Swift 3 NSCache 通用参数“KeyType”无法推断

的文章：

swift
import UIKit
// 创建一个全局的NSCache对象
let imageCache = NSCache()
// 加载图片的方法
func loadImage(withUrl urlString: String, completion: @escaping (UIImage?) -> Void) {
    // 先检查缓存中是否存在图片
    if let cachedImage = imageCache.object(forKey: urlString as NSString) {
        completion(cachedImage)
        return
    }
    
    // 如果缓存中不存在图片，则从网络上下载图片
    if let url = URL(string: urlString) {
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let data = data else {
                completion(nil)
                return
            }
            
            if let downloadedImage = UIImage(data: data) {
                // 将下载的图片存入缓存中
                imageCache.setObject(downloadedImage, forKey: urlString as NSString)
                completion(downloadedImage)
            } else {
                completion(nil)
            }
        }.resume()
    } else {
        completion(nil)
    }
}
// 使用示例
let imageUrl = "https://example.com/image.jpg"
loadImage(withUrl: imageUrl) { (image) in
    if let image = image {
        // 成功加载图片
        print("成功加载图片")
        // 在UI中显示图片
        DispatchQueue.main.async {
            // 更新UI
        }
    } else {
        // 加载图片失败
        print("加载图片失败")
    }
}

swift
let cache = NSCache()

swift
let cache = NSCache()

swift
let cache = NSCache()
// 缓存一个自定义对象
let key = "customObject" as AnyObject
let value = CustomObject() as AnyObject
cache.setObject(value, forKey: key)
// 获取缓存值时进行类型转换
if let cachedValue = cache.object(forKey: key) as? CustomObject {
    // 成功获取缓存值
    print("成功获取缓存值")
} else {
    // 获取缓存值失败
    print("获取缓存值失败")
}