Ich verstehe nicht, warum in meinem folgenden Beispiel das Kombinationsfeld "Abrechnungsmodell" nicht die Eigenschaft BillingModel.BillingModelDescription anzeigt, wenn das Textfeld dies tut. Nach der Auswahl eines Kunden möchte ich, dass das Kombinationsfeld die aktuelle Beschreibung des Rechnungsmodells anzeigt, aber es bleibt leer. Das an dasselbe Objekt gebundene Textfeld enthält die Beschreibung. Ich habe eine Sammlung von möglichen Modellen als ItemsSource, die gut funktioniert. Wie aktualisiere ich das Kombinationsfeld Abrechnungsmodell bei Auswahl eines Kunden?

Hier ist die XAML:

<Window x:Class="WpfApplication7.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<StackPanel>
    <StackPanel Orientation="Horizontal">
        <Label Content="Client"/>
    <ComboBox ItemsSource="{Binding AllClientData}" DisplayMemberPath="EmployerStr"
              SelectedItem="{Binding SelectedClient}"
              Width="300"/>
    </StackPanel>
    <StackPanel Orientation="Horizontal">
        <Label Content="Billing Model:"/>
    <ComboBox ItemsSource="{Binding AllBillingModels}" DisplayMemberPath="BillingModelDescription"
              SelectedItem="{Binding SelectedClient.BillingModel}"
              Width="300"/>
    </StackPanel>
    <StackPanel Orientation="Horizontal">
        <Label Content="Billing Model" />
    <TextBox Text="{Binding SelectedClient.BillingModel.BillingModelDescription}" Width="200"/>
    </StackPanel>
</StackPanel>

Und der Code-Behind (dies ist nur ein Beispiel, ich verwende MVVM usw. in der vollständigen App, aber dies dient meinem Zweck, um das Problem zu veranschaulichen):

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public MainWindow()
    {
        AllClientData = new ObservableCollection<ClientRate>();
        AllBillingModels = new ObservableCollection<BillingModelType>();

        ClientRate uno = new ClientRate();
        uno.BillingModel = new BillingModelType();
        uno.BillingModel.BillingModelID = 3;
        uno.BillingModel.BillingModelDescription = "Free";
        uno.ID = 01;
        uno.EmployerName = "Employer1";

        ClientRate dos = new ClientRate();
        dos.BillingModel = new BillingModelType();
        dos.BillingModel.BillingModelID = 2;
        dos.BillingModel.BillingModelDescription = "Variable";
        dos.ID = 02;
        dos.EmployerName = "Employer2";

        ClientRate tre = new ClientRate();
        tre.BillingModel = new BillingModelType();
        tre.BillingModel.BillingModelID = 1;
        tre.BillingModel.BillingModelDescription = "Flat";
        tre.ID = 01;
        tre.EmployerName = "Employer3";

        AllClientData.Add(uno);
        AllClientData.Add(dos);
        AllClientData.Add(tre);

        BillingModelType one = new BillingModelType();
        one.BillingModelID = 1;
        one.BillingModelDescription = "Flat";

        BillingModelType two = new BillingModelType();
        two.BillingModelID = 2;
        two.BillingModelDescription = "Variable";

        BillingModelType three = new BillingModelType();
        three.BillingModelID = 3;
        three.BillingModelDescription = "Free";

        AllBillingModels.Add(one);
        AllBillingModels.Add(two);
        AllBillingModels.Add(three);

        InitializeComponent();
        this.DataContext = this;
    }

    private ObservableCollection<ClientRate> _allClientData;
    public ObservableCollection<ClientRate> AllClientData
    {
        get { return _allClientData; }
        set
        {
            if (_allClientData != value)
            {
                _allClientData = value;
                FirePropertyChanged("AllClientData");
            }
        }
    }

    private ClientRate _selectedClient;
    /// <summary>
    /// Gets/Sets Global SelectedClient object
    /// </summary>
    public ClientRate SelectedClient
    {
        get { return _selectedClient; }
        set
        {
            if (_selectedClient != value)
            {
                _selectedClient = value;
                FirePropertyChanged("SelectedClient");
            }
        }
    }

    //private BillingModelType _selectedBillingModel;
    //public BillingModelType SelectedBillingModel
    //{
    //    get
    //    {
    //        return _selectedBillingModel;
    //    }
    //    set
    //    {
    //        if (_selectedBillingModel != value)
    //        {
    //            _selectedBillingModel = value;
    //            FirePropertyChanged("SelectedBillingModel");
    //        }
    //    }
    //}

    private ObservableCollection<BillingModelType> _allBillingModels;
    /// <summary>
    /// Holds all possible billing model types 
    /// </summary>
    public ObservableCollection<BillingModelType> AllBillingModels
    {
        get { return _allBillingModels; }
        set
        {
            if (_allBillingModels != value)
            {
                _allBillingModels = value;
                FirePropertyChanged("AllBillingModels");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void FirePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));

    }
}

public class BillingModelType
{
    /// <summary>
    /// Billing Model ID
    /// </summary>
    public int? BillingModelID { get; set; }
    /// <summary>
    /// Billing Model Description
    /// </summary>
    public string BillingModelDescription { get; set; }
}

public class ClientRate : INotifyPropertyChanged
{
    /// <summary>
    /// Employer name with Employer ID in parentheses
    /// </summary>
    public string EmployerStr { get { return EmployerName + " (" + ID + ")"; } }
    /// <summary>
    /// Employer ID
    /// </summary>
    public int? ID { get; set; }
    private string _EmployerName;
    /// <summary>
    /// Employer Official Name
    /// </summary>
    public string EmployerName
    {
        get { return _EmployerName; }
        set
        {
            if (_EmployerName != value)
            {
                _EmployerName = value;
                FirePropertyChanged("EmployerName");
            }
        }
    }

    private BillingModelType _billingModel;
    /// <summary>
    /// Rate Type  ID and Description
    /// </summary>
    public BillingModelType BillingModel
    {
        get { return _billingModel; }
        set
        {
            if (_billingModel != value)
            {
                _billingModel = value;
                FirePropertyChanged("BillingModel");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void FirePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));

    }
}