如何通过UIKit实现类似Photos app的图片选择器

要实现类似Photos app的图片选择器，可以通过使用UIImagePickerController类以及UICollectionView来实现。下面是一个简单的示例代码：

1. 创建一个按钮，点击按钮后打开图片选择器：

import UIKit

class ViewController: UIViewController, UIImagePickerControllerDelegate & UINavigationControllerDelegate {
    
    let imagePicker = UIImagePickerController()

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let button = UIButton(frame: CGRect(x: 100, y: 100, width: 200, height: 50))
        button.setTitle("Select Image", for: .normal)
        button.addTarget(self, action: #selector(selectImage), for: .touchUpInside)
        view.addSubview(button)
        
        imagePicker.delegate = self
        imagePicker.allowsEditing = false
        imagePicker.sourceType = .photoLibrary
    }
    
    @objc func selectImage() {
        present(imagePicker, animated: true, completion: nil)
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        if let image = info[.originalImage] as? UIImage {
            //处理选中的图片
        }
        
        dismiss(animated: true, completion: nil)
    }
    
    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        dismiss(animated: true, completion: nil)
    }
}

2. 创建一个UICollectionView来展示选择的图片：

class ImageCollectionViewController: UICollectionViewController {
    
    var selectedImages: [UIImage] = []
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return selectedImages.count
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCell", for: indexPath) as! ImageCell
        cell.imageView.image = selectedImages[indexPath.row]
        return cell
    }
}

class ImageCell: UICollectionViewCell {
    
    let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        contentView.addSubview(imageView)
    }
}

通过以上代码，你可以实现一个简单的图片选择器，并用UICollectionView展示选中的图片。你可以根据需求进一步自定义UI和功能。