Databinding not updating ListBox completely - wpf

Question

I'm using the MVVM pattern and have a databound Listbox that isn't updating completely.
There is a modelview that contains an Observable collection of Machines which is bound to the list:
<ListBox Name="MachinesList"
Height="300"
Width="290"
DataContext="{Binding Path=AllMachines}"
SelectionMode="Single"
ItemsSource="{Binding}" SelectionChanged="MachinesList_SelectionChanged"
HorizontalAlignment="Right"
>
The collection AllMachines Contains an observable collection of MachineModelViews which are in turn bound to a MachineView that presents the name and location of the machine:
<StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
<Label Name="NameLabel" Content="{Binding Path=Name}" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Width="50" />
<Label Content="Location:" Width="120"
HorizontalAlignment="Right"
HorizontalContentAlignment="Center"
VerticalContentAlignment="Center"
Target="{Binding ElementName=locationLabel}"
/>
<Label Content="{Binding Path=Location.Name}" Name="locationLabel" HorizontalContentAlignment="Center" Width="60"/>
</StackPanel>
The problem:
When values are added to the collection things update okay. When a machine is deleted however only the Label bound to Location.Name updates the other two remain in the listbox. I've confirmed that the collection is actually updating and removing the MachineModelView Correctly but some how the label with it's name and the "label label" with "Location:" continues to exist until the application is restarted:
before:
after delete:
after app restart:
The delete button calls a command which removes the item from the private member that backs the AllMachines property and from the repository (which ultimately plugs into a database via Entity Framework):
RelayCommand _deleteCommand;
public ICommand DeleteCommand
{
get
{
if (_deleteCommand == null)
{
_deleteCommand = new RelayCommand(
param => this.Delete(),
null
);
}
return _deleteCommand;
}
}
void Delete()
{
if (_selectedMachine != null && _machineRepository.GetMachines().
Where(i => i.Name == _selectedMachine.Name).Count() > 0)
{
_machineRepository.RemoveMachine(_machineRepository.GetMachines().
Where(i => i.Name == _selectedMachine.Name).First());
_allMachines.Remove(_selectedMachine);
}
}
Note: There can only be one item with a name in AllMachines (this is handled by the add logic in the repository and command itself) so removing the "First" one should be fine.
The AllMachines property:
public ObservableCollection<MachineViewModel> AllMachines
{
get
{
if(_allMachines == null)
{
List<MachineViewModel> all = (from mach in _machineRepository.GetMachines()
select new MachineViewModel(mach, _machineRepository)).ToList();
_allMachines = new ObservableCollection<MachineViewModel>(all);
}
return _allMachines;
}
private set
{
_allMachines = value;
}
}
The selection changed event handler:
private void MachinesList_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (e.AddedItems.Count > 0 && e.AddedItems[0] is MachineViewModel)
((MachinesViewModel)this.DataContext).SelectedMachine = (MachineViewModel)e.AddedItems[0];
}

Answer 1

If 'AllMachines is your actual observable collection, I would bind the itemssource to that instead of binding it to ur datacontext, and then bind ur viewmodel as your datacontext. It may also be helpful to call the updatesourcetrigger after your itemssource bind.
DataContext="{Binding Path=YourViewModel}"
SelectionMode="Single"
ItemsSource="{Binding AllMachines, UpdateSourceTrigger="PropertyChanged"}"
And you can use that updatesourcetrigger on some of your labels as well where you are binding. Other than that, you xaml looks ok, hard for anyone to really say until they see everything.

Answer 2

_machineRepository.RemoveMachine(_machineRepository.GetMachines().
Where(i => i.Name == _selectedMachine.Name).First());
AllMachines.Remove(_selectedMachine);
Instead of field _allMachines.Remove remove directly from the property AllMachines like
AllMachines.Remove
I hope this will help.

Answer 3

if you code the way you said here, then all should work. pls post the missing code pieces:
your AllMaschines Property
your MachinesList_SelectionChanged event <-- when doing MVVM you almost not need this
pls debug your Delete() method just to be sure that: _allMachines.Remove(_selectedMachine); is hit and the machine is really removed from your collection.

Answer 4

I found my problem, really stupid: I have an event that fires when the repository updates. Before I only had an add command and I was adding the ability to delete when this problem came up. Turns out the event was being handled by the MachinesModelView to update it's internal variable that is the source for the AllMachines property:
void OnMachineAddedToRepository(object sender, MachineAddedOrRemovedEventArgs e)
{
var viewModel = new MachineViewModel(e.NewMachine, _machineRepository);
this.AllMachines.Add(viewModel);
}
I modified the event arguments to toggle between add and delete but forgot to update the event handler. Now it does work:
void OnMachineAddedOrRemovedFromRepository(object sender, MachineAddedOrRemovedEventArgs e)
{
if (e.Added)
{
var viewModel = new MachineViewModel(e.NewMachine, _machineRepository);
this.AllMachines.Add(viewModel);
}
else if (AllMachines.Where(i => i.Name == e.NewMachine.Name).Count() > 0)
AllMachines.Remove(AllMachines.Where(i => i.Name == e.NewMachine.Name).First());
}
What made this so hard to track down is that the extra item only lived very briefly until the AllMachines.Remove part of the Delete command ran. So checking the pre-delete count, and the post delete count looked right it was the guts in the middle when the item is being deleted from the repository that fired off an event that added the item back and left it in this weird state. Kind of odd that it consistently only had the location part of the MachineModelView floating around. I now just let the event handler add or remove the items from the _allMachines variable and don't touch it explicitly in the delete command (the delete command just deletes it from the repository and lets the UI variables catch up in the fraction of a second it takes for the event to trigger). Thanks a bunch guys for your help.