试试这个:

import SwiftUI

struct LoadingPlaceholder: View {
    var text = "Loading..."
    init(text:String ) {
        self.text = text
    }
    var body: some View {
        VStack(content: {
            ProgressView(self.text)
        })
    }
}

更多关于SwiftUI ProgressView的信息

// Activity View

struct ActivityIndicator: UIViewRepresentable {

    let style: UIActivityIndicatorView.Style
    @Binding var animate: Bool

    private let spinner: UIActivityIndicatorView = {
        $0.hidesWhenStopped = true
        return $0
    }(UIActivityIndicatorView(style: .medium))

    func makeUIView(context: UIViewRepresentableContext<ActivityIndicator>) -> UIActivityIndicatorView {
        spinner.style = style
        return spinner
    }

    func updateUIView(_ uiView: UIActivityIndicatorView, context: UIViewRepresentableContext<ActivityIndicator>) {
        animate ? uiView.startAnimating() : uiView.stopAnimating()
    }

    func configure(_ indicator: (UIActivityIndicatorView) -> Void) -> some View {
        indicator(spinner)
        return self
    }   
}

// Usage
struct ContentView: View {

    @State var animate = false

    var body: some View {
            ActivityIndicator(style: .large, animate: $animate)
                .configure {
                    $0.color = .red
            }
            .background(Color.blue)
    }
}

从Xcode 12 beta版(iOS 14)开始，开发者可以使用一个名为ProgressView的新视图，它可以显示确定进度和不确定进度。

它的样式默认为CircularProgressViewStyle，这正是我们正在寻找的。

var body: some View {
    VStack {
        ProgressView()
           // and if you want to be explicit / future-proof...
           // .progressViewStyle(CircularProgressViewStyle())
    }
}

Xcode 11.倍

相当多的视图还没有在SwiftUI中表示，但很容易将它们移植到系统中。 你需要包装UIActivityIndicator并使其UIViewRepresentable。

(关于这方面的更多信息，可以在WWDC 2019的精彩演讲-集成SwiftUI中找到)

struct ActivityIndicator: UIViewRepresentable {

    @Binding var isAnimating: Bool
    let style: UIActivityIndicatorView.Style

    func makeUIView(context: UIViewRepresentableContext<ActivityIndicator>) -> UIActivityIndicatorView {
        return UIActivityIndicatorView(style: style)
    }

    func updateUIView(_ uiView: UIActivityIndicatorView, context: UIViewRepresentableContext<ActivityIndicator>) {
        isAnimating ? uiView.startAnimating() : uiView.stopAnimating()
    }
}

然后你可以使用它如下-这是一个加载叠加的例子。

注意:我更喜欢使用ZStack，而不是overlay(:_)，所以我确切地知道在我的实现中发生了什么。

struct LoadingView<Content>: View where Content: View {

    @Binding var isShowing: Bool
    var content: () -> Content

    var body: some View {
        GeometryReader { geometry in
            ZStack(alignment: .center) {

                self.content()
                    .disabled(self.isShowing)
                    .blur(radius: self.isShowing ? 3 : 0)

                VStack {
                    Text("Loading...")
                    ActivityIndicator(isAnimating: .constant(true), style: .large)
                }
                .frame(width: geometry.size.width / 2,
                       height: geometry.size.height / 5)
                .background(Color.secondary.colorInvert())
                .foregroundColor(Color.primary)
                .cornerRadius(20)
                .opacity(self.isShowing ? 1 : 0)

            }
        }
    }

}

要测试它，你可以使用下面的示例代码:

struct ContentView: View {

    var body: some View {
        LoadingView(isShowing: .constant(true)) {
            NavigationView {
                List(["1", "2", "3", "4", "5"], id: \.self) { row in
                    Text(row)
                }.navigationBarTitle(Text("A List"), displayMode: .large)
            }
        }
    }

}

结果:

基本活动指标结果:

试试这个:

import SwiftUI

struct LoadingPlaceholder: View {
    var text = "Loading..."
    init(text:String ) {
        self.text = text
    }
    var body: some View {
        VStack(content: {
            ProgressView(self.text)
        })
    }
}

更多关于SwiftUI ProgressView的信息

我已经使用AppKit和SwiftUI修改了Matteo Pacini的macOS答案。这允许你在SwiftUI中使用NSProgressIndicator，同时保留macOS 10.15的功能。

import AppKit
import SwiftUI

struct ActivityIndicator: NSViewRepresentable {
    
    @Binding var isAnimating: Bool
    let style: NSProgressIndicator.Style

    func makeNSView(context: NSViewRepresentableContext<ActivityIndicator>) -> NSProgressIndicator {
        let progressIndicator = NSProgressIndicator()
        progressIndicator.style = self.style
        return progressIndicator
    }

    func updateNSView(_ nsView: NSProgressIndicator, context: NSViewRepresentableContext<ActivityIndicator>) {
        isAnimating ? nsView.startAnimation(nil) : nsView.stopAnimation(nil)
    }
    
}

用法如下:

ActivityIndicator(isAnimating: .constant(true), style: .spinning)