My view needs an environment object which is set in the SceneDelegate by adding it to the window.rootViewController. How can I set an environment object to be used for the preview?
You add it using .environmentObject(_:) modifier:
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
.environmentObject(YourObject())
}
}
This userData property gets its value automatically, as long as the environmentObject(_:) modifier has been applied to a parent.
struct UserList: View {
#EnvironmentObject var userData: UserData
var body: some View {
NavigationView {
List {
Toggle(isOn: $userData.showFavoritesOnly) {
Text("Users Fav only")
}
ForEach(landmarkData) { landmark in
if !self.userData.showFavoritesOnly || landmark.isFavorite {
NavigationLink(destination: LandmarkDetail(landmark: landmark)) {
UserRow(landmark: landmark)
}
}
}
}
.navigationBarTitle(Text("Users"))
}
}
}
struct UserList_Previews: PreviewProvider {
static var previews: some View {
UserList()
.environmentObject(UserData())
}
}
Related
So I am still learning Swift and for some reason, I am having the hardest trouble with the previews and how to configure them.
So I have the following code:
struct MainView: View {
// The app's model that the containing scene passes in
#ObservedObject var model: MainViewModel
#State var activeTab = 0
var body: some View {
VStack {
TabView(selection: $activeTab) {
Group {
WorldView(model: model, activeTab: $activeTab)
.tabItem {
Label(Tabs.explore.rawValue, systemImage: Tabs.explore.icon)
.environment(\.symbolVariants, .none)
}
.tag(0)
ListView(model: model, activeTab: $activeTab)
.tabItem {
Label(Tabs.list.rawValue, systemImage: Tabs.list.icon)
.environment(\.symbolVariants, .none)
}
.tag(1)
FavoritesView(activeTab: $activeTab)
.tabItem {
Label(Tabs.favorite.rawValue, systemImage: Tabs.favorite.icon)
.environment(\.symbolVariants, .none)
}
.tag(2)
ProfileView(model: model, activeTab: $activeTab)
.tabItem {
Label(Tabs.profile.rawValue, systemImage: Tabs.profile.icon)
.environment(\.symbolVariants, .none)
}
.tag(3)
}
.environmentObject(model)
}
.tint(.accentColor)
.onChange(of: activeTab, perform: { value in
log.info("\n 🟢: (MainView: 46) - User has selected tab: \(value).")
print("")
})
}
.onAppear() {
model.fetchPlaces()
}
}
}
Then I have the preview, as such:
struct MainView_Previews: PreviewProvider {
static var previews: some View {
MainView(model: model, activeTab: activeTab)
}
}
I am getting the two errors on the previews:
Cannot find 'activeTab' in scope
Cannot find 'model' in scope
If I define it as such:
struct MainView_Previews: PreviewProvider {
#ObservedObject var model: MainViewModel
#State var activeTab = 0
static var previews: some View {
MainView(model: model, activeTab: activeTab)
}
}
I get the following errors:
Instance member 'activeTab' cannot be used on type 'MainView_Previews'
Instance member 'model' cannot be used on type 'MainView_Previews'
Does anyone know how I can configure the preview so that it works properly and doesn't crash?
This happens because you are either passing in non existing paremeters in Previews, or because you cannot initialize objects in previews. Instead, do this:
struct MyExamplePreviews: PreviewProvider{
static var previews: some View {
MainView(model: MainViewModel(), activeTab: 0)
}
}
This will allow you to preview the UI. What this does:
Creates a new model that is passed in at the top level - again, you cannot create this anywhere but right here in the previews
Makes it so that activeTab will be set to 0 - you can have multiple preview devices with different tabs if needed. See the docs for Previews to learn more.
I recommend the below approach, then you can use #EnvironmentObject var model: Model in any View that needs it and don't have to pass it into every View.
class Model: ObservableObject {
#Published var items: [Item] = []
static var shared = Model()
static var preview = Model(preview: true)
init(preview: Bool) {
if preview {
items = // set some test items
return
}
load()
}
fun load(){
// load items from disk
}
}
#main
struct TestApp: App {
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(Model.shared)
}
}
}
struct ContentView: View {
#EnvironmentObject var: model: Model
var body: some View {
NavigationStack {
List {
ForEach($model.items) $item in {
TextField("Title" text: $item.title)
}
.navigationTitle("Items")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
.environmentObject(Model.preview)
}
}
I am engaging in a small SwiftUI exercise to learn how to pass data between views using NavigationLink. I set up ContentView to send a message to the SecondView after tapping the ContentView NavigationLink. Tapping NavigationLink in the SecondView then sends the message to the ThirdView. However, I am noticing a strange UI occurrence by the time I get to ThirdView. See the screenshot below:
Any idea why this NavigationView issue is occurring? Is it related to having NavigationView in all 3 views?
