if you have Photos Library access
    }
}