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How to implement Loading Incrementally (ItemAppearing) Items in ListView using MVVM in Xamarin Forms?

I am having a ListView in which items are added incrementally using ItemAppearing. I want it to implement it through my ViewModel. ItemAppearing only calls a method from View.cs hence, is there any way I could implement it in my ViewModel class.
Please note that I can load incrementally items when adding it from View.cs. I just want to load more items from ViewModel.
Here is my XAML code:
<ListView ItemsSource="{Binding JobsList}" HasUnevenRows="True"
SelectedItem="{Binding SelectedJob}" ItemAppearing="LoadMoreItems">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Label Text="{Binding Title}" />
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>

It would be best if you add (to your question) more details about what you are trying to do.
The following technique blurs the line between "what View does" and "what ViewModel does" - and "tightly couples" your View and your ViewModel - it is possible that there is a better way to approach your goal. Nevertheless, this is a useful technique to know, so I'll show it.
Details for Jason's comment "call your VM method from event handler".
Add a public method to your VM:
public class MyVM
{
public void MyMethod() {
// whatever you need to do to prepare the item.
}
}
In LoadMoreItems, call that method:
((MyVM)BindingContext).MyMethod();
Add parameters as needed.
If you need to "call back" to a method in your View, do that via an action parameter:
public void MyMethod(Action<...> action) {
...
action(...);
}
For more details, google C# passing an Action as a parameter.
There are other techniques for communicating between View and ViewModel - search for more info on that topic.

This answer will be moderately lengthy, but you will not find it anywhere else. I have tried for 2 days.
This answer is lengthy because I have demonstrated 3 things:
Binding ItemAppearing to Command and then incrementally loading items.
Selecting an Item from ListView and displaying it.
Showing animation while loading new items incrementally.
In MVVM, ViewModel is supposed to be ignorant of the View. Hence ViewModel must not know if the ListView inside the View is scrolled to the last item or whether LoadMoreItems should be called on scrolling.
We need to convert ItemAppearing Event to Command and Bind this Command to the ItemAppearing event.
For this purpose we need to install Xamarin.CommunityToolkit Nuget Package. This package is supported by .NetFoundation, Xamarin Community and Microsoft, and is authored by Microsoft. This is the official package and is necessary for most of the advanced Xamarin.Forms. Check more on Nuget.org, Download latest stable release: https://www.nuget.org/packages/Xamarin.CommunityToolkit (Install in all your projects Shared, Android, iOS, UWP, WPF, Tizen, etc)
Assume your Model:
public class Job
{
public int Id { get; set; }
public string Title { get; set; }
}
Now in your XAML
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
...
xmlns:xct="http://xamarin.com/schemas/2020/toolkit">
<StackLayout>
<RefreshView IsRefreshing="{Binding IsLoading}">
<ListView ItemsSource="{Binding JobsList}" SelectedItem="{Binding SelectedJob}">
<ListView.Behaviors>
<xct:EventToCommandBehavior EventName="ItemAppearing"
Command="{Binding LoadMoreItemsCommand}"
CommandParameter="{Binding ItemVisibilityEventArgs}"/>
</ListView.Behaviors>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label Text="{Binding Id}" />
<Label Text="{Binding Title}" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage>
In your code behind set BindingContext to instance of the ViewModel
public partial class ListPage : ContentPage
{
ListPageViewModel ListPageVM;
public JobsListPage()
{
InitializeComponent();
ListPageVM = new ListPageViewModel();
BindingContext = ListPageVM;
}
}
In Your ViewModel
public class ListPageViewModel : INotifyPropertyChanged
{
public ObservableCollection<Models.Job> JobsList
{
get { return jobsList; }
set { jobsList = value; OnPropertyChanged(nameof(JobsList)); }
}
public ICommand LoadMoreItemsCommand { get; private set; }
// Used to show Loading Animation in Refresh View
public bool IsLoading
{
get { return isLoading; }
set { isLoading = value; OnPropertyChanged(nameof(IsLoading)); }
}
public Models.Job SelectedJob
{
get { return selectedJob; }
set
{
if (value != null)
{
selectedJob = value;
var page = Application.Current.MainPage;
page.DisplayAlert("Alert", $"Selected: {selectedJob.JobTitle}", "OK");
OnPropertyChanged(nameof(SelectedJob));
}
}
}
ObservableCollection<Models.Job> jobsList;
Models.Job selectedJob;
bool isLoading;
public ListPageViewModel() // ViewModel Constructor
{
// Initialize your List
JobsList = new ObservableCollection<Models.Job>
{
new Models.Job() { Id = 0001, Title = "Product Manager" },
new Models.Job() { Id = 0002, Title = "Senior Executive" },
}
LoadMoreItemsCommand = new Command<ItemVisibilityEventArgs>(
execute: async (ItemVisibilityEventArgs args) =>
{
if ((args.Item as Models.Job).Id >= JobsList[JobsList.Count - 1].Id)
{
IsLoading = true;
for (int i = 0; i < 10; i++)
{
JobsList.Add(new Models.Job()
{
Id = JobsList.Count + 1, JobTitle = JobsList[i].Title
});
}
await System.Threading.Tasks.Task.Delay(2000); // Fake delay
IsLoading = false;
}
});
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}

