DataGrid not binding (XAML + ViewModel + ObservableCollection) - wpf

Question

New to the WPF + XAML + MVVM stack so I'm sure I'm doing something basic here, but Googling hasn't helped me figure it out. I think A second set of eyes may help.
The Setup
I have a list of Objects called FilesToAdd
I have a DataGrid bound to this list
I have a drag and drop event that fires handling code
I've confirmed this works via Console.WriteLine() output.
The Goal
When an item is added to the list, I'd like the datagrid to be updated with the appropriate information that has just been added to the list.
The Problem
The list seems to be updated, but the datagrid never is.
The Code
Showing only the relevant parts.
UploaderViewModel Class
private ObservableCollection<IAddableFile> _filesToAdd;
public event PropertyChangedEventHandler PropertyChanged;
public UploaderViewModel()
{
_filesToAdd = new ObservableCollection<IAddableFile>();
}
protected virtual void OnPropertyChanged(string name)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(name));
}
}
public ObservableCollection<IAddableFile> FilesToAdd
{
get { return _filesToAdd; }
set
{
if (value != _filesToAdd)
{
_filesToAdd = value;
OnPropertyChanged("FilesToAdd");
OnPropertyChanged("FilesAreQueued");
}
}
}
public bool FilesAreQueued
{
get { return (FilesToAdd.Count > 0); }
}
public void AFileHasBeenAdded(string filepath)
{
var message = String.Format("File dropped: {0}", filepath);
Console.WriteLine(message);
var newFileInfo = new FileInfo(filepath);
if (newFileInfo.Exists && newFileInfo.Length > 0 && (!FileIsADirectory(newFileInfo))) // only add the file to the ViewModel if it's
{
FilesToAdd.Add(new FileSystemFile(newFileInfo)); //Creating our own type becaause we do additional things with it
Console.WriteLine(String.Format("File added to list: {0}", newFileInfo.FullName));
}
}
XAML Binding
<DataGrid ItemsSource="{Binding FilesToAdd}" Height="100" ScrollViewer.HorizontalScrollBarVisibility="Auto" ScrollViewer.VerticalScrollBarVisibility="Auto" MaxHeight="100" AutoGenerateColumns="False" Visibility="{Binding FilesAreQueued, Converter={StaticResource BoolToVisConverter}}">
<DataGrid.Columns>
<DataGridTextColumn Header="File Name" Binding="{Binding FileName}"/>
<DataGridTextColumn Header="Size" Binding="{Binding FileSizeInText}"/>
</DataGrid.Columns>
</DataGrid>
What am I missing? I've been looking at the pattern and I know it has to be something simple I'm not seeing due to staring at a screen for too long. :)

Answer 1

Edit: I suspect the DataGrid updates just fine but you can't see it because the FilesAreQueued property is lying.
You would need something like
FilesToAdd.CollectionChanged += (s,e) =>
OnPropertyChanged("FilesAreQueued");
As you only want to do that once (if at all, can bind to FilesToAdd.Count directly), you really should opt for a readonly collection field.
Looks fine if the DataContext of the view is actually that view-model.
Another issue could be that the class is not implementing INotifyPropertyChanged (you can have the event without actually implementing it using class : interface), this would only apply if you overwrite the FilesToAdd property with a new instance. (In general i expose collections as get-only with a readonly field.)
Might want to check for binding errors (don't think you get any for bindings to a null DataContext though).
(Also i would recommend making the OnPropertyChanged thread-safe, i.e. var handler = <event>; if (handler != null) handler();)