ios - DispatchQueue.main.async 阻塞主线程

Question

我一直在尝试在 Swift 3.0 中创建一个照片库，我想将存储在文档目录中的图像异步加载到 Collection View 中。我尝试了 DispatchQueue.main.async 但它阻塞了主线程并卡住了应用程序几秒钟:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let identifier = "ImageCell"
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath) as! ImageCell
    let url = self.imageURL[indexPath.row]
    cell.lazyLoadImage(from: url)
    return cell
}

和 ImageCell 类:

class ImageCell: UICollectionViewCell {
    @IBOutlet weak var imageView: UIImageView!

    func lazyLoadImage(from url: URL) {
        DispatchQueue.main.async {
            if let image = UIImage(contentsOfFile: url.path) {
                self.imageView.image = image
            }
        }
    }
}

感谢您的帮助。谢谢。

Answer 1

先切换到后台线程加载图片，再切换到主线程显示图片。

func lazyLoadImage(from url: URL) {
     DispatchQueue.global(qos: .userInteractive).async {
         if let image = UIImage(contentsOfFile: url.path) {
             DispatchQueue.main.async {
                 self.imageView.image = image
             }
         }
    }
}