How could I initialize the @State variable in the init function in SwiftUI?

Question

Let's see the simple source code:

import SwiftUI

struct MyView: View {
    @State var mapState: Int
    
    init(inputMapState: Int)
    {
        mapState = inputMapState //Error: 'self' used before all stored properties are initialized
    } //Error: Return from initializer without initializing all stored properties
    
    var body: some View {
        Text("Hello World!")
    }
}

I need the init function here because I want to do some data loading here, but there is one problem, the @State variable could not be initialize here! How could I do with that? Maybe it's a very simple question, but I don't know how to do. Thanks very much!

question from:https://stackoverflow.com/questions/58758370/how-could-i-initialize-the-state-variable-in-the-init-function-in-swiftui

Answer 1

Property wrappers are generating some code for you. What you need to know is the actual generated stored property is of the type of the wrapper, hence you need to use its constructors, and it is prefixed with a _. In your case this means var _mapState: State<Int>, so following your example:

import SwiftUI

struct MyView: View {
    @State var mapState: Int

    init(inputMapState: Int)
    {
        _mapState = /*State<Int>*/.init(initialValue: inputMapState)
    }

    var body: some View {
        Text("Hello World!")
    }
}