I have a simple MVVM project with development time data that works great with master data and a list with user controls for each of the child elements. However, when I create instances of classes at runtime, the main data is displayed, however, the child data is not displayed (but the list has the correct number of elements, however, they do not have data displayed in text boxes).
I noticed that the constructor in Sport received many times, compared to what I expected (for example, at runtime, I expected it to be called only twice, but it seems to be called more than).
I have a Person and Sport class. Everyone can love several sports and have a favorite team. I have personViewModel and sportViewModel that inherit from viewModelBase.
Here is my VB.net code
Imports System.Collections.ObjectModel Public Class Person Public Property Forename As String Public Property Surname As String Public Sports As New ObservableCollection(Of Sport) End Class Public Class Sport Public Sub New() Debug.WriteLine("test") End Sub Public Property SportName As String Public Property FavouriteProfessionalTeam As String End Class Imports System.Collections.ObjectModel Namespace ViewModel Public Class PersonViewModel Inherits ViewModel.ViewModelBase Public Property Person1 As Person Public Property SportViewModels As New ObservableCollection(Of SportViewModel) Public Sub New() LoadData() End Sub ''' <summary> ''' Loads the data for the application. ''' </summary> Private Sub LoadData() If IsInDesignModeStatic Then LoadDesignData() Else End If End Sub ''' <summary> ''' Loads temporary data for use in the designer. ''' </summary> Private Sub LoadDesignData() Person1 = New Person Person1.Forename = "Mickey Run Time" Person1.Surname = "Mouse Run Time" Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Man Utd", .SportName = "Soccer"}) Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Barcelona", .SportName = "Spanish Soccer"}) Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Ulster", .SportName = "Rugby"}) For Each sport1 In Person1.Sports Dim sportVm As New SportViewModel With {.Sport1 = sport1} SportViewModels.Add(sportVm) Next End Sub End Class End Namespace Namespace ViewModel Public Class SportViewModel Inherits ViewModel.ViewModelBase Public Property Sport1 As New Sport Public Property Person1 As Person Public Sub New() LoadData() End Sub ''' <summary> ''' Loads the data for the application. ''' </summary> Private Sub LoadData() If IsInDesignModeStatic Then LoadDesignData() Else ' Debug.WriteLine(Sport1.SportName) ' Load the student data asynchronously 'StudentContextInstance = New StudentContext 'Dim loadop = ' StudentContextInstance.Load(StudentContextInstance. ' GetStudentsQuery(), ' AddressOf OnStudentsLoaded, Nothing) End If End Sub ''' <summary> ''' Loads temporary data for use in the designer. ''' </summary> Private Sub LoadDesignData() Sport1 = New Sport With {.SportName = "Design Time Name", .FavouriteProfessionalTeam = "Design Time Team"} End Sub End Class End Namespace Imports System.ComponentModel Namespace ViewModel Public Class ViewModelBase Implements INotifyPropertyChanged Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged Private Shared _isInDesignMode As Boolean? Public Shared ReadOnly Property IsInDesignModeStatic As Boolean Get If Not _IsInDesignMode.HasValue Then _IsInDesignMode = DesignerProperties.GetIsInDesignMode(New DependencyObject) End If Return _IsInDesignMode.Value End Get End Property Protected Sub OnPropertyChanged(ByVal propertyName As String) ' Send an event notification that the property changed ' This allows the UI to know when one of the items changes If Not String.IsNullOrEmpty(propertyName) Then RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName)) End If End Sub End Class End Namespace
Here is the code for my wain window that sets the MVVM to display Imports System.Collections.ObjectModel Import WpfApplicationMVVMTest.ViewModel
Class MainWindow Public Property Person1 As Person Public Property SportViewModels As New ObservableCollection(Of SportViewModel) Private Sub Button_Click_1(sender As Object, e As RoutedEventArgs) Dim wndPerson As New PersonWindow Person1 = New Person Person1.Forename = "Donald" Person1.Surname = "Duck" Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Man Utd", .SportName = "Soccer"}) Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Barcelona", .SportName = "Spanish Soccer"}) For Each sport1 In Person1.Sports Dim sportVm As New SportViewModel With {.Sport1 = sport1} SportViewModels.Add(sportVm) Next Dim vm As New ViewModel.PersonViewModel vm.SportViewModels = SportViewModels vm.Person1 = Person1 wndPerson.DataContext = vm wndPerson.Show() End Sub End Class
Here is the XAML code
<Window 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:ViewModel="clr-namespace:WpfApplicationMVVMTest.ViewModel" xmlns:View="clr-namespace:WpfApplicationMVVMTest" mc:Ignorable="d" x:Class="PersonWindow" Title="PersonWindow" Height="1114.8" Width="542"> <Window.Resources></Window.Resources> <Window.DataContext> <ViewModel:PersonViewModel /> </Window.DataContext> <Grid> <Grid x:Name="Grid1" HorizontalAlignment="Left" Margin="41,39,0,0" VerticalAlignment="Top"> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="Auto"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> </Grid.RowDefinitions> <Label Content="Forename:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="0" VerticalAlignment="Center"/> <TextBox x:Name="ForenameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="0" Text="{Binding Person1.Forename, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/> <Label Content="Surname:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="1" VerticalAlignment="Center"/> <TextBox x:Name="SurnameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="1" Text="{Binding Person1.Surname, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/> </Grid> <ListBox Margin="41,108,59,753" ItemsSource="{Binding Path=SportViewModels}" > <ListBox.ItemTemplate> <DataTemplate> <View:SportUserControl DataContext="{Binding}" Margin="5"/> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </Grid> </Window> <UserControl 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:ViewModel="clr-namespace:WpfApplicationMVVMTest.ViewModel" x:Class="SportUserControl" mc:Ignorable="d" d:DesignHeight="600" d:DesignWidth="600"> <UserControl.Resources></UserControl.Resources> <UserControl.DataContext> <ViewModel:SportViewModel /> </UserControl.DataContext> <Grid> <Grid x:Name="Grid1" HorizontalAlignment="Left" Margin="31,26,0,0" VerticalAlignment="Top"> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="Auto"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="Auto"/> </Grid.RowDefinitions> <Label Content="Favourite Professional Team:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="0" VerticalAlignment="Center"/> <TextBox x:Name="FavouriteProfessionalTeamTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="0" Text="{Binding Sport1.FavouriteProfessionalTeam, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/> <Label Content="Sport Name:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="1" VerticalAlignment="Center"/> <TextBox x:Name="SportNameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="1" Text="{Binding Sport1.SportName, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/> </Grid> </Grid> </UserControl>
Here is my design time image with 3 sports shown (according to my load design time data). 
Here is my run-time window with two sports (although they don’t have data - that’s the problem). 