Expander content is not focusable anymore

[chrizzz86]

Bug explanation

Due to setting Focusable="False" for ContentPresenter inside Grid "ContentPanel" it's not possible anymore to set focus on content controls

Version

4.6.0.0 prerelease

[ElieTaillard]

Indeed, it's problematic...

[greuelpirat]

I just tried the following

<Expander HorizontalAlignment="Stretch" Header="Expander Example 1a">
  <Button Content="Hello"></Button>
</Expander>

When I set Focusable=True this adds a tab stop to the content presenter:

1. ToggleButton (in Header)
2. ContentPresenter 🆕
3. Button "Hello"

(Unfortunately KeyboardNavigation.IsTabStop="False" does not work here for me)

Why do you need to focus the ContentPresenter? The button/content can still be focused.

[chrizzz86]

In my case I had a TextBox inside the Expander control. The focus was set automatically by DataTrigger when control expands. This was working properly in previous versions.

From version 4.6 there is a new setting Focusable="False" for the ContentPresenter Name="PART_Content" inside the ControlTemplate. I guess based on this change it is not working anymore.

[Keboo]

@chrizzz86 can you provide additional feedback on your setup. I wrote a UI test to try and reproduce the problem but I am unable to.

[chrizzz86]

Hi, yes, for sure...

<Expander ExpandDirection="Left"
                  DataContext="{Binding SearchViewModel}"
                  IsExpanded="{Binding IsExpanded, Mode=TwoWay}"
                  Style="{StaticResource MaterialDesignExpander}"
                  VerticalAlignment="Stretch"
                  HorizontalAlignment="Right">

            <Expander.Header>
                <TextBlock
                    Text="{x:Static loc:Controls.Search}"
                    RenderTransformOrigin=".5,.5">
                    <TextBlock.LayoutTransform>
                        <RotateTransform Angle="90" />
                    </TextBlock.LayoutTransform>
                </TextBlock>
            </Expander.Header>

            <GroupBox Margin="5"
                      Style="{StaticResource MaterialDesignCardGroupBox}">

                <GroupBox.Header>
                    <StackPanel Orientation="Horizontal">
                        <ContentPresenter Content="{StaticResource EventSearchWhite}" />
                        <TextBlock Text="{x:Static loc:Controls.SearchTooltip}"
                               Margin="3,0,0,0"
                               Foreground="White" />
                    </StackPanel>
                </GroupBox.Header>

                <DockPanel>

                    <TextBox DockPanel.Dock="Top"
                             GotFocus="TextBoxGotFocus"
                             Margin="5"
                             materialDesign:TextFieldAssist.HasClearButton="True"
                             materialDesign:HintAssist.Hint="{x:Static loc:Controls.FilterHint}"
                             VerticalAlignment="Center"
                             Text="{Binding Filter, UpdateSourceTrigger=PropertyChanged, Delay=200}">

                        <TextBox.InputBindings>
                            <KeyBinding Command="{Binding SelectCurrentItemAndCloseCommand}"
                                        Key="Return" />
                        </TextBox.InputBindings>

                        <TextBox.Style>
                            <Style TargetType="TextBox"
                                BasedOn="{StaticResource MaterialDesignOutlinedTextBox }">
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding IsExpanded}" Value="True">
                                        <Setter Property="FocusManager.FocusedElement" Value="{Binding RelativeSource={RelativeSource Self}}" />
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </TextBox.Style>

                    </TextBox>
                    
                    ...AND SOMETHING MORE...

                </DockPanel>

            </GroupBox>

        </Expander>

[greuelpirat]

Great, I reproduced your issue (needed some changes for DataContext etc...)

But even if I set Focusable="True" on the ContentPresenter PART_Content the focus when expanding does not work:

To be honest: I expected this, but I can not explain why this worked before. I will try make some additional tests. But I would recommend to keep Focusable=False due to the keyboard navigation behaviour.

[greuelpirat]

the focus works when changes from 0c8779003b9a497efd3b73a7b013742e42f015b3 are reverted:

The focus does not work anymore because the Expander-content is collapsed when FocusManager is called. I think #2579 is still a good change.

To make it work again, the focus must be delayed. The fasted way I found is to use an event handler to queue the focus with priority Loaded:

<Expander Expanded="OnExpanded" ...>
  <TextBox x:Name="TextBoxToFocus" ...>
</Expander>

private void OnExpanded(object sender, RoutedEventArgs e)
{
  Dispatcher.InvokeAsync(TextBoxToFocus.Focus, DispatcherPriority.Loaded);
}

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