WPF & Prism 4.1 Garbage Collection / Memory Issues - wpf

Question

I built a Prism application using WPF, .Net 4, Prism 4.1, and Unity. I'm using a DirectoryModuleCatalog to find modules at runtime. My views are displayed in a TabControl (MainRegion). When I remove a view from the region, the view and viewmodel remain in memory and never get garbage collected - the tabitem is removed. After many hours searching, I cannot figure out what I'm doing wrong.
Here's my bootstrapper:
public class Bootstrapper : UnityBootstrapper
{
protected override void InitializeShell()
{
base.InitializeShell();
App.Current.MainWindow = (Window)Shell;
App.Current.MainWindow.Show();
}
protected override DependencyObject CreateShell()
{
var shell = new Shell();
return shell;
}
protected override IModuleCatalog CreateModuleCatalog()
{
return new DirectoryModuleCatalog() { ModulePath = #".\Modules" };
}
}
Here's my module:
[Module(ModuleName = "ModuleA")]
public class Module : IModule
{
private IRegionManager _regionManager;
public Module(IRegionManager regionManager)
{
_regionManager = regionManager;
}
public void Initialize()
{
var view = new UserControl1();
//_regionManager.RegisterViewWithRegion("MainRegion", typeof(UserControl1));
_regionManager.Regions["MainRegion"].Add(view, "ModuleA");
_regionManager.Regions["MainRegion"].Activate(view);
}
}
And heres the viewmodel for my view that gets added to the region:
public class ViewModel
{
public DelegateCommand RemoveView { get; set; }
public ViewModel()
{
RemoveView = new DelegateCommand(() =>
{
var regionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
var view = regionManager.Regions["MainRegion"].GetView("ModuleA");
regionManager.Regions["MainRegion"].Deactivate(view);
regionManager.Regions["MainRegion"].Remove(view);
});
}
}
And here's the code behind for the view:
public partial class UserControl1 : UserControl
{
public UserControl1()
{
InitializeComponent();
this.DataContext = new ViewModel();
}
}
I've read that it could be because I'm instantiating the view in the module or perhaps the viewmodel in the view? When I use Red Gate Memory Profiler, and remove the view via the DelegateCommand, the view and viewmodel are both flagged as not being able to be garbage collected. Where is the reference that I'm not properly cutting?
Heres the retention graph from Ants: https://docs.google.com/file/d/0B4XjO9pUQxBXbGFHS1luNUtyOTg/edit?usp=sharing
Here's a test solution showing the issue.
Also, I posted the question on CodePlex as well.

Answer 1

It looks like you have a binding reference to it still in your retention graph.
Read and understand the following:
A memory leak may occur when you use data binding in Windows Presentation Foundation
I think it may be your problem, but you didn't show your actual bindings.

