Why variable in SwiftUI not get refreshed?

true is set to isJsonToLoad when Button get pressed:

Button(action: {
    showDocumentPicker = true
    isJsonToLoad = true // <----
    
}){ Text("Load JSON schema").padding() }

but here it is not active yet, so if statement will not be triggered. Why it is not true?

}.sheet(isPresented: self.$showDocumentPicker) {
    if isJsonToLoad { // <----
        DocumentPicker(filePath: $jsonURL)
    } else if isJsonSchemaToLoad {
        DocumentPicker(filePath: $jsonSchemaURL)
    }
}

and some more code:

import SwiftUI
import JSONSchema

struct ContentView: View {
    
    var d1: [String: Any]? = nil
    var res: ValidationResult?
    let documentPicker = UIDocumentPickerViewController(forOpeningContentTypes: [.json])
    @State private var showDocumentPicker = false
    @State private var isJsonToLoad = false
    @State private var isJsonSchemaToLoad = false
    @State private var jsonURL = URL(string: "")
    @State private var jsonSchemaURL = URL(string: "")
    
    init() {
        updateValue()
        return
    }
    
    mutating func updateValue() {
        do {
            if let jsonURL = Bundle.main.url(forResource: "user", withExtension: "json") {
                let jsonData = try Data(contentsOf: jsonURL)
                let d = try JSONSerialization.jsonObject(with: jsonData)
                res = try JSONSchema.validate(d, schema: [
                    "type": "object",
                    "properties": [
                        "name": ["type": "string"],
                        "price": ["type": "number"],
                    ],
                    "required": ["name"],
                ])
                d1 = d as? [String: Any]
            }
        } catch  {
            
        }
    }
    
    
    func showNode(json: [String: Any], depth: Int = 1) -> AnyView {
        return AnyView(VStack {
            ForEach(json.keys.sorted(), id: \.self) { k in
                if let str = json[k] as? String {
                    Text("\(k) \(str)").padding()
                } else if let i = json[k] as? Int {
                    Text("\(k) \(i)").padding()
                } else if let d2 = json[k] as? [String: Any] {
                    Text("\(k)").padding()
                    showNode(json: d2)
                }
            }
        })
    }
    
    
    var body: some View {
        VStack {
            Button(action: {
                showDocumentPicker = true
                isJsonToLoad = true
                
            }){ Text("Load JSON schema").padding() }
            
            Button(action: {
                showDocumentPicker = true
                isJsonSchemaToLoad = true
            }){ Text("Load JSON").padding() }
                
            
            Text("\(res?.errors != nil ? "Invalid XML" : "Valid XML")")
                .padding()
            Divider()
           
            Text("\(self.jsonURL?.absoluteString.description ?? "")")
                .padding()
            
            Divider()
            Text("\(self.jsonSchemaURL?.absoluteString.description ?? "")")
                .padding()
            
            Divider()
            if let d1 = self.d1 {
                showNode(json: d1)
            }
        }.sheet(isPresented: self.$showDocumentPicker) {
            if isJsonToLoad {
                DocumentPicker(filePath: $jsonURL)
            } else if isJsonSchemaToLoad {
                DocumentPicker(filePath: $jsonSchemaURL)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}