在SwiftUI
应用中,我的代码是这样的:
var body: some View {
VStack {
Spacer()
........
}
.onAppear {
.... I want to have some code here ....
.... to run when the view appears ....
}
}
我的问题是我想在 .onAppear 块中运行一些代码,以便在应用显示在屏幕上,启动后或在后台运行一段时间后可以运行它。但似乎这段代码在应用程序启动时仅运行一次,以后再也不会运行。我想念什么吗?还是应该使用其他策略来获得想要的结果?
答案 0 :(得分:4)
您必须在应用程序进入前台时观察该事件,然后使用@Published
将其发布到ContentView
。方法如下:
struct ContentView: View {
@ObservedObject var observer = Observer()
var body: some View {
VStack {
Spacer()
//...
}
.onReceive(self.observer.$enteredForeground) { _ in
print("App entered foreground!") // do stuff here
}
}
}
class Observer: ObservableObject {
@Published var enteredForeground = true
init() {
if #available(iOS 13.0, *) {
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIScene.willEnterForegroundNotification, object: nil)
} else {
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
}
@objc func willEnterForeground() {
enteredForeground.toggle()
}
}
答案 1 :(得分:4)
如果您针对 iOS14 进行链接,那么您可以利用新的 scenePhase
概念:
@Environment(\.scenePhase) var scenePhase
如果注入此属性,您可以针对以下三种条件进行测试:
switch newPhase {
case .inactive:
print("inactive")
case .active:
print("active")
case .background:
print("background")
}
所以,一起来:
struct ContentView: View {
@Environment(\.scenePhase) var scenePhase
var body: some View {
Text("Hello, World!")
.onChange(of: scenePhase) { newPhase in
switch newPhase {
case .inactive:
print("inactive")
case .active:
print("active")
case .background:
print("background")
}
}
}
}