Tap Gesture on List View Items

I am trying to open another view after tapping on an item in the list view.
I have tried adding a TapGestureRegonizer and even adding ViewCell with grids etc. None of these seem to work. I have added a tap gesture to a label and that seemed to work but the same does not work for list view items. This seems like a simple problem for something like list view, but there doesnt seem to be a built in functionality for this.
The Xaml:
<ListView x:Name="dataList"
ItemsSource="{Binding routeLabels}"
HasUnevenRows="True"
Grid.Row="1"
Grid.Column="0"
Grid.ColumnSpan="3">
</ListView>
The code behind:
var listviewgesture = new TapGestureRecognizer();
listviewgesture.SetBinding(TapGestureRecognizer.CommandProperty,"LoadRoutePage");
dataList.GestureRecognizers.Add(listviewgesture);
The view model:
public ICommand LoadRoutePage { get; protected set; }
public DriverDashboardViewModel(INavigation navigation,MessagDatabase database)
{
this._database = database;
this.Navigation = navigation;
this.LoadNotifications = new Command(async () => await OpenNotificationsPage());
this.LoadRoutePage = new Command(async () => await OpenRoutePage());
}
public async Task OpenRoutePage()
{
await Navigation.PushAsync(new RoutePageView());
}
Just to be clear the LoadNotifications method does work in opening a page but LoadRoutePage does not. So I know there is some level of communication between the view and viewmodel.

You should not be adding a TapGestureRecognizer to a ListView. Every cell already has events that handle tapping on them and a GestureRecognizer would probably only confuse the ListView regarding what the tap should be doing. There are a few ways to go about this.
1. SelectedItem binding
Bind a SelectedItem property to the ListView and handle your method calls in the setter of that property.
<ListView x:Name="dataList" ItemsSource="{Binding routeLabels}"
HasUnevenRows="True" Grid.Row="1" Grid.Column="0"
Grid.ColumnSpan="3" SelectedItem="{Binding SelectedItem}">
</ListView>
And in your viewmodel:
string _selectedItem;
public string SelectedItem {
get {return _selectedItem; }
set
{
_selectedItem = value;
// Additional code
}
}
2. Use the built in events ItemSelected or ItemTapped
A ListView has some events you can hook up named ItemSelected and ItemTapped. These can be caught in code-behind and can handle what you're trying to achieve.
<ListView x:Name="dataList" ItemsSource="{Binding routeLabels}"
HasUnevenRows="True" Grid.Row="1" Grid.Column="0"
Grid.ColumnSpan="3" ItemSelected="Handle_ItemSelected" ItemTapped="Handle_ItemTapped">
</ListView>
3. Use event to command binding with behaviors
Since you use viewmodels you ideally don't want these events since they're handled on the UI side. There are NuGet packages out there that can translate an event to a Command that you can handle in your viewmodel. Take a look at Corcav.Behaviors for example.
4. Create a behavior of your own
I have one I use regularly which looks like this:
public class ListViewSelectedItemBehavior : Behavior<ListView>
{
public static readonly BindableProperty CommandProperty = BindableProperty.Create(nameof(Command), typeof(ICommand), typeof(ListViewSelectedItemBehavior));
public ICommand Command
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
public ListView AssociatedObject { get; private set; }
protected override void OnAttachedTo(ListView bindable)
{
base.OnAttachedTo(bindable);
AssociatedObject = bindable;
bindable.BindingContextChanged += OnBindingContextChanged;
bindable.ItemSelected += OnListViewItemSelected;
}
protected override void OnDetachingFrom(ListView bindable)
{
base.OnDetachingFrom(bindable);
bindable.BindingContextChanged -= OnBindingContextChanged;
bindable.ItemSelected -= OnListViewItemSelected;
AssociatedObject = null;
}
private void OnBindingContextChanged(object sender, EventArgs e)
{
OnBindingContextChanged();
}
private void OnListViewItemSelected(object sender, SelectedItemChangedEventArgs e)
{
if (Command == null)
return;
if (Command.CanExecute(e.SelectedItem))
Command.Execute(e.SelectedItem);
}
protected override void OnBindingContextChanged()
{
base.OnBindingContextChanged();
BindingContext = AssociatedObject.BindingContext;
}
}
To add this to your ListView you simply add a behavior to it:
<ListView x:Name="dataList" ItemsSource="{Binding routeLabels}"
HasUnevenRows="True" Grid.Row="1" Grid.Column="0"
Grid.ColumnSpan="3">
<ListView.Behaviors>
<behaviors:ListViewSelectedItemBehavior Command="{Binding ItemSelectedCommand}" />
</ListView.Behaviors>
</ListView>
In this case ItemSelectedCommand is a Command object in your ViewModel.

