WPF/MVVM: Why does my GUI not update?

I have a problem with WPF and MVVM. I created a Sudokufield consisting of 3 classes:

• SudokuFieldViewModel: The whole playing field (consists of 3*3 SudokuFieldBlockViewModels)
• SudokuBlockViewModel: One block of 3*3 SodokuBoxViewModels
• SudokuBoxViewModel: A box where a number between 1 and 9 can be entered

The SudokuBoxViewModel has a IsHighlighted-property of type bool.

I created a method Highlight in the SudokuFieldViewModel that calls a Highlight-method on every SudokuBlockViewModel which then sets IsHighlighted to true for all the SudokuBoxViewModels.

The property in BoxViewModel looks like this:

    private bool m_IsHighlighted = false;
    public bool IsHighlighted
    {
        get
        {
            return m_IsHighlighted;
        }

        set
        {
            if (m_IsHighlighted != value)
            {
                m_IsHighlighted = value;
                RaisePropertyChanged("IsHighlighted");
            }
        }
    }

The views are layed out in a way that FieldView has an ItemsControl with DataTemplates binding to the BlockViewModels in the FieldViewModel. The same concept applies to BoxViewModels in the BlockViewModel.

SudokuBlock:

<UserControl x:Class="SuSo.SudokuBlock"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
     <SuSo_Common:HighlightConverter x:Key="HighlightConverter"/>
        <DataTemplate x:Key="BlockBoxTemplate">
            <Grid>
                <local:SudokuBox DataContext="{Binding}" />
            </Grid>
        </DataTemplate>
    </UserControl.Resources>
    <Border BorderThickness="1" BorderBrush="Black">
        <ItemsControl ItemsSource="{Binding Elements, Mode=OneWay}" ItemTemplate="{DynamicResource BlockBoxTemplate}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid
                        Rows="{Binding Size, Mode=OneWay}" 
                        Columns="{Binding Size, Mode=OneWay}" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
        </ItemsControl>
    </Border>
</UserControl>

SudokuBox:

<UserControl x:Class="SuSo.SudokuBox"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
     <SuSo_Common:HighlightConverter x:Key="HighlightConverter"/>
        <DataTemplate x:Key="NumberTemplate" DataType="int">
            <Grid>
                <Viewbox Stretch="Fill" d:LayoutOverrides="Width, Height" >
                    <TextBlock x:Name="possibleNumber" Tex开发者_运维百科t="{Binding Mode=OneWay}" FontFamily="Hobo Std" TextAlignment="Center" Height="Auto" Margin="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="{Binding ActualHeight, ElementName=possibleNumber, Mode=OneWay}" />
                </Viewbox>
            </Grid>
        </DataTemplate>
    </UserControl.Resources>
    <UserControl.DataContext>
            <local:SudokuBoxViewModel Size="3" />
    </UserControl.DataContext>
    <Border BorderThickness="1" BorderBrush="Black" Background="{Binding IsHighlighted, Converter={StaticResource HighlightConverter}}">
        <ItemsControl ItemsSource="{Binding Elements, Mode=OneWay}" ItemTemplate="{DynamicResource NumberTemplate}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid
                        Rows="{Binding Size, Mode=OneWay}" 
                        Columns="{Binding Size, Mode=OneWay}" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
        </ItemsControl>
    </Border>
</UserControl>

The BoxView binds to IsHighlighted and uses a ValueConverter to convert the bool value to a SolidColorBrush that is used as background for the BoxView.

The problem however is that the GUI doesn't update when I call the Highlight function.

What could be the problem?

---

Oh my god!

The lines

<UserControl.DataContext>
        <local:SudokuBoxViewModel Size="3" />
</UserControl.DataContext>

were the problem (it becomes pretty obvious now..).

I removed this and now it works as it should :).