Passing Data Back from Modals

Sometimes you need data created in a modal to flow back to the parent. Here's how to handle that with closures.

Follow along with the code: iOS-Practice on GitHub

The Problem

A sheet presents a form. When submitted, the parent needs the result. How do you pass data back?

Closure Callback Pattern

struct AddProductSheet: View {
    @Environment(\.dismiss) private var dismiss
    @State private var productName = ""
    let onAdd: (String) -> Void

    var body: some View {
        NavigationStack {
            Form {
                Section("Product Details") {
                    TextField("Product Name", text: $productName)
                }
            }
            .navigationTitle("Add Product")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("Cancel") {
                        dismiss()
                    }
                }
                ToolbarItem(placement: .confirmationAction) {
                    Button("Add") {
                        onAdd(productName)
                        dismiss()
                    }
                    .disabled(productName.isEmpty)
                }
            }
        }
    }
}

Parent View Usage

struct ProductListView: View {
    @State private var showAddSheet = false
    @State private var products: [Product] = []
    @State private var alertMessage = ""
    @State private var showAlert = false

    var body: some View {
        List {
            Button {
                showAddSheet = true
            } label: {
                Label("Add Product", systemImage: "plus.circle.fill")
            }

            ForEach(products) { product in
                Text(product.name)
            }
        }
        .sheet(isPresented: $showAddSheet) {
            AddProductSheet { newProductName in
                // Handle the new product
                alertMessage = "Added: \(newProductName)"
                showAlert = true
            }
        }
        .alert("Success", isPresented: $showAlert) {
            Button("OK") {}
        } message: {
            Text(alertMessage)
        }
    }
}

Full Data Return

For complex data, define a struct:

struct NewProduct {
    let name: String
    let price: Double
    let category: String
}

struct AddProductSheet: View {
    @Environment(\.dismiss) private var dismiss
    @State private var name = ""
    @State private var price = ""
    @State private var category = "Electronics"
    let onAdd: (NewProduct) -> Void

    var body: some View {
        NavigationStack {
            Form {
                TextField("Name", text: $name)
                TextField("Price", text: $price)
                    .keyboardType(.decimalPad)
                Picker("Category", selection: $category) {
                    // ...
                }
            }
            .toolbar {
                ToolbarItem(placement: .confirmationAction) {
                    Button("Add") {
                        let product = NewProduct(
                            name: name,
                            price: Double(price) ?? 0,
                            category: category
                        )
                        onAdd(product)
                        dismiss()
                    }
                }
            }
        }
    }
}

Binding Alternative

For editing existing data, use a binding:

struct EditProductSheet: View {
    @Binding var product: Product
    @Environment(\.dismiss) private var dismiss

    var body: some View {
        Form {
            TextField("Name", text: $product.name)
            // Changes reflect immediately in parent
        }
    }
}

// Parent
.sheet(item: $productToEdit) { $product in
    EditProductSheet(product: $product)
}

When to Use Each

Interview Tip

This demonstrates understanding of data flow in SwiftUI. The closure pattern keeps the modal independent and reusable.