How can I change an #State Variable from an other View - swift

Question

I tried to change an #State Variable with this code (from an other struct, not the struct where I declared the Variable):
MyExampleStruct().myVariable = "New Value"
But it dont worked. I dont know how I can change the value of them, has anybody an idea?
Thanks Boothosh

Answer 1

You aren't going to manipulate the #State of a view directly like that. However, there are plenty of options that you can use to achieve similar results depending on your use case.
Option 1 : Binding
Use when you need to manipulate the variable from both parent and child:
struct ParentView : View {
#State var myVariable : String = "Test"
var body: some View {
VStack {
MyExampleStruct(myVariable: $myVariable)
Button("Change") {
myVariable = "\(Date())"
}
}
}
}
struct MyExampleStruct : View {
#Binding var myVariable : String
var body : some View {
VStack {
Text(myVariable)
Button("Change") {
myVariable = "\(Date())"
}
}
}
}
Option 2: ObservableObject
Use when the state needs to be manipulated in multiple places, passed as a reference via property or via envronmentObject (https://www.hackingwithswift.com/quick-start/swiftui/how-to-use-environmentobject-to-share-data-between-views)
class StateManager : ObservableObject {
#Published var myVariable : String = "Test"
}
struct ParentView : View {
#StateObject var state = StateManager() //use #ObservedObject if targeting iOS 13 or macOS 10.15
var body: some View {
VStack {
MyExampleStruct(state: state)
Button("Change") {
state.myVariable = "\(Date())"
}
}
}
}
struct MyExampleStruct : View {
#ObservedObject var state : StateManager
var body : some View {
Text(state.myVariable)
}
}
Option 3: No state
Use when only the parent needs to manipulate the value:
struct ParentView : View {
#State var myVariable : String = "Test"
var body: some View {
VStack {
MyExampleStruct(myVariable: myVariable)
Button("Change") {
myVariable = "\(Date())"
}
}
}
}
struct MyExampleStruct : View {
var myVariable : String
var body : some View {
Text(myVariable)
}
}

Answer 2

You need to pass it as a Binding to the other view.
For example
struct SubView: View
{
#Binding var myVariable: String
init(_ s: Binding<String>) {
self._myVariable = s
}
var body: some View {
Text(myVariable).onTapGuesture { myVariable = "New Value" }
}
}
struct ContentView: View
{
#State myVariable: String = "Some String"
var body {
SubView($myVariable)
}
}
Of course, this specific example is pretty lame because you hardly need a subview to change a Text string, but you can imagine if you had several views that used myVariable, one of them could change the value, and the others could be responsive to it. It's not the only way, or necessarily even the best way to achieve this in every circumstance. Sometimes you'd want an ObservableObject or an #EnvironmentObject, or with SwiftUI 2, #StateObject.