问题描述
不知道我是否在滥用环境对象的想法,但在使用发布延迟异步值的环境对象时遇到问题。一个视图导航到下一个视图,但随后“根”被更新,结果导致“回声”,或者即使处理了导航问题。当使用导航之间的转换时,这个问题变得更加明显。 是否有正确的使用模式来避免这种情况?或者其他一些解决方案?
任何指导将不胜感激。
附上一个浓缩样本来说明问题。
Xcode 12.4 ios 14.1
final class SetColor: ObservableObject {
@Published var asyncVal: Bool = false
func flipIt() {
dispatchQueue.main.asyncAfter(deadline: .Now()+0.5,execute: {self.asyncVal.toggle()})
}
}
struct HomeView: View {
@StateObject var setCol: SetColor = SetColor()
@State private var navActive: Bool = false
var body: some View {
NavigationView {
ZStack {
Color(setCol.asyncVal ? .blue : .purple)
Button(action: {
setCol.flipIt()
navActive.toggle()
},label: {
Text("Change and Move")
})
.navigationTitle("Home")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
NavigationLink(destination: NavChild1().environmentObject(setCol),isActive: $navActive,label: { Text("GoTo 1 >") })
}
}
}
}
}
}
struct NavChild1: View {
@EnvironmentObject var setCol: SetColor
@State private var navActive: Bool = false
var body: some View {
ZStack {
Color(setCol.asyncVal ? .yellow : .orange)
Button(action: {
setCol.flipIt()
navActive.toggle()
},label: {
Text("Change and Move")
})
.navigationTitle("Nav 1")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
NavigationLink(destination: NavChild2().environmentObject(setCol),label: { Text("GoTo 2 >") })
}
}
}
}
}
struct NavChild2: View {
@EnvironmentObject var setCol: SetColor
@State private var navActive: Bool = false
var body: some View {
ZStack {
Color(setCol.asyncVal ? .yellow : .orange)
Button(action: {
setCol.flipIt()
navActive.toggle()
},label: {
Text("Change and Move")
})
.navigationTitle("Nav 2")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
NavigationLink(destination: NavChild3().environmentObject(setCol),label: { Text("GoTo 3 >") })
}
}
}
}
}
struct NavChild3: View {
@EnvironmentObject var setCol: SetColor
@State private var navActive: Bool = false
var body: some View {
ZStack {
Color(setCol.asyncVal ? .yellow : .orange)
Button(action: {
setCol.flipIt()
navActive.toggle()
},label: {
Text("Change and Move")
})
.navigationTitle("Nav 3")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
NavigationLink(destination: NavChild3().environmentObject(setCol),isActive: .constant(false),label: { Text("Go Home") })
}
}
}
}
}
struct HomeView_Previews: PreviewProvider {
static var previews: some View {
HomeView()
}
}
解决方法
您不需要在 GCD 行动中设置的最后期限。即使用户没有按下导航,它也会导致导航操作(我已经在项目中测试了代码)。 这是因为您在 GCD 队列中累积作业,并且当它们执行时,您处于另一个视图中(由于 0.5 停顿)。顺便说一句,它们会导致导航,因为翻转是观察到的,因此无论谁听,都会执行导航。
无论如何,您要做的是将调度命令更改为:
DispatchQueue.main.async { self.asyncVal.toggle() }
而且导航会更流畅,之后无需执行额外的导航命令。