Not sure if I understand you correctly but you are trying to get an event going when someone taps on anelement of a listview?
If so you don't need a recognizer you simply have to add ItemTapped in your XAML:
<ListView x:Name="dataList"
ItemsSource="{Binding routeLabels}"
HasUnevenRows="True"
Grid.Row="1"
Grid.Column="0"
ItemTapped="Name of event"
Grid.ColumnSpan="3">
</ListView>
This will generate an event for you ( just do double tab when creating the ItemTapped ) and here you can place your code

You're binding a command instead of an event to the "Tapped" event. Try something like this:
code behind:
var listviewgesture = new TapGestureRecognizer();
listviewgesture.Tapped += Handle_listViewItemTapped;
dataList.GestureRecognizers.Add(listviewgesture);
ViewModel:
private void Handle_listViewItemTapped(object sender, EventArgs e)
{
viewModel.OpenRoutePage();
}

Binding list to textbox won't update if ObservableCollection

I'm creating a custom control in WPF. I bind a List<IMyInterface> to a dependency property. This in turn binds again to a ListBox which shows all the items as expected.
I now want to bind 1 item from this list to a Textblock, so I bind the entire list to the textblock. I have a converter in this which extracts the single item I want.
It has worked fine but for a few reasons, I want to use ObservableCollection instead of List
Oddly, when I change a value in my ObservabaleCollection at run time, the value is shown in the ListBox (success) but not in my textblock. The converter is not even hit!
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
this.Errors = new ObservableCollection<IEventDetail>();
this.Errors.CollectionChanged += Errors_CollectionChanged;
var bw = new BackgroundWorker();
bw.DoWork += ((o, e) =>
{
System.Threading.Thread.Sleep(1500);
Dispatcher.Invoke(() =>
{
this.Errors.Add(new MyEvents("example of some detail", "Failed title"));
});
System.Threading.Thread.Sleep(2500);
Dispatcher.Invoke(() =>
{
this.Errors.Add(new MyEvents("Another example", "Failed title 2"));
});
});
bw.RunWorkerAsync();//background worker for testing/debugging only
}
private void Errors_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
OnPropertyChanged("Errors");
}
private ObservableCollection<IEventDetail> _errors;
public ObservableCollection<IEventDetail> Errors
{
get
{
return this._errors;
}
set
{
this._errors = value;
OnPropertyChanged("Errors");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged == null)
return;
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
And the xaml is simply
<local:Notify Events="{Binding Errors}" DockPanel.Dock="Right"/>
As you can see, I've tried to use the CollectionChanged event to then force fire the INotifyPropertyChanged, but it's firing in my Converter yet the ListBox is updating fine (so I know the binding is fine)
This is the UserControls xaml
<TextBlock Text="{Binding Path=Events, RelativeSource={RelativeSource AncestorLevel=1, AncestorType=UserControl}, Mode=Default, Converter={StaticResource MostRecentConverter}}" Grid.Row="0" />
<ListBox ItemsSource="{Binding Path=Events, RelativeSource={RelativeSource AncestorLevel=1,AncestorType=UserControl}, Mode=Default}" Grid.Row="1">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding EventTitle}" Style="{StaticResource txtBckRed}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Do I need to do something else?

