SwiftUI 在滚动列表期间停止更新

Question

给定 SwiftUI 中的列表，一旦开始平移，列表中 View 的更新似乎会暂停，直到滚动停止。有没有办法防止这种情况？

考虑以下代码:

class Model: ObservableObject, Identifiable {
    @Published var offset: CGFloat = 0

    let id = UUID()
    private var timer: Timer!

    init() {
        timer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true, block: { _ in
            self.update()
        })
    }

    func update() {
        offset = CGFloat.random(in: 0...300)
    }
}

struct ContentView: View {
    @ObservedObject var model1 = Model()
    @ObservedObject var model2 = Model()
    @ObservedObject var model3 = Model()
    @ObservedObject var model4 = Model()

    var body: some View {
        List {
            ForEach([model1, model2, model3, model4]) {
                Rectangle()
                    .foregroundColor(.red)
                    .frame(width: $0.offset, height: 30, alignment: .center)
                    .animation(.default)
            }
        }
    }
}

将导致这种行为:

Answer 1

这是由于 Timer 的性质所致和 RunLoop .使用 GCD 代替，如下面的方法

init() {
    var runner: (() -> ())?
    runner = {
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { [weak self] in
            if let self = self {
                self.update()
                runner?()
            }
        }
    }
    runner?()
}