我如何动态地为SwiftUI建立一个视图并呈现它?

Question

我包含了存根代码示例。我不知道怎样才能使这个报告生效。我的期望是，当评估表单呈现闭包时，aDependency应该是非nil。然而，正在发生的是aDependency被视为nil，而TheNextView从未被放在屏幕上。

我如何对TheNextView进行建模?我遗漏了什么?

struct ADependency {}
struct AModel {
func buildDependencyForNextExperience() -> ADependency? {
return ADependency()
}
}
struct ATestView_PresentationOccursButNextViewNotShown: View {
@State private var aDependency: ADependency?
@State private var isPresenting = false
@State private var wantsPresent = false {
didSet {
aDependency = model.buildDependencyForNextExperience()
isPresenting = true
}
}
private let model = AModel()

var body: some View {
Text("Tap to present")
.onTapGesture {
wantsPresent = true
}
.sheet(isPresented: $isPresenting, content: {
if let dependency = aDependency {
// Never executed
TheNextView(aDependency: dependency)
}
})
}
}
struct TheNextView: View {
let aDependency: ADependency

init(aDependency: ADependency) {
self.aDependency = aDependency
}

var body: some View {
Text("Next Screen")
}
}

Answer 1

这是iOS 14中常见的问题。sheet(isPresented:)在第一次渲染时被评估，然后没有正确更新。

为了解决这个问题，您可以使用sheet(item:)。唯一的问题是你的项目必须符合Identifiable。

以下版本的代码可以工作:

struct ADependency : Identifiable {
var id = UUID()
}
struct AModel {
func buildDependencyForNextExperience() -> ADependency? {
return ADependency()
}
}
struct ContentView: View {
@State private var aDependency: ADependency?
private let model = AModel()

var body: some View {
Text("Tap to present")
.onTapGesture {
aDependency = model.buildDependencyForNextExperience()
}
.sheet(item: $aDependency, content: { (item) in
TheNextView(aDependency: item)
})
}
}