WPF: Entity Framework MVVM Walk Through 2 Andy ONeills example

Question

I have learnt a lot from Andy O'Neill's WPF: Entity Framework MVVM Walk Through 2 example as I learn WPF and MVVM etc. Generally though I always seem to struggle on comboboxes and getting the ItemsSource, SelectedValue and SelectedValuePath set up correctly to successfully show data in the combobox. The Binding is really tricky in combination with the particular comboxbox control design. In Andys example I was trying to put a combobox inside an ItemsControl thats inside a ContentControl (Popup) thats inside a grid on a UserControl. I cannot get the data from MyObservableCollection to show in the ItemsSource. I have tried all manner of versions of comboc control construction and Binding including {Binding DataContext.MyObservableCollection, Mode=TwoWay, RelativeSource={RelativeSource AncestorType=UserControl} , RelativeSource={RelativeSource AncestorType={x:Type local:UserControl}} and replacing UserControl with the ViewModels , and using FindAncestor etc. The DataContext is set to the ViewModel where the observable collection is and its got data in it, but seems cant get binding to work.

Any tips to look at for this type of situation would be greatly appreciated or even an answer from the great man himself Mr Andy O'Neill (anonymous userONeill) . wow imagine that

thanks
Scott

Answer 1

Hi Scott,
in following demo you can see how to bind ComboBoxColumn in DataGrid in UserControl.

XAML MainWindow:

<Window x:Class="Window064"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:WpfApp1.WpfApp064"  
        xmlns:uc="clr-namespace:WpfControlLibrary1;assembly=WpfControlLibrary1"  
        mc:Ignorable="d"  
        Title="Demo ComboBox in UserControl" Height="450" Width="800">  
  <Window.DataContext>  
    <local:ViewModel/>  
  </Window.DataContext>  
  <Grid>  
    <uc:Window064UC1/>  
  </Grid>  
</Window>  

ViewModel as DataContext in MainWindow (and UserControl), View property for rows in DataGrid, MasterList as Lookup values for ItemsSource in DataGridComboBoxColumn, LoadDemoData for loading data (e.g. EF).

Imports System.Collections.ObjectModel  
Imports System.ComponentModel  
  
Namespace WpfApp064  
  
  Public Class ViewModel  
  
    Public Sub New()  
      LoadDemoData  
    End Sub  
  
    Private cvsChild As New CollectionViewSource  
    Private colChild As New ObservableCollection(Of Data)  
    Public ReadOnly Property View As ICollectionView  
      Get  
        Return cvsChild.View  
      End Get  
    End Property  
  
    Private colMaster As New ObservableCollection(Of Master)  
    Public ReadOnly Property MasterList As ObservableCollection(Of Master)  
      Get  
        Return colMaster  
      End Get  
    End Property  
  
    Private Sub LoadDemoData()  
      Dim rnd As New Random  
      For i = 1 To 10  
        colMaster.Add(New Master With {.ID = i, .MasterInfo = $"Master {i}"})  
      Next  
      For i = 1 To 100  
        colChild.Add(New Data With {.ID = i, .Info = $"Row {i}", .FKMaster = rnd.Next(1, 11)})  
      Next  
      cvsChild.Source = colChild  
    End Sub  
  End Class  
  
  Public Class Data  
    Public Property ID As Integer  
    Public Property FKMaster As Integer  
    Public Property Info As String  
  End Class  
  
  Public Class Master  
    Public Property ID As Integer  
    Public Property MasterInfo As String  
  End Class  
  
End Namespace  

XAML UserControl (no CodeBehind)

<UserControl x:Class="Window064UC1"  
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"   
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"   
             xmlns:local="clr-namespace:WpfControlLibrary1"  
             mc:Ignorable="d"   
             d:DesignHeight="450" d:DesignWidth="800">  
  <Grid>  
    <Grid.Resources>  
      <CollectionViewSource x:Key="ItemsCVS" Source="{Binding MasterList}" />  
    </Grid.Resources>  
    <DataGrid ItemsSource="{Binding View}" AutoGenerateColumns="False">  
      <DataGrid.Columns>  
        <DataGridTextColumn Header="ID" Binding="{Binding ID}"/>  
        <DataGridTextColumn Header="Info" Binding="{Binding Info}"/>  
        <DataGridComboBoxColumn Header="Lookup"  
                                ItemsSource="{Binding Source={StaticResource ItemsCVS}}"  
                                DisplayMemberPath="MasterInfo"  
                                SelectedValuePath="ID"  
                                SelectedValueBinding="{Binding FKMaster}"/>  
      </DataGrid.Columns>  
    </DataGrid>  
  </Grid>  
</UserControl>  

Result:

Answer 2

Finally solved it. Went back and carefully looked at how it worked more closely and realised I was working with collection of row VMs as apposed to the observable collection of the class derived from the entity model so filled the combobox with a collection of these and referenced via "The Entity" reference.

Whilst its great to use other peoples code to learn from you do have to really LEARN it as you start to modify it to suit your purpose.

thanks gents for the help.