观察自定义视图 SwiftUI 中的属性变化

Question

我创建了一个自定义视图 NetworkImage，用于异步加载图像。

import Combine
import SwiftUI

struct NetworkImage<Placeholder: View>: View {
    @StateObject private var viewModel = NetworkImageViewModel()
    let url: String?
    let placeholder: Placeholder
    let saveLocally:Bool
    
    init(_ url: String?, @ViewBuilder placeholder: () -> Placeholder, saveLocally:Bool = false) {
        self.url = url
        self.placeholder = placeholder()
        self.saveLocally = saveLocally
    }
    
    func loadImage(_ url:String?)  {
        if let url = url {
            viewModel.loadImage(from: url, saveLocally: saveLocally)
        }
    }
    
    var body: some View {
        Group {
            if let uiImage = viewModel.image {
                Image(uiImage: uiImage)
                    .resizable()
            } else {
                placeholder
            }
        }
        .onAppear {
            if let url = url {
                viewModel.loadImage(from: url, saveLocally: saveLocally)
            }
        }
    }
}

我在我的观点中使用了它，它工作得非常好。但是现在我希望能够在每次 url 更改时用新图像替换图像。 我怎样才能做到这一点？如何将我的视图视图模型的 @Published 属性传递给此 NetworkImage 视图并使其工作？

谢谢

Answer 1

使用onChange修饰符查看url参数是否发生了变化：

struct NetworkImage<Placeholder: View>: View {
    @StateObject private var viewModel = NetworkImageViewModel()
    let url: String?
    let placeholder: Placeholder
    let saveLocally:Bool = false
    
    func loadImage(_ url:String?)  {
        if let url = url {
            viewModel.loadImage(from: url, saveLocally: saveLocally)
        }
    }
    
    var body: some View {
        Group {
            if let uiImage = viewModel.image {
                Image(uiImage: uiImage)
                    .resizable()
            } else {
                placeholder
            }
        }
        .onAppear {
            self.loadImage(url)
        }
        .onChange(of: url) { url in
            self.loadImage(url)
        }
    }
}