我在 SwiftUI 和 Combine 中的内存管理方面遇到了一些问题。
例如,如果我有一个 NavigationView,然后导航到带有 TextField 的详细 View ,并在 TextField 中输入一个值并点击后退按钮,那么下次我转到该 View 时,TextField 将具有先前输入的值。
我注意到 View 模型在详细 View 被关闭后仍在内存中,这可能就是 TextField 仍然保持值的原因。
在 UIKit 中,当关闭 ViewController 时, View 模型将被释放,然后在 ViewController 出现时再次创建。这似乎不是这里的情况。
我为此问题附上了一些最低限度的可复制代码。
import SwiftUI
import Combine
struct ContentView: View {
var body: some View {
NavigationView {
NavigationLink(destination: OtherView()) {
Text("Press Here")
}
}
}
}
struct OtherView: View {
@ObservedObject var viewModel = ViewModel()
var body: some View {
VStack {
TextField("Something", text: $viewModel.enteredText)
.textFieldStyle(RoundedBorderTextFieldStyle())
Button(action: {
print("Tap")
}) {
Text("Tapping")
}.disabled(!viewModel.isValid)
}
}
}
class ViewModel: ObservableObject {
@Published var enteredText = ""
var isValid = false
var cancellable: AnyCancellable?
init() {
cancellable = textValidatedPublisher.receive(on: RunLoop.main)
.assign(to: \.isValid, on: self)
}
deinit {
cancellable?.cancel()
}
var textValidatedPublisher: AnyPublisher<Bool, Never> {
$enteredText.map {
$0.count > 1
}.eraseToAnyPublisher()
}
}
我还注意到,例如,如果我在 OtherView 之后添加另一个 View ,比如说 SomeOtherView,那么每次我从 OtherView 输入 TextField 时,都会调用 SomeOtherView 的 View 模型中的 deinit。谁能解释一下为什么会这样?
最佳答案
Moreover, I noticed that if I to a change in ContetView and the view is reevaluated, then I will have two ViewModels in memory
这是由于
ViewModel
中的交叉引用, 这里是固定变体struct OtherView: View, Constructable {
@ObservedObject var viewModel = ViewModel()
var body: some View {
VStack {
TextField("Something", text: $viewModel.enteredText)
.textFieldStyle(RoundedBorderTextFieldStyle())
Button(action: {
print("Tap")
}) {
Text("Tapping")
}.disabled(!viewModel.isValid)
}
.onDisappear {
self.viewModel.invalidate() // << here !!
}
}
}
class ViewModel: ObservableObject {
@Published var enteredText = ""
var isValid = false
var cancellable: AnyCancellable?
init() {
print("[>>] created")
cancellable = textValidatedPublisher.receive(on: RunLoop.main)
.assign(to: \.isValid, on: self)
}
func invalidate() {
cancellable?.cancel()
cancellable = nil
print("[<<] invalidated")
}
deinit {
// cancellable?.cancel() // not here !!!
print("[x] done")
}
var textValidatedPublisher: AnyPublisher<Bool, Never> {
$enteredText.map {
$0.count > 1
}.eraseToAnyPublisher()
}
}
--更新:
is there a way to instantiate OtherView when navigating?
这是一个解决方案(使用 Xcode 11.4/iOS 13.4 测试),但这只是成功的一半,因为一旦创建它就会一直存在,直到导航链接重新验证(即在后面它会保留在内存中直到下一次导航)
struct ContentView: View {
var body: some View {
NavigationView {
NavigationLink(destination:
// create wrapper view with type of view which creation
// is deferred until navigation
DeferCreatingView(of: OtherView.self)) {
Text("Press Here")
}
}
}
}
protocol Constructable {
init()
}
struct DeferCreatingView<T: View & Constructable>: View {
var ViewType: T.Type
init(of type: T.Type) {
ViewType = type
}
var body: some View {
ViewType.init() // << create only here
}
}
struct OtherView: View, Constructable {
// .. not changed code from first part
}
backup
关于ios - View 关闭后 ObservedObject View 模型仍在内存中,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/62474871/