@StateObject for observable objects in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an observable object using @StateObject in a SwiftUI view.

iOS Swift

struct ContentView: View {
  @StateObject var viewModel = [1]()

  var body: some View {
    Text(viewModel.title)
  }
}

Drag options to blanks, or click blank then click option'

AObservableObject

BMyViewModel

CStateObject

DViewModel

Attempts:

3 left

💡 Hint

Common Mistakes

Using @StateObject with a protocol name instead of a class.

Forgetting to create an instance by calling () after the class name.

You use your custom class name that conforms to ObservableObject with @StateObject to create and own it in the view.

2fill in blank

medium

Complete the code to update the view when the observable object changes.

iOS Swift

class MyViewModel: ObservableObject {
  @Published var count = 0
}

struct ContentView: View {
  @StateObject var viewModel = MyViewModel()

  var body: some View {
    Button(action: {
      viewModel.[1] += 1
    }) {
      Text("Count: \(viewModel.count)")
    }
  }
}

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Acount

BobjectWillChange

Cupdate

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to update objectWillChange directly.

Using a property that does not exist in the view model.

The @Published property 'count' is updated to trigger the view refresh.

3fill in blank

hard

Fix the error in the code by completing the declaration of the observable object in the view.

iOS Swift

struct ContentView: View {
  [1] var viewModel = MyViewModel()

  var body: some View {
    Text("Count: \(viewModel.count)")
  }
}

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A@StateObject

B@EnvironmentObject

C@ObservedObject

D@Published

Attempts:

3 left

💡 Hint

Common Mistakes

Using @ObservedObject which does not own the object and can cause multiple instances.

Using @Published which is only for properties inside observable objects.

@StateObject is used to create and own the observable object in the view lifecycle.

4fill in blank

hard

Fill both blanks to declare an observable object class and use it with @StateObject in a SwiftUI view.

iOS Swift

class [1]: ObservableObject {
  @Published var message = "Hello"
}

struct ContentView: View {
  @StateObject var viewModel = [2]()

  var body: some View {
    Text(viewModel.message)
  }
}

Drag options to blanks, or click blank then click option'

AGreetingViewModel

BMessageViewModel

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the class and the instance.

Forgetting to add () when creating the instance.

The class name and the instance type must match exactly for the code to compile and work.

5fill in blank

hard

Fill all three blanks to create an observable object with a published property and use it in a SwiftUI view with @StateObject.

iOS Swift

class [1]: ObservableObject {
  @Published var [2] = 0
}

struct ContentView: View {
  @StateObject var viewModel = [3]()

  var body: some View {
    Text("Value: \(viewModel.value)")
  }
}

Drag options to blanks, or click blank then click option'

ACounterModel

Bvalue

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name different from the one displayed in the Text view.

Mismatching class name and instance name.

The class name and instance must match, and the published property name must be consistent with the usage in the view.