我正在尝试重写我的图像缓存以摆脱对 Alamofire 的使用,但这样做时我遇到了错误。以前,我的图像缓存代码是:
let imageCache = NSCache<NSString, UIImage>()
extension UIImageView {
func loadImageUsingCacheWithUrlString(_ urlString: String) {
self.image = nil
// Check cache for image first
if let cachedImage = imageCache.object(forKey: urlString as NSString) {
self.image = cachedImage
return
}
// Otherwise fire off a new download
Alamofire.request(urlString)
.responseImage { response in
if let downloadedImage = response.result.value {
// image is here.
imageCache.setObject(downloadedImage, forKey: urlString as NSString)
self.image = downloadedImage
}
}
}
}
使用示例如下:
navBarCell.avatarImageView.loadImageUsingCacheWithUrlString(avatars[indexPath.row])
现在我重写了缓存:
class ImageService {
static let cache = NSCache<NSString, UIImage>()
static func downloadImage(url: URL, completion: @escaping (_ image: UIImage?) -> (Void)) {
URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else {return}
var downloadedImage: UIImage?
downloadedImage = UIImage(data: data)
if downloadedImage != nil {
cache.setObject(downloadedImage!, forKey: url.absoluteString as NSString)
}
DispatchQueue.main.async {
completion(downloadedImage)
}
}.resume()
}
static func getImage(url: URL, completion: @escaping (_ image: UIImage?) -> (Void)) {
if let image = cache.object(forKey: url.absoluteString as NSString) {
completion(image)
} else {
downloadImage(url: url, completion: completion)
}
}
}
并在与上述相同的场景中使用它:
if let avatarImageUrlString = self.chatVC?.avatarDictionary.allValues as! [String], let imageUrl = URL(string: avatarImageUrlString) {
ImageService.getImage(url: imageUrl, completion: { (image) -> (Void) in
navBarCell.avatarImageView.image = image
})
}
我在 if let
语句中收到错误 Initializer for conditional binding must have Optional type, not '[String]'
。
我不确定如何处理这个 - 我需要 [String]
数组,但如果我正确理解错误,它需要是一个可选的,而不是用 强制解包作为! [字符串]
?如果这是一个新手问题,我深表歉意,但我似乎无法让它发挥作用。
感谢您的指导!
编辑:
我试过将 let avatarImageUrlString....
放在 if let
之外:
let avatarImageUrlString = self.chatVC?.avatarDictionary.allValues as! [String]
if let imageUrl = URL(string: avatarImageUrlString) {
ImageService.getImage(url: imageUrl, completion: { (image) -> (Void) in
navBarCell.avatarImageView.image = image
})
}
但是在 if let
行出现错误 Cannot convert value of type '[String]' to expected argument type 'String'
。
我也试过删除 !
并且我收到错误消息 '[Any]?'不可转换为“[String]”;你是不是想用 'as!'强制向下转换?
修复建议将 !
放回:将 'as' 替换为 'as!'
编辑 2:
if let avatarImageUrlString = self.chatVC?.avatarDictionary.allValues as? [String], let imageUrl = URL(string: avatarImageUrlString[0]) {
ImageService.getImage(url: imageUrl, completion: { (image) -> (Void) in
navBarCell.avatarImageView.image = image
})
}
编辑 3:
let avatars = self.chatVC?.avatarDictionary.allValues[indexPath.row] as? [String]
if let avatarImageUrlString = avatars, let imageUrl = URL(string: avatarImageUrlString[0]) {
ImageService.getImage(url: imageUrl, completion: { (image) -> (Void) in
navBarCell.avatarImageView.image = image
})
}
最佳答案
您实际上是将 allValues
强制解包为 [String]
,因此没有什么可沮丧的。还将类型从字符串数组更改为单个字符串
所以在可选绑定(bind)中不用这个
as! [String]
用这个
as? String
所以...
if let avatarImageUrlString = self.chatVC?.avatarDictionary.allValues[indexPath.row] as? String, let imageUrl = URL(string: avatarImageUrlString) {
...
}
关于ios - 使用图像缓存时展开 [String] 的问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53711336/