SwiftUI - 更新 @State 不会改变视图

Question

I'm kind of new with SwiftUI, and i want to create a login screen with "Quick developers access" button (aka "User1"), that should fill up the user and password fields.

When I click on the "User1" button, the @State phone and password variables of LoginScreen are filling up correctly with the correct values, but the CustomLoginField is no showing the updated values.

I also tried to use @Binding var phone:String instead @State , but same result.

I know that @State should be private.. so i also would like to know the right way to write my code.

import SwiftUI

struct LoginScreen: View {
    
    private let developers:[User] = [
        .init(name: "User1", phone: "12345678", password: "1234")]
    
    private let minSpaceFromBottom:CGFloat = 30
    @State fileprivate var phone:String = ""
    @State fileprivate var password:String = ""
    
    var body: some View {
        GeometryReader { geo in
            ZStack {
                Color(#colorLiteral(red: 0.9965313077, green: 0.9966740012, blue: 0.9965001941, alpha: 1))
                VStack(alignment: .center) {
                    Spacer().frame(height: geo.safeAreaInsets.top)
                        
                    CustomLoginField(inputStr:phone, keyboard: .numberPad, placeholder:"PHONE", formatedPhoneNumber:true, maxLength: 10)
                    CustomLoginField(inputStr:password, keyboard: .numberPad, placeholder: "PASSWORD", isSecure: true, maxLength: 4)
                       
                            HStack {
                                ForEach(developers, id:\.id) { developer in
                                    Text(developer.name!)
                                        .frame(width: 70, height: 35, alignment: .center)
                                        .onTapGesture {
                                            phone = developer.phone
                                            password = developer.password
                                        }
                                }
                        }
                        
                        Spacer()
                        
                    }
                    .frame(width: geo.size.width * 0.9, alignment: .leading)
                    Spacer()
                        .frame(height: minSpaceFromBottom)
                }
            }
    }
}

private struct CustomLoginField: View {
    
    @State var inputStr:String
    var keyboard:UIKeyboardType = .default
    var placeholder:String
    var isSecure:Bool = false
    var formatedPhoneNumber = false
    var maxLength = 0
    var underlineColor:UIColor {
        let underlineOnColor = UIColor(.blue)
        let underlineOffColor:UIColor = .lightGray
        return inputStr.count >= maxLength ? underlineOnColor : underlineOffColor
    }
    
    var body: some View {
        
        VStack(alignment:.leading, spacing:-8) {
            Text(placeholder)
                .opacity(!inputStr.isEmpty ? 1 : 0)
                .animation(Animation.easeIn(duration: !inputStr.isEmpty ? 0.3 : 0))
            
            if isSecure {
                SecureField(placeholder, text: $inputStr)
                    .modifier(CustomTextFieldModifire(parent: self))
            } else {
                TextField(placeholder, text: $inputStr)
                    .modifier(CustomTextFieldModifire(parent: self))
            }
            
            Color(underlineColor)
                .frame(width: UIScreen.main.bounds.width * 0.88, height: 1)
                .animation(Animation.easeIn(duration:0.3))
        }
    }
}

private struct CustomTextFieldModifire: ViewModifier {
    var parent:CustomLoginField
    
    func body(content: Content) -> some View {
        content
            .frame(height: 45)
            .keyboardType(parent.keyboard)
            .onReceive(parent.inputStr.publisher.collect()) {
                var result = String($0)
                
                if parent.maxLength > 0 && result.count > parent.maxLength {
                    result = String(result.prefix(parent.maxLength))
                }
                
                parent.inputStr = result
            }
    }
}

private struct User:Identifiable {
    let id = UUID()
    var name:String?
    var phone:String
    var password:String
}

struct LoginScreen_Previews: PreviewProvider {
    static var previews: some View {
        LoginScreen()
            .previewDevice("iPhone 8")
    }
}

Answer 1

you just made a minor mistake.

In customloginField, you need to define inputStr: String as a binding variable

@Binding var inputStr:String

and while using, you have to use it as following

CustomLoginField(inputStr:self.$phone, keyboard: .numberPad, placeholder:"PHONE", formatedPhoneNumber:true, maxLength: 10)
CustomLoginField(inputStr:self.$password, keyboard: .numberPad, placeholder: "PASSWORD", isSecure: true, maxLength: 4)

Noticed "$" before phone & password?

Check below SO thread for the @state vs @binding SwiftUI @State vs Binding