Customize WPF databinding: How to add custom logic?

Question

Hi,

i have a question regarding some complex data-binding.
I want to be able to update a grid (which has the property "IsItemsHost" set to true)
dynamically whenever a data-binding occurs.
Actually i am using a CustomControl which is an ItemsControl and this
has the Grid in its ControlTemplate.

To be more specific, i bind the grid to some items and i want to change the number of grid rows depending on these items, add something like a header (one row containing some text), and set the items' Grid.Row and Grid.Column using some custom logic.

What is the easiest way to apply such behaviour whenever the bound data is updated?

Do i have to use a viewmodel that also contains the header data?

Thanks in advance.

Code of the CustomControl Generic.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TimeTableControl">
<Style TargetType="{x:Type local:TimeTableControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:TimeTableControl}">
                <Border Width="Auto" Height="Auto" BorderBrush="#FF4B5A9B" BorderThickness="4" CornerRadius="4" Margin="2" Padding="0" Background="White">
                    <Grid Width="Auto">
                        <Grid.RowDefinitions>
                            <RowDefinition Height="0.1*"/>
                            <RowDefinition Height="*"/>
                        </Grid.RowDefinitions>
                        <Viewbox>
                            <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=DayCaption}"/>
                        </Viewbox>
                        <Border Grid.Row="1" BorderThickness="0,2,0,0" BorderBrush="#FF4B5A9B">
                            <Grid Name="ContentGrid" IsItemsHost="True">
                            </Grid>
                        </Border>
                    </Grid>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
</ResourceDictionary>

Answer 1

Grid is used for layout. If you have a changing number of items in some collection, what you really want is ItemsControl, or more specific ListBox (if you want item selection, etc).

If you still want Grid-like behavior of individual rows, you may want to define a Grid in ItemsControl.ItemTemplate and play with Grid.IsSharedSizeScope at ItemsControl level. Alternatively, you may just use ListView instead to get the grid look and item selection in a package.

Answer 2

Update: I got it working by creating a custom panel that uses MeasureOverride and ArrangeOverride to update itself. This lets me adjust the panel to the children and I don't even need to use a grid. This also makes the control lookless.