My Swift program is crashing with :Unexpectedly found nil while unwrapping an Optional value. What does this error mean, and how do I fix it?

Line 30 set the value to showFood, and the line 32 print it ,is not null. but the line 49 show variable showFood is nil and get error. I do not know why.

i have try my best ,but i donot why showFood on line 49 is nil .

code below

import SwiftUI

struct TestView: View {
    @Environment(\.dynamicTypeSize) private var textSize
    @Environment(\.editMode) var editModel
    @State var food = Food.examples
    @State var shouldShowSheet: Bool = false
    @State var selectedFoodID = Set<Food.ID>()
    @State var selectedFood: Binding<Food>?
    var isEditing: Bool {
        editModel?.wrappedValue == .active
    }

    @State var shouldShowForm: Bool = false
    @State var showFood: Food?
    var body: some View {
        VStack(alignment: .leading) {
            List($food, editActions: .all, selection: $selectedFoodID) { $food in
                HStack {
                    Text(food.name)
                        .onTapGesture {
                            showFood = food
                            print(showFood) // showFood here is not null
                        }
                }
            }
        }.sheet(isPresented: $shouldShowSheet, content: {
            let foo = showFood! // showFood is null.  and get error here. i donot why 

        })
    }
}

It's because you forgot to call the showFood getter somewhere in body which is how SwiftUI decides if body needs to be called when a state is set. This usually means you've declared the wrong kind of @State. As a quick fix you can workaround the problem by faking a read like:

sheet(isPresented: $shouldShowSheet) { [showFood] {

But it would be best if you used a different sheet modifier, e.g.

.sheet(item: $showFood) {

Now a new sheet will be recreated when showFood changes and it will have the latest value and not crash.