ComboBox HorizontalContentAlignment="Stretch" is not working

[shaosss]

Describe the bug When HorizontalContentAlignment="Stretch" is set it is rendered the same as with HorizontalContentAlignment="Center". Other values (Center, Left and Right) values works as expected.

To Reproduce Insert this control to the page:

        <ComboBox HorizontalAlignment="Stretch" Grid.Column="0" 
                  HorizontalContentAlignment="Stretch" SelectedIndex="0">
            <ComboBoxItem>
                <Grid RowDefinitions="100" ColumnDefinitions="100,*">
                    <Image Grid.Column="0" DockPanel.Dock="Left" Height="100" Width="100"></Image>
                    <StackPanel Grid.Column="1" Height="100">
                        <Label HorizontalAlignment="Stretch" Margin="4">Name</Label>
                        <ProgressBar HorizontalAlignment="Stretch" Margin="4"></ProgressBar>
                        <Label HorizontalAlignment="Stretch" Margin="4">Formats</Label>
                    </StackPanel>
                </Grid>
            </ComboBoxItem>
        </ComboBox>

Expected behavior A selected Item is shown stretched (same as items in dropdown).

Screenshots Here is the example:

Desktop (please complete the following information):

• OS: Windows
• Version 0.10.0

[maxkatz6]

It doesn't work with control items in combobox, because in this case Viewbox is used to display content. As a workaround Items with ItemTemplate should work.