Swiftui - 删除列表行

Question

I want to delete a list's row.

I have followed Apple's official SwiftUI tutorials to build this part of my App. You can download SwiftUI Essentials - Handling User Input from https://developer.apple.com/tutorials/swiftui/handling-user-input if you wish so.

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I am using onDelete modifier to delete rows.

        ForEach(filteredLandmarks) { landmark in
            NavigationLink(destination: LandmarkDetail(landmark: landmark)) {
                LandmarkRow(landmark: landmark)
            }
        }
        .onDelete(perform: { indexSet in
            for index in indexSet {
                self.modelData.landmarks.remove(at: index)
            }
        })

It works as long as you do not navigate to LandmarkDetail view. If you do so, the app crushes due to Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value . It is because as you see in the following code, firstIndex is forced unwrapped.

struct LandmarkDetail: View {
    @EnvironmentObject var modelData: ModelData
    
    var landmark: Landmark

    var landmarkIndex: Int {
        modelData.landmarks.firstIndex(where: { $0.id == landmark.id })!
    }

    var body: some View {
      FavoriteButton(isSet: $modelData.landmarks[landmarkIndex].isFavorite)
    }
}

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I can not figure how to allow editing Landmark in LandmarkDetail and also be able to delete it.

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Info

In order to test, Tap on a row to navigate to LandmarkDetail and then navigate back to LandmarkList . Then delete the row that you just tapped on.

Answer 1

The problem is you are removing an index from modelData , but you are sending landmark object from filteredLandmarks variable to LandmarkDetail view (the object is still available in filteredLandmarks ). So, inside LandmarkDetail view, the 'modelData' is not contain the 'landmark' variable you provided.

In LandmarkDetail view:

var landmarkIndex: Int {
    guard let index = modelData.landmarks.firstIndex(where: { return $0.id == landmark.id }) else {
        return 0
    }
    return index
}

OR,

You can try to find out a solution to remove the exact row index from filteredLandmarks variable.