如何在MVVM中实现appSettings

我正在尝试摆脱我使用的警告appSettings在 WPF 项目中。

应用程序配置

<?xml version="1.0" encoding="utf-8"?>
<configuration>

  ...

  <appSettings>
    <add key="Language" value="English" />
    <add key="Department" value="Production" />
  </appSettings>
</configuration>

Model

open System.Configuration

type UserSettings = {
    Language    : string
    Department  : string
} with 
    static member Null =
        {
        Language    = "English"
        Department  = "Production"
        }
    static member Load() =
        let config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
        {
        Language    = config.AppSettings.Settings.["Language"].Value
        Department  = config.AppSettings.Settings.["Department"].Value
        }
    member this.Save() =
        let config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
        config.AppSettings.Settings.["Language"].Value   <- this.Language
        config.AppSettings.Settings.["Department"].Value <- this.Department
        config.Save() 

视图模型

open FSharp.ViewModule

type SettingsViewModel() as self = 
    inherit ViewModelBase()    

    let settings    = UserSettings.Load()

    let department  = self.Factory.Backing(<@ self.Department @>, settings.Department)

    ...

View

<Window 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:ViewModels;assembly=mySolution"
    xmlns:fsxaml="http://github.com/fsprojects/FsXaml"
    Title="{Binding Department}" Height="300" Width="400">
    <Window.DataContext>
        <local:SettingsViewModel/>
    </Window.DataContext>

    ...

</Window>

视觉设计师划定界限<local:SettingsViewModel/>并给出警告：

未将对象引用设置为引用的实例。

这似乎是由各个层 (MVVM) 的启动顺序引起的。

Changing

let settings    = UserSettings.Load()

to

let settings    = UserSettings.Null

解决警告。

第二种方法

open FSharp.Configuration
type configSettings = AppSettings<"app.config">

这次的线路<local:SettingsViewModel/>给出错误（仍然构建）：

错误 1 ​​在配置的“appSettings”部分找不到名称语言 文件。 (C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\XDesProc.exe.Config)

有没有办法实现appSettings这不会导致警告/错误？

EDIT

第二种方法使用的层：

Model

open FSharp.Configuration
type UserSettings = AppSettings<"app.config">

视图模型

open FSharp.ViewModule

type SettingsViewModel() as self = 
    inherit ViewModelBase()    

    let department  = self.Factory.Backing(<@ self.Department @>, UserSettings.Department)

    ...