F# persist some user values for WPF app - wpf

Question

In my small WPF app (F# only) I would like to remember the window size and location after closing. This C# solution suggest to use the projects settings IDictinary for User.config. This looks like the simple approach that I am after but I did not find the project settings in my F# project. Do they exist for F# projects?
I tried this but it does not work: (The save() call as in the C# example is not available.)
let getSetting k def =
if Application.Current.Properties.Contains k
then Application.Current.Properties.Item k
else def
let window = System.Windows.Window()
// is box() the best wax to make floats into obj ?
window.Top <- getSetting "WindowTop" (box 0.0) |> unbox
window.Left <- getSetting "WindowLeft" (box 0.0) |> unbox
window.Height <- getSetting "WindowHeight" (box 800.0) |> unbox
window.Width <- getSetting "WindowWidth" (box 800.0) |> unbox
window.Closing.Add( fun _ ->
Application.Current.Properties.Add("WindowTop",window.Top)
Application.Current.Properties.Add("WindowHeight",window.Height)
Application.Current.Properties.Add("WindowLeft",window.Left)
Application.Current.Properties.Add("WindowWidth",window.Width)
//Application.Current.Properties.Save() // not available!
)
I know I could use a type provider but I would like to keep it simple and without dependencies if possible. Is there a built in way to persist some user values in an F# WPF app?

Answer 1

As #mm8 points out, the approach you mention depends on the Settings.settings file included in the project template of a C# WPF app.
The F# template does not provide such functionality, which is unfortunate given the XAML support is pretty cool. Instead, you could resort to the App.config file:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
...
<appSettings>
<add key="WindowTop" value="0" />
<add key="WindowLeft" value="0" />
<add key="WindowHeight" value="350" />
<add key="WindowWidth" value="525" />
</appSettings>
</configuration>
If you don't want to depend on FSharp.Configuration.dll you can use the ConfigurationManager (note you still need to add a reference to System.Configuration.dll).
open System.Configuration
type UserSettings = {
WindowTop : float
WindowLeft : float
WindowHeight : float
WindowWidth : float
} with
static member Load() =
let config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
{ // To do: add validation
WindowTop = float config.AppSettings.Settings.["WindowTop"].Value
WindowLeft = float config.AppSettings.Settings.["WindowLeft"].Value
WindowHeight = float config.AppSettings.Settings.["WindowHeight"].Value
WindowWidth = float config.AppSettings.Settings.["WindowWidth"].Value
}
member this.Save() =
let config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
config.AppSettings.Settings.["WindowTop"].Value <- string this.WindowTop
config.AppSettings.Settings.["WindowLeft"].Value <- string this.WindowLeft
config.AppSettings.Settings.["WindowHeight"].Value <- string this.WindowHeight
config.AppSettings.Settings.["WindowWidth"].Value <- string this.WindowWidth
config.Save()
Now you can:
open System.Windows
let window = new Window()
let settings = UserSettings.Load()
window.Top <- settings.WindowTop
window.Left <- settings.WindowLeft
window.Height <- settings.WindowHeight
window.Width <- settings.WindowWidth
window.Closing.Add( fun _ ->
{
WindowTop = window.Top
WindowLeft = window.Left
WindowHeight = window.Height
WindowWidth = window.Width
}.Save() )

Answer 2

Thanks to the answer of Funk I came up with this as the minimal general solution using System.Configuration.dll:
module Config =
open System.Configuration
let private config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
let save key value =
try config.AppSettings.Settings.[key].Value <- value
with _ -> config.AppSettings.Settings.Add(key,value) // in case key does not exist yet
config.Save()
let load key =
try Some config.AppSettings.Settings.[key].Value
with _ -> None