SwiftUI:什么是@AppStorage属性包装器 [英] SwiftUI: What is @AppStorage property wrapper
问题描述
我曾经使用以下语句将重要的App数据(例如登录凭据)保存到UserDefaults中:
I used to save important App data like login credentials into UserDefaults using the following statement:
UserDefaults.standard.set("sample@email.com", forKey: "emailAddress")
现在，我知道SwiftUI引入了新的属性包装器:
Now, I have come to know SwiftUI has introduced new property wrapper called:
@AppStorage
@AppStorage
任何人都可以解释一下新功能的工作原理吗?
Could anyone please explain how the new feature works?
推荐答案
@AppStorage是一种方便的方法，可以从UserDefaults中保存和读取变量，并以与@State属性相同的方式使用它们.可以将其视为@State属性，该属性会自动保存到UserDefaults(并从中读取).
@AppStorage is a convenient way to save and read variables from UserDefaults and use them in the same way as @State properties. It can be seen as a @State property which is automatically saved to (and read from) UserDefaults.
您可以想到以下几点:
@AppStorage("emailAddress") var emailAddress: String = "sample@email.com"
与此等效(在SwiftUI中不允许 且将 not 进行编译):
as an equivalent of this (which is not allowed in SwiftUI and will not compile):
@State var emailAddress: String = "sample@email.com" {
get {
UserDefaults.standard.string(forKey: "emailAddress")
}
set {
UserDefaults.standard.set(newValue, forKey: "emailAddress")
}
}
请注意，@AppStorage的行为类似于@State:对其值的更改将使View无效并重新绘制视图.
Note that @AppStorage behaves like a @State: a change to its value will invalidate and redraw a View.
默认情况下，@AppStorage将使用UserDefaults.standard.但是，您可以指定自己的UserDefaults商店:
By default @AppStorage will use UserDefaults.standard. However, you can specify your own UserDefaults store:
@AppStorage("emailAddress", store: UserDefaults(...)) ...
有用的链接:
- What is the @AppStorage property wrapper?
- AppStorage Property Wrapper SwiftUI
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