Answer 2

Finally found the root cause of my problem....
In our Shell.xaml we were binding IsDefault in one of our buttons to a PasswordBox's IsKeyboardFocused:
<Button Style="{DynamicResource RedSubmitButtonStyle}" IsDefault="{Binding ElementName=passwordBox1, Path=IsKeyboardFocused}" Command="{Binding LoginCommand}" Content="Login" Height="23" HorizontalAlignment="Left" Margin="145,86,0,0" Name="button1" VerticalAlignment="Top" Width="75" />
IsKeyboardFocused, is a dependency property according to MSDN - so should be good on that end.
It was related to the attached property we had on the Password box that allows us to bind to the Password entered. The focus was remaining on that password box even after we hid the ChildWindow (from WPF toolkit extended). So instead of using IsDefault, I added a keydown event to the PasswordBox and if it was Key.Enter, I would change the focused UI control and log the person into the program.
Here's the full contents of our Shell.xaml file
<Grid x:Name="MainGrid" core:SharedResourceDictionary.MergedDictionaries="TabControlThemes;MenuThemes;ButtonThemes;DataGridThemes;TreeViewThemes;ComboBoxThemes;ListBoxThemes;GroupBoxThemes;ToggleSwitchThemes">
<DockPanel>
<ContentControl x:Name="menuContent" DockPanel.Dock="Top" prism:RegionManager.RegionName="MenuRegion" />
<ContentControl DockPanel.Dock="Bottom" prism:RegionManager.RegionName="FooterRegion" />
<ContentControl DockPanel.Dock="Top" prism:RegionManager.RegionName="MainContentRegion" />
</DockPanel>
<StackPanel Orientation="Horizontal" Panel.ZIndex="4" HorizontalAlignment="Right" VerticalAlignment="Top">
<Button Visibility="{Binding IsFullScreenToggleVisible, Converter={StaticResource visConv}}" Command="{Binding ToggleFullScreen}" Height="50" Name="button4" Width="70" HorizontalAlignment="Right" Margin="0,10,10,0" VerticalAlignment="Top">
<Button.Content>
<TextBlock FontSize="12" FontWeight="Bold" TextWrapping="Wrap" TextAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Center" Text=" Toggle Full Screen" />
</Button.Content>
</Button>
<Button Visibility="{Binding IsAppCloseButtonVisible, Converter={StaticResource visConv}}" Command="{Binding ShutdownApplication}" Height="50" Name="button3" Width="50" HorizontalAlignment="Right" Margin="0,10,10,0" VerticalAlignment="Top">
<Button.Content>
<Image Source="..\Graphics\close.png" Name="image1" />
</Button.Content>
</Button>
</StackPanel>
<xctk:ChildWindow Name="loginChildWindow" Panel.ZIndex="3" CloseButtonVisibility="Collapsed" FocusedElement="{Binding ElementName=usernameTextBox}" WindowStartupLocation="Center" WindowState="{Binding IsVisible, Mode=TwoWay, Converter={StaticResource boolConverter}}" IsModal="True" OverlayOpacity="1" Caption="Pioneer Login" Height="164" Width="261">
<xctk:ChildWindow.OverlayBrush>
<ImageBrush Stretch="None" Viewport="0,0,46,29" ViewportUnits="Absolute" ImageSource="../Graphics/escheresque.png" TileMode="Tile" />
</xctk:ChildWindow.OverlayBrush>
<xctk:BusyIndicator IsBusy="{Binding IsLoginBusy}" BusyContent="Authenticating...">
<Grid>
<TextBox GotFocus="usernameTextBox_GotFocus" Text="{Binding Username, UpdateSourceTrigger=PropertyChanged}" Height="23" HorizontalAlignment="Left" Margin="99,20,0,0" Name="usernameTextBox" VerticalAlignment="Top" Width="120">
<TextBox.InputBindings>
<KeyBinding Key="Enter" Command="{Binding LoginCommand}" />
</TextBox.InputBindings>
</TextBox>
<Label Content="Username" Height="28" HorizontalAlignment="Left" Margin="28,18,0,0" Name="label1" VerticalAlignment="Top" />
<Label Content="Password" Height="28" HorizontalAlignment="Left" Margin="29,47,0,0" Name="label2" VerticalAlignment="Top" />
<PasswordBox attach:PasswordBoxAssistant.BindPassword="True" attach:PasswordBoxAssistant.BoundPassword="{Binding Password, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Height="23" HorizontalAlignment="Left" Margin="100,50,0,0" Name="passwordBox1" VerticalAlignment="Top" Width="120" />
<Button Style="{DynamicResource RedSubmitButtonStyle}" IsDefault="{Binding ElementName=passwordBox1, Path=IsKeyboardFocused}" Command="{Binding LoginCommand}" Content="Login" Height="23" HorizontalAlignment="Left" Margin="145,86,0,0" Name="button1" VerticalAlignment="Top" Width="75" />
<Button Style="{DynamicResource RedSubmitButtonStyle}" Command="{Binding LazyLoginCommand}" Visibility="{Binding IsDebugMode, Converter={StaticResource visConv}}" Content="Quick Login" Height="23" HorizontalAlignment="Left" Margin="23,87,0,0" Name="button2" VerticalAlignment="Top" Width="89" />
</Grid>
</xctk:BusyIndicator>
</xctk:ChildWindow>
</Grid>