You should use a State var in Preview and a Binding in the View, as described here:
https://stackoverflow.com/questions/60105438/swiftui-preview-provider-with-binding-variables
Note: when you paste code, it is much better too use Paste And Match Style to avoid all the blank lines:
import SwiftUI
import FirebaseAuth
import FirebaseDatabase
struct SignUp: View {
@State var Value: String = ""
@State var username: String = ""
@State var email: String = ""
@State var password: String = ""
@State var success = false
var body: some View {
NavigationView{
ZStack {
LinearGradient(gradient: Gradient(colors: [Color.blue, Color.white]), startPoint: .topLeading, endPoint: .bottomTrailing)
.ignoresSafeArea()
Rectangle()
.fill(Color.white)
.frame(width: 300, height: 550)
.cornerRadius(10)
VStack(spacing: 30){
Image(systemName: "bitcoinsign.circle")
.font(.system(size: 70, weight: .medium))
.padding()
TextField("Username", text: $username)
.frame(width: 200, height: 30)
.padding()
.overlay(RoundedRectangle(cornerRadius: 10.0).strokeBorder(Color.blue, style: StrokeStyle(lineWidth: 2.0)))
.foregroundColor(.green)
TextField("Email", text: $email)
.frame(width: 200, height: 30)
.padding()
.overlay(RoundedRectangle(cornerRadius: 10.0).strokeBorder(Color.blue, style: StrokeStyle(lineWidth: 2.0)))
.foregroundColor(.green)
TextField("Password", text: $password)
.frame(width: 200, height: 30)
.padding()
.overlay(RoundedRectangle(cornerRadius: 10.0).strokeBorder(Color.blue, style: StrokeStyle(lineWidth: 2.0)))
.foregroundColor(.green)
Button(action: {
createUser(withEmail: email, password: password, username: username)
success = true
}, label: {
Text("Sign Up")
.frame(width: 200, height: 20, alignment: .center)
.padding()
.background(Color.blue)
.foregroundColor(Color.white)
.cornerRadius(15)
})
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
if success == false {
SignUp()
}
else {
Login()
}
}
}
}
func createUser(withEmail email: String, password: String, username: String){
Auth.auth().createUser(withEmail: email, password: password) { (result, error) in
if let error = error {
print("Failed to sign user up", error.localizedDescription)
return
}
else {
guard let uid = result?.user.uid else { return}
let values = ["email": email, "username":username]
Database.database().reference().child(uid).child("users").updateChildValues(values, withCompletionBlock: { (error, ref) in
if let error = error {
print("failed to update databse values with error", error.localizedDescription)
return
}
else {
print("user successfully created..")
}
})
}
}
}