As mentioned in the comments TextBlock it bound only to Events property change (not its items) so it won't trigger unless new instance of collection is created. Reacting to INotifyCollectionChanged is characteristic to ItemsSource property.
Solution 1
Leave everything as it is at the moment just give TextBlock some name
<TextBlock Text="{Binding ...}" x:Name="myTextBlock"/>
and subscribe to CollectionChanged event inside your UserControl where you manually force binding target to update
public partial class MyUserControl : UserControl
{
public static readonly DependencyProperty EventsProperty =
DependencyProperty.Register("Events",
typeof(IEnumerable),
typeof(MyUserControl),
new PropertyMetadata(EventsPropertyChanged));
private static void EventsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((MyUserControl)d).EventsPropertyChanged(e);
}
private void EventsPropertyChanged(DependencyPropertyChangedEventArgs args)
{
var newCollection = args.NewValue as INotifyCollectionChanged;
if (newCollection != null)
newCollection.CollectionChanged += (s, e) => myTextBlock.GetBindingExpression(TextBlock.TextProperty).UpdateTarget();
}
public IEnumerable Events
{
get { return (IEnumerable)GetValue(EventsProperty); }
set { SetValue(EventsProperty, value); }
}
}
Solution 2
Create your own collection class inherited from ObservableCollection<T> with custom property that would do what your converter does
public class MyObservableCollection<T> : ObservableCollection<T>
{
private string _convertedText;
protected override void OnCollectionChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
base.OnCollectionChanged(e);
this.ConvertedText = ...; // <- do here what your IValueConverter does
}
public string ConvertedText
{
get { return _convertedText; }
private set
{
_convertedText = value;
OnPropertyChanged(new PropertyChangedEventArgs("ConvertedText"));
}
}
}
and bind TextBlock.Text to Events.ConvertedText property instead, without need for converter

Binding ObservableCollection in viewmodel to listbox

I'm very new to MVVM and bindings and I'm trying to learn to work with it.
I run into the problem of binding my viewmodel to the view in particular binding an observable collection to a listbox.
this is what my viewmodel looks like:
namespace MyProject
{
using Model;
public class NetworkViewModel: INotifyPropertyChanged
{
private ObservableCollection<Person> _networkList1 = new ObservableCollection<Person>();
public ObservableCollection<Person> NetworkList1 //Binds with the listbox
{
get { return _networkList1; }
set { _networkList1 = value; RaisePropertyChanged("_networkList1"); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
var handler = this.PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public NetworkViewModel()
{
_networkList1 = new ObservableCollection<Person>()
{
new Person(){FirstName="John", LastName="Doe"},
new Person(){FirstName="Andy" , LastName="Boo"}
};
}
}
in the view I have
namespace MyProject
{
public partial class Networking : Window
{
public Networking()
{
InitializeComponent();
this.DataContext = new NetworkViewModel();
lb1.ItemsSource = _networkList1;
}
}
}
and in the XAML I have
<ListBox x:Name="lb1" HorizontalAlignment="Left" ItemsSource="{Binding NetworkList1}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock >
<Run Text="{Binding Path=FirstName}"/>
<Run Text="{Binding Path=LastName}"/>
</TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>

It seems like you might have a typo in your view model.
RaisePropertyChanged("_networkList1");
You want to raise the property changed notification for the public property not the private variable.
RaisePropertyChanged("NetworkList1");
This might be preventing your view from updating properly.

