Swift UI 没有考虑数值

Question

我正在尝试为这个等式添加一个额外的数值，但 swift UI 似乎忽略了这个数字。除 0.30 这个附加值外，其他一切都正常工作并显示正确的数字。我已经用各种方式重写了，但仍然没有考虑到 0.30。

@State private var itemPaid = ""
@State private var itemSold = ""
@State private var itemShipping = ""

var totalProfit: Double {
    let broughtPrice = Double(itemPaid) ?? 0
    let paidPrice = Double(itemSold) ?? 0
    let shippingCost = Double(itemShipping) ?? 0
    let percent = Double(2.9 / 100) * broughtPrice + 0.30 <---
    or let fee = 0.30 <---

    let itemCost = paidPrice - broughtPrice
    let totalExpense = shippingCost + percent
    let total = itemCost - totalExpense
    
    return total
}

var body: some View {
if #available(iOS 16.0, *) {
            
            TextField("Item Brought Price", text: $itemPaid)
                .keyboardType(.decimalPad)
                .multilineTextAlignment(.center)
                .padding()

            
            TextField("Item Sold Price", text: $itemSold)
                .keyboardType(.decimalPad)
                .multilineTextAlignment(.center)
                .padding()

            TextField("Shipping Cost", text: $itemShipping)
                .keyboardType(.decimalPad)
                .multilineTextAlignment(.center)
                .padding()

        Section(header:
                    
            Text("Total Profit").font(.system(size: 20))) {
            Text("£\(totalProfit, specifier: "%.2f")")
                .foregroundColor(.green)
                .font(.system(size: 25))
            
        }
        .textCase(nil)