Intro
In the previous post, I discussed my continued journey of learning by building a Xamarin.Forms app using F#.
In that post, I discussed the overall architecture:
The architecture above is my attempt at practicing Robert C. Martin’s Clean Architecture. Specifically I make the features of the app the focus of the architecture and I treat everything else as details that are abstracted away via folders.
I treat the integration points of an application as details:
The Integration folder above harbors the modules that integrate with my domain. Such modules would be the application, services, and runtime dependencies.
Types
I began code construction of the application by writing functions to support trade transactions.
The following functions were implemented:
module ManageTradeImpl
open Services
open Core.Entities
open TestAPI
let buyShares (service:IBroker) context balance =
(context , balance) ||> service.TryPurchase
let sellShares (service:IBroker) context =
context |> service.TrySell
Amongst, the various types that were flushed out as I wrote functions, I wrote a Broker interface that will eventually rely on IO.
The broker interface was added to my Services library:
The Broker Interface is the following:
namespace Services
open Core.Entities
type IBroker =
abstract member GetInfo : string -> StockInfo option
abstract member TryPurchase : Shares -> decimal -> PurchaseResult
abstract member TrySell : Shares -> SellResult
abstract member InvestmentsOf : string -> SharesWithPrice seq
Here’s how the buyShares function can get executed:
(*Test*)
let context = { AccountId= "Bizmonger"
Symbol= "ROK"
Qty= 100 }
let result = buyShares (MockBroker()) context 5000m
Here’s the result:
val result : PurchaseResult =
InsufficientFunds {PurchaseAttempt = {AccountId = "Bizmonger";
Symbol = "ROK";
Quantity = 100;};
Balance = 5000M;
StockPrice = 300M;}
Here’s another example for the buyShares function:
(*Test*)
let context = { AccountId= "Bizmonger"
Symbol= "ROK"
Qty= 5 }
let result = buyShares (MockBroker()) context 5000m
Here’s the result:
val result : PurchaseResult = PurchaseRequested {AccountId = "Bizmonger";
Symbol = "ROK";
Quantity = 5;}
The following types have been defined so far for making trades:
module Core.Entities
type StockInfo = {
Symbol : string
Price : decimal
DayLow : decimal
DayHigh : decimal
}
type Shares = {
AccountId : string
Symbol : string
Qty : int
}
type SharesWithPrice ={
Shares : Shares
PricePerShare : decimal
Total : decimal
}
type PurchaseInfo = {
AccountId : string
Symbol : string
Quantity : int
}
type Owner = { AccountId:string ; Symbol:string }
type SellInfo = {
AccountId : string
Symbol : string
Quantity : int
}
type InsufficientFunds = {
PurchaseAttempt : PurchaseInfo
Balance : decimal
StockPrice : decimal
}
type PurchaseResult =
| PurchaseRequested of PurchaseInfo
| UnknownSymbol of PurchaseInfo
| InvalidQuantity of PurchaseInfo
| InsufficientFunds of InsufficientFunds
type SellResult =
| SellRequested of SellInfo
| InsufficientQuantity of SellInfo
User Interface
A domain is useless if there’s no interaction with it.
