<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:ViewModel="clr-namespace:ABCD.ViewModel" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"
x:Class="ABCD.SettingsWindow"
x:Name="SettingsWindow1"
Title="SettingsWindow"
Width="640" Height="480">

<Window.Resources>
    <ViewModel:SettingsViewModel x:Key="SettingsViewModelDataSource" d:IsDataSource="True"/>
</Window.Resources>

<Grid x:Name="LayoutRoot" DataContext="{Binding Source={StaticResource SettingsViewModelDataSource}}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="185*"/>
        <ColumnDefinition Width="131*"/>
    </Grid.ColumnDefinitions>
    <Button x:Name="addCurrencyButton" Content="Add Currency" HorizontalAlignment="Left" Height="20" Margin="290,120,0,0" VerticalAlignment="Top" Width="170" Click="addCurrencyButton_Click" Grid.ColumnSpan="2"/>
    <ComboBox x:Name="currencyNamesComboBox" HorizontalAlignment="Left" Height="25" Margin="50,120,0,0" VerticalAlignment="Top" Width="150" ItemsSource="{Binding CurrencyNames}"/>
</Grid>

public class SettingsViewModel:INotifyPropertyChanged
{
    private CurrencyConverter currencyConverter;

    private ObservableCollection<String> currencyNames;

    private ObservableCollection<Double> currencyRates;

    public ObservableCollection<String> CurrencyNames
    {
        get { return currencyNames; }
        set { currencyNames = value; OnPropertyChanged("CurrencyNames"); }
    }


    public ObservableCollection<Double> CurrencyRates
    {
        get { return currencyRates; }
        set { currencyRates = value; OnPropertyChanged("CurrencyRates"); }
    }

    public SettingsViewModel()
    {

        this.CurrencyNames = new ObservableCollection<String>();
        this.CurrencyRates = new ObservableCollection<Double>();
        currencyConverter = new CurrencyConverter();
        UpdateCurrencySettings(currencyConverter.CurrencyNameToRates);
    }

    public void AddCurrency(String currencyName, Double currencyRate)
    {
        currencyConverter.AddNewCurrency(currencyName, currencyRate);
        UpdateCurrencySettings(currencyConverter.CurrencyNameToRates);

    }

    public void RemoveCurrency(String currencyName)
    {
        currencyConverter.RemoveCurrency(currencyName);
        UpdateCurrencySettings(currencyConverter.CurrencyNameToRates);
    }

    private void UpdateCurrencySettings(Dictionary<string, double> currencyNameToRates)
    {
        List<String> currencyNames = new List<String>();
        List<Double> currencyRates = new List<Double>();

        foreach(String key in currencyNameToRates.Keys)
        {
            currencyNames.Add(key);
            currencyRates.Add(currencyNameToRates[key]);
        }
        this.CurrencyNames.Clear();
        this.CurrencyRates.Clear();
        currencyNames.ForEach(item => this.CurrencyNames.Add(item));
        currencyRates.ForEach(item => this.CurrencyRates.Add(item));
    }

    public event PropertyChangedEventHandler PropertyChanged;
    // Create the OnPropertyChanged method to raise the event
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}