How to get accordion region to expand (vertically) to dynamic content?

Question

I have a main datagrid, then an accordion control below it. In one of the accordion items I have another datagrid that binds to the selected item of the first datagrid. Simple xaml is:

<sdk:DataGrid Name="dgMain" ItemsSource="{Binding SomeSource}" />
<toolkit:Accordion>
    <toolkit:AccordionItem Header="Details">
        <sdk:DataGrid ItemsSource="{Binding ElementName=dgMain, Path=SelectedItem.Children}"/>
    </toolkit:AccordionItem>
</toolkit:Accordion>

I have VerticalAlignment property of the second grid set to "Stretch" so it stretches as different collection sizes are bound to it, but the problem is it only stretches within the AccordionItem size so if I select a new item in the first grid that has more "Children" then I have to scroll the second grid because the AccordionItem didn't change.

AccordionItem region will only change when i condense and expand it again. Setting VerticalContentAlignment to "Stretch" for the accordion item does not work. I guess because it only triggers this when first expanded.

Does anyone know what else I could try or if I'm missing something. I'd prefer to stick with xaml solution so I can stay MVVM-friendly, but glad to hear everything.

Answer 1

The reason that the AccordionItem doesn't resize properly is because there is a bug in one of its control Parts - ExpandableContentControl. The issue is described here.

I think you can either fix its source code or, more easily, replace this control from its default style with a normal ContentControl. I have included a style here with a normal ContentControl and tested it in the code that @JohnNicholas provided, and it works.

    <Style TargetType="toolkit:AccordionItem">
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="BorderBrush" Value="#FFECECEC"/>
        <Setter Property="Background" Value="White"/>
        <Setter Property="Margin" Value="0"/>
        <Setter Property="Padding" Value="0"/>
        <Setter Property="HorizontalAlignment" Value="Stretch"/>
        <Setter Property="VerticalAlignment" Value="Stretch"/>
        <Setter Property="HorizontalContentAlignment" Value="Left"/>
        <Setter Property="VerticalContentAlignment" Value="Top"/>
        <Setter Property="IsTabStop" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="toolkit:AccordionItem">
                    <Grid Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalAlignment}" VerticalAlignment="{TemplateBinding VerticalAlignment}">
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="CommonStates">
                                <VisualStateGroup.Transitions>
                                    <VisualTransition GeneratedDuration="0"/>
                                </VisualStateGroup.Transitions>
                                <VisualState x:Name="Normal"/>
                                <VisualState x:Name="Pressed"/>
                                <VisualState x:Name="MouseOver"/>
                                <VisualState x:Name="Disabled"/>
                            </VisualStateGroup>
                            <VisualStateGroup x:Name="FocusStates">
                                <VisualState x:Name="Focused"/>
                                <VisualState x:Name="Unfocused"/>
                            </VisualStateGroup>
                            <VisualStateGroup x:Name="ExpansionStates">
                                <VisualStateGroup.Transitions>
                                    <VisualTransition GeneratedDuration="0"/>
                                </VisualStateGroup.Transitions>
                                <VisualState x:Name="Collapsed">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0">
                                                <DiscreteObjectKeyFrame.Value>
                                                    <Visibility>Collapsed</Visibility>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="Expanded">
                                </VisualState>
                            </VisualStateGroup>
                            <VisualStateGroup x:Name="LockedStates">
                                <VisualStateGroup.Transitions>
                                    <VisualTransition GeneratedDuration="0"/>
                                </VisualStateGroup.Transitions>
                                <VisualState x:Name="Locked">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="IsEnabled" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="False"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="Unlocked">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="IsEnabled" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="True"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                            </VisualStateGroup>
                            <VisualStateGroup x:Name="ExpandDirectionStates">
                                <VisualStateGroup.Transitions>
                                    <VisualTransition GeneratedDuration="0"/>
                                </VisualStateGroup.Transitions>
                                <VisualState x:Name="ExpandDown">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Height" Storyboard.TargetName="rd1">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Width" Storyboard.TargetName="cd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="ExpandUp">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Row)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Row)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="0"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Height" Storyboard.TargetName="rd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Width" Storyboard.TargetName="cd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="ExpandLeft">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.ColumnSpan)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.ColumnSpan)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.RowSpan)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.RowSpan)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Column)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Row)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="0"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Height" Storyboard.TargetName="rd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Width" Storyboard.TargetName="cd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="ExpandRight">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.ColumnSpan)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.ColumnSpan)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.RowSpan)" Storyboard.TargetName="ExpanderButton">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.RowSpan)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="2"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Row)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="0"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Grid.Column)" Storyboard.TargetName="ExpandSite">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="1"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Height" Storyboard.TargetName="rd0">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Width" Storyboard.TargetName="cd1">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="*"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                        <Border x:Name="Background" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="1,1,1,1" Padding="{TemplateBinding Padding}">
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition x:Name="cd0" Width="Auto"/>
                                    <ColumnDefinition x:Name="cd1" Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <Grid.RowDefinitions>
                                    <RowDefinition x:Name="rd0" Height="Auto"/>
                                    <RowDefinition x:Name="rd1" Height="Auto"/>
                                </Grid.RowDefinitions>
                                <toolkit:AccordionButton x:Name="ExpanderButton" Background="{TemplateBinding Background}" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" Foreground="{TemplateBinding Foreground}" FontWeight="{TemplateBinding FontWeight}" FontStyle="{TemplateBinding FontStyle}" FontStretch="{TemplateBinding FontStretch}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalAlignment="{TemplateBinding HorizontalAlignment}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsTabStop="True" IsChecked="{TemplateBinding IsSelected}" Margin="0,0,0,0" Padding="0,0,0,0" Grid.Row="0" Style="{TemplateBinding AccordionButtonStyle}" VerticalAlignment="{TemplateBinding VerticalAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                                <ContentControl x:Name="ExpandSite" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Foreground="{TemplateBinding Foreground}" FontWeight="{TemplateBinding FontWeight}" FontStyle="{TemplateBinding FontStyle}" FontStretch="{TemplateBinding FontStretch}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalAlignment="{TemplateBinding HorizontalAlignment}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsTabStop="False" Margin="0,0,0,0" Grid.Row="1" Style="{TemplateBinding ExpandableContentControlStyle}" VerticalAlignment="{TemplateBinding VerticalAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                            </Grid>
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

PS. If you want to animate the expanding/collapsing you can just define your own animation in the AccordionItem's Collapsed and Expanded visual states.

It is really a late reply and hope it can be of any help. :)