Here’s a sample UI that was built in XAML:
Here’s the XAML that resulted in the above UI:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:converters="clr-namespace:FnTrade.Converters;assembly=FnTrade" xmlns:home="clr-namespace:Home.ViewModels;assembly=Home" x:Class="FnTrade.HomePage">
<ContentPage.BindingContext>
<home:HomeViewModel />
</ContentPage.BindingContext>
<ContentPage.Resources>
<ResourceDictionary>
<converters:InstanceToBoolConverter x:Key="InstanceToBoolConverter" />
</ResourceDictionary>
</ContentPage.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<ListView x:Name="SharesListView" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" ItemsSource="{Binding Investments}" HorizontalOptions="Center" VerticalOptions="Center">
<ListView.Header>
<Grid >
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Label Grid.Row="0" Grid.Column="0" Text="Symbol" FontAttributes="Bold" HorizontalTextAlignment="Center" />
<Label Grid.Row="0" Grid.Column="1" Text="Qty" FontAttributes="Bold" HorizontalTextAlignment="Center" />
<Label Grid.Row="0" Grid.Column="2" Text="Price" FontAttributes="Bold" HorizontalTextAlignment="Center" />
<Label Grid.Row="0" Grid.Column="3" Text="Total" FontAttributes="Bold" HorizontalTextAlignment="Center" />
<BoxView Grid.Row="1" Grid.ColumnSpan="4" Color="Gray" Margin="5,0,5,5" HorizontalOptions="FillAndExpand" HeightRequest="1" />
</Grid>
</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Text="{Binding Shares.Symbol}" HorizontalTextAlignment="Center" />
<Label Grid.Column="1" Text="{Binding Shares.Qty}" HorizontalTextAlignment="Center" />
<Label Grid.Column="2" Text="{Binding PricePerShare, StringFormat='{}{0:c}'}" HorizontalTextAlignment="Center" />
<Label Grid.Column="3" Text="{Binding Total, StringFormat='{}{0:c}'}" HorizontalTextAlignment="Center" />
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<Button Grid.Row="1" Grid.Column="0" Text="Buy More" Command="{Binding Buy}" CommandParameter="{Binding Source={x:Reference SharesListView}, Path=SelectedItem.Shares.Symbol}" IsEnabled="{Binding Source={x:Reference SharesListView}, Path=SelectedItem, Converter={StaticResource InstanceToBoolConverter}}" />
<Button Grid.Row="1" Grid.Column="1" Text="Sell" Command="{Binding Sell}" CommandParameter="{Binding Source={x:Reference SharesListView}, Path=SelectedItem.Shares.Symbol}" IsEnabled="{Binding Source={x:Reference SharesListView}, Path=SelectedItem, Converter={StaticResource InstanceToBoolConverter}}" />
</Grid>
</ContentPage>
ViewModel
In order for the UI to present dynamic content, I had to implement a viewmodel.
The following viewmodel was implemented:
namespace Home.ViewModels
open System.Windows.Input
open Core.IntegrationLogic
open Core.Entities
open Integration.Factories
open Services
open Search
open System.Collections.ObjectModel
type HomeViewModel() as this =
inherit ViewModelBase()
let dispatcher = getDispatcher()
let accountId = getAccountId()
let broker = getBroker() :> IBroker
let searchCommand =
DelegateCommand( (fun _ -> this.StockInfo <- getQuote broker this.Symbol) , fun _ -> true) :> ICommand
let sellCommand =
DelegateCommand( (fun o -> dispatcher.Sell { Owner.AccountId=accountId ; Symbol=o :?> string} ) ,
fun _ -> true) :> ICommand
let buyCommand =
DelegateCommand( (fun o -> dispatcher.Buy { Owner.AccountId=accountId ; Symbol=o :?> string} ) ,
fun _ -> true) :> ICommand
let mutable symbol = ""
let mutable stockInfo = None
let mutable investments = ObservableCollection<SharesWithPrice>()
member this.Load() =
let result = broker.InvestmentsOf accountId
this.Investments <- ObservableCollection<SharesWithPrice>(result)
member this.Symbol
with get() = symbol
and set(value) = symbol <- value
base.NotifyPropertyChanged(<@ this.Symbol @>)
member this.StockInfo
with get() = stockInfo
and set(value) = stockInfo <- value
base.NotifyPropertyChanged(<@ this.StockInfo @>)
member this.Investments
with get() = investments
and set(value) = investments <- value
base.NotifyPropertyChanged(<@ this.Investments @>)
member this.Search = searchCommand
member this.Sell = sellCommand
member this.Buy = buyCommand
Conclusion
This solution, which is a Work In Process, can be found here on GitHub.
Scott Nimrod's Blog 