SwiftUI中的ObservedObject和StateObject有什么区别

问题描述

如果我在SwiftUI中有一个ObservableObject，我可以将其称为@ObservedObject:

If I have an ObservableObject in SwiftUI I can refer to it as an @ObservedObject:

class ViewModel: ObservableObject {
    @Published var someText = "Hello World!"
}

struct ContentView: View {
    @ObservedObject var viewModel = ViewModel()

    var body: some View {
        Text(viewModel.someText)
    }
}

或作为@StateObject:

class ViewModel: ObservableObject {
    @Published var someText = "Hello World!"
}

struct ContentView: View {
    @StateObject var viewModel = ViewModel()

    var body: some View {
        Text(viewModel.someText)
    }
}

但是两者之间的实际区别是什么?有没有一种情况比另一种更好，或者它们是两种完全不同的情况?

But what's the actual difference between the two? Are there any situations where one is better than the other, or they are two completely different things?

推荐答案

@ObservedObject

当视图创建自己的@ObservedObject实例时，每次丢弃并重绘视图时都会重新创建该视图:

When a view creates its own @ObservedObject instance it is recreated every time a view is discarded and redrawn:

struct ContentView: View {
  @ObservedObject var viewModel = ViewModel()
}

相反，当重绘视图时，@State变量将保留其值.

On the contrary a @State variable will keep its value when a view is redrawn.

@StateObject

A @StateObject是@ObservedObject和@State的组合-即使丢弃视图并重画视图后，ViewModel的实例也将保留并重新使用:

A @StateObject is a combination of @ObservedObject and @State - the instance of the ViewModel will be kept and reused even after a view is discarded and redrawn:

struct ContentView: View {
  @StateObject var viewModel = ViewModel()
}

性能

虽然@ObservedObject会经常迫使View重新创建一个重量级的对象，但会影响性能，但是@ObservedObject不复杂时，它并不重要.

Although an @ObservedObject can impact the performance if the View is forced to recreate a heavy-weight object often, it should not matter much when the @ObservedObject is not complex.

何时使用@ObservedObject

现在看来没有理由使用@ObserverObject，所以什么时候应该使用它?

It might appear there is no reason now to use an @ObserverObject, so when should it be used?

请注意，可能有太多用例，有时可能需要来在视图中重新创建可观察的属性.在这种情况下，最好使用@ObservedObject.

Note there are too many use-cases possible and sometimes it may be desired to recreate an observable property in your View. In that case it's better to use an @ObservedObject.

有用的链接:

• @StateObject和@ObservedObject有什么区别?
• @StateObject属性包装器是什么?

• What’s the difference between @StateObject and @ObservedObject?
• What is the @StateObject property wrapper?

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