TipCalculator View Model using FSharp.ViewModule.Core

gistfile1.fs

type TipCalculatorViewModel() as this =
    inherit ViewModelBaseWithNavigation()

    // Create our backing fields
    let subTotal = this.Factory.Backing(<@ this.SubTotal @>, 0.0)
    let receiptTotal = this.Factory.Backing(<@ this.ReceiptTotal @>, 0.0)
    let tipPercent = this.Factory.Backing(<@ this.TipPercent @>, 15.0)

    // This is only used to disable the button
    let handlePaymentCommand = this.Factory.CommandSyncChecked((fun _ -> ()), (fun _ -> false))

    // Add dependencies for INotifyPropertyChanged to be handled correctly
    do
        this.DependencyTracker.AddPropertyDependencies(<@ this.TipAmount @>, [ <@@ this.SubTotal @@> ; <@@ this.ReceiptTotal @@> ; <@@ this.TipPercent @@>])
        this.DependencyTracker.AddPropertyDependencies(<@ this.Total @>, [ <@@ this.SubTotal @@> ; <@@ this.ReceiptTotal @@> ; <@@ this.TipPercent @@>])
    
    member this.SubTotal with get() = subTotal.Value and set(v) = subTotal.Value <- v
    member this.ReceiptTotal with get() = receiptTotal.Value and set(v) = receiptTotal.Value <- v
    member this.TipPercent with get() = tipPercent.Value and set(v) = tipPercent.Value <- v

    member this.TipAmount = Math.Round(this.TipPercent * this.SubTotal / 100.0, 2)

    /// Total value, rounded to nearest quarter.
    member this.Total = Math.Round(4.0 * (this.ReceiptTotal + this.TipAmount)) / 4.0

    member this.HandlePayment = handlePaymentCommand