@ObservedObject in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an observed object in a SwiftUI view.

iOS Swift

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

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

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

AMyViewModel

BString

CInt

DView

Attempts:

3 left

💡 Hint

Common Mistakes

Using a struct instead of a class for the observed object.

Forgetting to mark the class with ObservableObject protocol.

You use @ObservedObject to watch an instance of a class that conforms to ObservableObject, like MyViewModel.

2fill in blank

medium

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

iOS Swift

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

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

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

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A-=

B+=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using = instead of +=, which replaces the value instead of adding.

Using the wrong operator like -= which subtracts.

To increase the count by 1, use the += operator.

3fill in blank

hard

Fix the error in the observed object declaration to properly update the view.

iOS Swift

class Counter: ObservableObject {
  var value = 0
}

struct ContentView: View {
  @ObservedObject var counter = [1]()

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

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

APublished

BObservableObject

CCounter

DStateObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the protocol name ObservableObject instead of the class name.

Using @StateObject instead of @ObservedObject in this context.

The observed object must be an instance of the class Counter.

4fill in blank

hard

Fill both blanks to declare a published property and update it correctly.

iOS Swift

class TimerModel: ObservableObject {
  @[1] var seconds = 0

  func tick() {
    seconds [2] 1
  }
}

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APublished

B+=

C-=

DState

Attempts:

3 left

💡 Hint

Common Mistakes

Using @State instead of @Published inside ObservableObject.

Using = instead of += which replaces the value.

Use @Published to mark properties that trigger view updates. Use += to add 1 to seconds.

5fill in blank

hard

Fill all three blanks to create an observed object, update a published property, and display it.

iOS Swift

class ScoreModel: ObservableObject {
  @[1] var score = 0

  func increase() {
    score [2] 10
  }
}

struct ScoreView: View {
  @ObservedObject var model = ScoreModel()

  var body: some View {
    VStack {
      Text("Score: \(model.[3])")
      Button("Add 10") {
        model.increase()
      }
    }
  }
}

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

APublished

B+=

Cscore

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong property name in the Text view.

Forgetting to mark the property with @Published.

Use @Published for the property, += to add 10, and 'score' to display the property.