AppStorage property wrapper

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@AppStorage is a property wrapper in SwiftUI that allows you to read and write values to the user's defaults. It's a convenient way to store simple data types like strings, integers, booleans, etc., across app launches.

Looking at the example below.

• @AppStorage("isSwitchOn") private var isSwitchOn: Bool = false declares a property that is bound to the user's defaults. The key "isSwitchOn" is used to identify the value in the defaults. If the value doesn't exist, it defaults to false.
• The Toggle view binds to isSwitchOn, so when the toggle is switched on or off, the value in the user's defaults is updated accordingly.
• The Text view displays the current state of the switch, which is also read from the user's defaults.

What can be stored in AppStorage?

Currently, you can store: Bool, Int, Double, String, URL, Data

Storing structs

You can also store structs that conform to codable by converting it into Data type first and then store in AppStorage as a Data type.

you can put the encode and decode functions inside the struct for convenience but you can put them anywhere or even adapt them to maybe use generics.

Encoding -> Struct -> Data

Decoding -> Data -> Struct

struct UserAppStorage: Codable {
    var name = ""
    var age = 0
    
    func encode() -> Data? {
        let encoder = JSONEncoder()
        if let encoded = try? encoder.encode(self) {
            return encoded
        } else {
            return nil
        }
    }
    
    static func decode(userData: Data) -> UserAppStorage? {
        let decoder = JSONDecoder()
        if let user = try? decoder.decode(UserAppStorage.self, from: userData) {
            return user
        } else {
            return nil
        }
    }
}

as you can see @AppStoragehas a default value of a data. we call the encode function to get our struct to convert to data.

Alternative @AppStorage Initializers

It’s easy to see how using the initializers could be confusing and misleading to developers who are new to @AppStorage.

Developers are used to associating this kind of syntax when assigning a value to a variable. So it’s easy to think an @AppStorage key is being created and using this value.

Both of these initializers do the exact same thing.

@AppStorage("isToggleTrue") var isToggleTrue = false
// OR
@AppStorage(wrappedValue: false, "isToggleTrue") var isToggleTrue

The wrappedValue is the default value used if the isToggleTrue key does not exist in app storage.

when to use:

• You want to store small amounts of data
• You want data to persist when the app closes
• You want to be able to bind directly to the values stored in @AppStorage

References

Big Mountain Studio SwiftUI Resources

GitHub: https://github.com/abdahad1996/SwiftUI_Bootcamp/blob/main/SwiftUI_Bootcamp/SwiftUI_Bootcamp/AppStorage/AppStorage.swift