In addition to Gaurav answer, if _networkList1 is a private field in your NetworkViewModel class, how is it possible to get access to it in Networking window? I mean what's the meaning of the following line?
lb1.ItemsSource = _networkList1;
when you define a Property (NetworkList1), you have to use it in order to get advantages of its features (e.g. to get RaisePropertyChanged working). Otherwise what's the point, you could have just defined a field (_networklist1). So changing
_networkList1 = new ObservableCollection<Person>()
to
NetworkList1 = new ObservableCollection<Person>()
results in actually setting NetworkList1 and therefore RaisePropertyChanged("NetworkList1") to be fired. (however if you want to just show data in a your listbox this is unnecessary)
and if i'm getting it right, changing this:
public partial class Networking : Window
{
public Networking()
{
InitializeComponent();
this.DataContext = new NetworkViewModel();
lb1.ItemsSource = _networkList1;
}
}
to
public partial class Networking : Window
{
public NetworkViewModel MyViewModel { get; set; }
public Networking()
{
InitializeComponent();
MyViewModel = new NetworkViewModel();
this.DataContext = MyViewModel;
}
}
should get your binding to work.
*Note that when you set DataContext to NetworkViewModel, then the binding in
<ListBox x:Name="lb1" HorizontalAlignment="Left" ItemsSource="{Binding NetworkList1}">
works, because NetworkList1 is a Property of NetworkViewModel.

Do not call RaisePropertyChanged() method on ObservableCollection<T>, for god's sake. This is a common mistake in a majority of cases (however, there are cases, where you need to reset ObservableCollection<T> using new keyword, but they are kinda rare).
This is a special type of collection which notifies UI internally about all the changes of its content (like add, remove etc.). What you need is to set the collection using new keyword once in a lifetime of your ViewModel, and then manipulate your items via Add(T item), Remove(T item), Clear() methods etc.
and UI will get notified about it and updated automatically.

WPF ComboBox Binding works if previous record had no matching item in the ItemsSource collection and fails if it did

I have the following WPF Combobox:
<Window.Resources>
<CollectionViewSource x:Key="performanceItemsource" Source="{Binding Path=SelectedReport.Performances}" >
<CollectionViewSource.SortDescriptions>
<scm:SortDescription PropertyName="Name"/>
</CollectionViewSource.SortDescriptions>
</CollectionViewSource>
</Window.Resources>
...
<ComboBox Name="cbxPlanPerf" Grid.ColumnSpan="2"
SelectedValuePath="MSDPortfolioID" DisplayMemberPath="Name"
SelectedValue="{Binding Path=PlanPerfID}"
ItemsSource="{Binding Source={StaticResource performanceItemsource}}"/>
The Source for the CollectionViewSource is:
public List<MSDExportProxy> Performances
{
get
{
if (Portfolio != null)
{
return (from a in Portfolio.Accounts where a.MSDPortfolioID != null select new MSDExportProxy(a))
.Concat<MSDExportProxy>(from g in Portfolio.Groups where g.MSDPortfolioID != null select new MSDExportProxy(g))
.Concat<MSDExportProxy>(from p in new[] { Portfolio } where p.MSDPortfolioID != null select new MSDExportProxy(p))
.ToList<MSDExportProxy>();
}
return new List<MSDExportProxy>();
}
}
The bound property PlanPerfID is a string.
I move between records using a ListBox control. The ComboBox works fine if the previous record had no items in its ComboBox.ItemsSource. If there were any items in the previous record's ComboBox.ItemsSource then the new record won't find its matching item in the ItemsSource collection. I've tried setting the ItemsSource in both XAML and the code-behind, but nothing changes this odd behavior. How can I get this darn thing to work?

