SwiftUI点击切换远程加载图片时视图不刷新问题解决

@StateObject 的实例和视图生命周期绑定，仅会在视图首次创建时初始化一次。原有实现中Loader的网络请求逻辑写在初始化方法里，后续父视图刷新、传入的图片URL变更时，已经创建的Loader实例不会重新执行拉取逻辑，因此点击切换索引后图片不会更新。

TestView 层逻辑不需要调整，仅修改RemoteImage实现即可，修改后完整代码如下：

struct RemoteImage: View {
    private enum LoadState {
        case loading, success, failure
    }
    
    private class Loader: ObservableObject {
        var data = Data()
        var state = LoadState.loading
        
        func load(from url: String) {
            // 重置加载状态
            state = .loading
            data = Data()
            
            guard let parsedURL = URL(string: url) else {
                state = .failure
                DispatchQueue.main.async {
                    self.objectWillChange.send()
                }
                return
            }
            
            URLSession.shared.dataTask(with: parsedURL) { data, response, error in
                if let data = data, data.count > 0 {
                    self.data = data
                    self.state = .success
                } else {
                    self.state = .failure
                }
                
                DispatchQueue.main.async {
                    self.objectWillChange.send()
                }
            }.resume()
        }
    }
    
    private let url: String
    @StateObject private var loader = Loader()
    private var loading: Image
    private var failure: Image
    
    var body: some View {
        selectImage()
            .resizable()
            .onAppear {
                loader.load(from: url)
            }
            .onChange(of: url) { newUrl in
                loader.load(from: newUrl)
            }
    }
    
    init(url: String, loading: Image = Image(""), failure: Image = Image(systemName: "multiply.circle")) {
        self.url = url
        self.loading = loading
        self.failure = failure
    }
    
    private func selectImage() -> Image {
        switch loader.state {
        case .loading:
            return loading
        case .failure:
            return failure
        default:
            if let image = UIImage(data: loader.data) {
                return Image(uiImage: image)
            } else {
                return failure
            }
        }
    }
}

• 将Loader中原本写在初始化方法里的网络请求逻辑抽离为独立的load(from:)方法，支持重复调用加载不同地址的图片
• 移除init中对@StateObject的自定义初始化逻辑，避免StateObject实例生命周期和视图初始化强绑定导致的不更新问题
• 新增onChange(of: url)修饰符，监听父视图传入的URL变化，URL更新时主动触发新的图片加载请求
• 保留onAppear触发首次加载，保证视图首次展示时的正常拉取逻辑

内容的提问来源于stack exchange，提问作者nickcoding2