Here is my code:
ContentView
struct ContentView: View {
var body: some View {
NavigationView {
NavigationLink(destination: SecondView(message: "Hello from ContentView")) {
Text("Go to Second View")
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
SecondView
struct SecondView: View {
var message: String
var body: some View {
Text("\(message)")
NavigationView {
NavigationLink(destination: ThirdView(message: self.message)) {
Text("Go to Third View")
}
}
}
}
struct SecondView_Previews: PreviewProvider {
static var previews: some View {
SecondView(message: String())
}
}
ThirdView
struct ThirdView: View {
var message: String
var body: some View {
NavigationView {
Text("\(message)")
}
}
}
struct ThirdView_Previews: PreviewProvider {
static var previews: some View {
ThirdView(message: String())
}
}
Feedback is appreciated. Thanks!
remove the second navigation view
struct SecondView: View {
var message: String
var body: some View {
VStack(spacing: 100 ) {
Text("\(message)")
NavigationLink(destination: ThirdView(message: self.message)) {
Text("Go to Third View")
}
}
}
}
struct ThirdView: View {
var message: String
var body: some View {
Text("\(message)")
}
}
I originally posted another question asking this in the context of a project I was trying to develop, but I can't even get it to work in a vacuum so I figured I'd start with the basics. As the title suggests, my EnvironmentObjects don't update the UI as they should; in the following code, the user enters text on the ContentView and should be able to see that text in the next screen SecondView.
EDITED:
import SwiftUI
class NameClass: ObservableObject {
#Published var name = ""
}
struct ContentView: View {
#StateObject var myName = NameClass()
var body: some View {
NavigationView {
VStack {
TextField("Type", text: $myName.name)
NavigationLink(destination: SecondView()) {
Text("View2")
}
}
}.environmentObject(myName)
}
}
struct SecondView: View {
#EnvironmentObject var myself: NameClass
var body: some View {
Text("\(myself.name)")
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
.environmentObject(NameClass())
}
}
However, the SecondView doesn't show the text that the user has written, but the default value of name (blank). What am I doing wrong here?
class NameClass: ObservableObject {
#Published var name = ""
}
struct ContentView: View {
#StateObject var myName = NameClass()
var body: some View {
NavigationView {
VStack {
TextField("Type", text: $myName.name)
NavigationLink(destination: SecondView()) {
Text("View2")
}
}
}.environmentObject(myName)
}
}
struct SecondView: View {
#EnvironmentObject var myself: NameClass
var body: some View {
Text("\(myself.name)")
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
.environmentObject(NameClass())
}
}
I'm back with another question. I was following this guide: https://medium.com/#fs.dolphin/passing-data-between-views-in-swiftui-793817bba7b1
Everything worked from it, but the SecondView_Previews is throwing an error Missing argument for parameter 'message' in call. Here is my ContentView and SecondView
// ContentView
import SwiftUI
struct ContentView: View {
#State private var showSecondView = false
#State var message = "Hello from ContentView"
var body: some View {
VStack {
Button(action: {
self.showSecondView.toggle()
}){
Text("Go to Second View")
}.sheet(isPresented: $showSecondView){
SecondView(message: self.message)
}
Button(action: {
self.message = "hi"
}) {
Text("click me")
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
import SwiftUI
struct SecondView: View {
#State var message: String
var body: some View {
Text("\(message)")
}
}
struct SecondView_Previews: PreviewProvider {
static var previews: some View {
SecondView() // Error here: Missing argument for parameter 'message' in call.
}
}
It tried changing it to SecondView(message: String) and the error changes to "Cannot convert value of type 'String.Type' to expected argument type 'String'"
Can someone please explain what I'm doing wrong, or how to correctly set up the preview. It all works fine when there's no preview. Thanks in advance!
struct ContentView: View {
#State var message: String //Define type here
var body: some View {
Text("\(message)")
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView(message: "Some text") //Passing value here
}
}
I am learning Modals in SwiftUI and the code is below:
ContentView.swift:
import SwiftUI
struct ContentView: View {
#State private var showingAddUser = false
var body: some View {
return VStack {
Text("Modal View")
}.onTapGesture {
self.showingAddUser.toggle()
print(self.showingAddUser) //for console
}
.sheet(isPresented: $showingAddUser) {
Addview(isPresented: self.$showingAddUser)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
AddView.swift:
import SwiftUI
struct Addview: View {
#Binding var isPresented: Bool
var body: some View {
Button("Dismiss") {
self.isPresented = false
}
}
}
struct Addview_Previews: PreviewProvider {
static var previews: some View {
Addview(isPresented: .constant(false))
}
}
When I try to run the code for the first time and check the print output in console, boolean value changes to true however if I initialise #State variable showingAddUser with true the console output is unchanged that is it remains true. Should't toggle() flip the boolean value to false?
Is this toggle() different from Toggle switch from a concept point of view?
The toggle() is a mutating function on value type Bool. If you set the initial value of showingAddUser as true it will display the AddUser View when launched initially and it's not if set to false, that's the difference.
Toggle is a SwiftUI View. It can be used as any other View in SwiftUI body, like this:
struct ContentView: View {
#State var bool: Bool
var body: some View {
Toggle(isOn: $bool) {
Text("Hello world!")
}
}
}
There is no need for isPresented Boolean in Add View
Try This
ContentView.swift
import SwiftUI
struct ContentView: View {
#State private var showingAddUser = false
var body: some View {
return VStack {
Text("Modal View")
}.onTapGesture {
self.showingAddUser = true
print(self.showingAddUser) //for console
}
.sheet(isPresented: $showingAddUser) {
Addview()
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
AddView.swift
import SwiftUI
struct AddView: View {
var body: some View {
Button(action:
// Do Your Things
) {
Text("MyButton")
}
}
}
struct Addview_Previews: PreviewProvider {
static var previews: some View {
Addview()
}