Try using ICollectionViews in combination with IsSynchronizedWithCurrentItem property when handling lists / ObservableCollection in Xaml. The ICollectionView in the viewmodel can handle all the things needed, e.g. sorting, filtering, keeping track of selections and states.
Xaml:
<Window x:Class="ComboBoxBinding.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">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<ListBox Grid.Column="0"
ItemsSource="{Binding Reports}"
DisplayMemberPath="Name"
IsSynchronizedWithCurrentItem="True" />
<ComboBox Grid.Column="1"
ItemsSource="{Binding CurrentReport.Performances}"
DisplayMemberPath="Name"
IsSynchronizedWithCurrentItem="True" />
</Grid>
</Window>
ViewModel:
public class ViewModel : INotifyPropertyChanged
{
private readonly IReportService _reportService;
private ObservableCollection<ReportViewModel> _reports = new ObservableCollection<ReportViewModel>();
private PerformanceViewModel _currentPerformance;
private ReportViewModel _currentReport;
public ObservableCollection<ReportViewModel> Reports
{
get { return _reports; }
set { _reports = value; OnPropertyChanged("Reports");}
}
public ReportViewModel CurrentReport
{
get { return _currentReport; }
set { _currentReport = value; OnPropertyChanged("CurrentReport");}
}
public PerformanceViewModel CurrentPerformance
{
get { return _currentPerformance; }
set { _currentPerformance = value; OnPropertyChanged("CurrentPerformance");}
}
public ICollectionView ReportsView { get; private set; }
public ICollectionView PerformancesView { get; private set; }
public ViewModel(IReportService reportService)
{
if (reportService == null) throw new ArgumentNullException("reportService");
_reportService = reportService;
var reports = _reportService.GetData();
Reports = new ObservableCollection<ReportViewModel>(reports);
ReportsView = CollectionViewSource.GetDefaultView(Reports);
ReportsView.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));
ReportsView.CurrentChanged += OnReportsChanged;
ReportsView.MoveCurrentToFirst();
}
private void OnReportsChanged(object sender, EventArgs e)
{
var selectedReport = ReportsView.CurrentItem as ReportViewModel;
if (selectedReport == null) return;
CurrentReport = selectedReport;
if(PerformancesView != null)
{
PerformancesView.CurrentChanged -= OnPerformancesChanged;
}
PerformancesView = CollectionViewSource.GetDefaultView(CurrentReport.Performances);
PerformancesView.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));
PerformancesView.CurrentChanged += OnPerformancesChanged;
PerformancesView.MoveCurrentToFirst();
}
private void OnPerformancesChanged(object sender, EventArgs e)
{
var selectedperformance = PerformancesView.CurrentItem as PerformanceViewModel;
if (selectedperformance == null) return;
CurrentPerformance = selectedperformance;
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}

I found a quick and dirty solution to my problem. I just happen to have a public NotifyPropertyChanged() method on my Report entity and I discovered that if I called SelectedReport.NotifyPropertyChanged("PlanPerfID") in the Report ListBox's SelectionChanged event that it was enough of a jolt to get the ComboBox to re-evaluate and find its matching item in the ItemsSource. Yeah, it's KLUGE...
UPDATE: I also wound up needing to add SelectedReport.NotifyPropertyChanged("Performances") for some situations...
UPDATE 2: Okay, turns out the above wasn't bullet proof and I ran across a situation that broke it so I had to come up with a better workaround:
Altered the SelectedReport property in the Window's code-behind, adding a private flag (_settingCombos) to keep the Binding from screwing up the bound values until the dust has settled from changin the ItemSource:
private bool _settingCombos = false;
private Report _SelectedReport;
public Report SelectedReport
{
get { return _SelectedReport; }
set
{
_settingCombos = true;
_SelectedReport = value;
NotifyPropertyChanged("SelectedReport");
}
}
Created a proxy to bind to in the Window code-behind that will refuse to update the property's value if the _settingCombos flag is true:
public string PlanPerfID_Proxy
{
get { return SelectedReport.PlanPerfID; }
set
{
if (!_settingCombos)
{
SelectedReport.PlanPerfID = value;
NotifyPropertyChanged("PlanPerfID_Proxy");
}
}
}
Added an extra Notification in the Report ListBox's SelectionChanged event along with code to reset the _settingCombos flag back to false:
private void lbxReports_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
//KLUGE: Couldn't get the ComboBoxes associated with these properties to work right
//this forces them to re-evaluate after the Report has loaded
if (SelectedReport != null)
{
NotifyPropertyChanged("PlanPerfID_Proxy");
_settingCombos = false;
}
}
Bound the ComboBox to the PlanPerfID_Proxy property (instead of directly to the SelectedReport.PlanPerfID property.
Wow, what a hassle! I think that this is simply a case of .NET's binding logic getting confused by the dynamic nature of the ComboBox.ItemSource, but this seems to have fixed it. Hope it helps someone else.