Why my WPF Rectangle control is not filling all the empty space of StackPanel?

Question

Learning basic concepts of WPF before moving to UWP. Following XAML in my WPF project is showing the windows as below.

I'm trying to display the Rectangle and Button on the right side of the StackPanel and need the Rectangle (not the Button) control to auto fill the StackPanel.

I tried the HorizontalAlignment="Stretch" with no Width attribute but without Width attribute the entire rectangle shrinks to 0 width. Don't want to hard code the width value (if possible) so that window of the app adjust itself depending on the device it's on (screen resolution). But if that scenario is still possible with hard coded width value as well please let me know that approach as well.

Window:

XAML:

Remark: I don't think ListBox is playing any role (related to this post). Only controls inside the ListItemsControl on above ListBox probably need proper adjustment. but I may be wrong.

<Window x:Class="WPFProject.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow"
        Height="376"
        Width="337">
    <Grid>
        <ItemsControl>
            <StackPanel Orientation="Horizontal" HorizontalAlignment="Stretch" Height="10">
                <Rectangle x:Name="myRectangle" Fill="#FFF4F4F5" HorizontalAlignment="Right" Height="9" Margin="0,0,0,0" Stroke="Black" VerticalAlignment="Top" Width="100"  RenderTransformOrigin="0.533,0.6"/>
                <Button Content="&#xE1FD;" HorizontalAlignment="Right" Height="10" VerticalAlignment="Top" FontSize="5" FontWeight="Bold"/>
            </StackPanel>
        </ItemsControl>
        <ListBox HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="0,11,0,81" ScrollViewer.HorizontalScrollBarVisibility="Disabled" x:Name="myList" SelectionChanged="myList_ContextMenuClosing">
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <WrapPanel IsItemsHost="True" Orientation="Horizontal"/>
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Rectangle Fill="{Binding FirstName}" ToolTip="{Binding FullName}" Width="20" Height="20" Stroke="#FF211E1E" OpacityMask="Black" StrokeThickness="1" />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <Button x:Name="btnTest" Content="Test" HorizontalAlignment="Left" Margin="250,298,0,0" VerticalAlignment="Top" Width="75" Click="BtnTest_Click"/>
    </Grid>
</Window>

If the ListBox is not playing a role, then it should not be in the code you posted. And for that matter, why are you putting your `StackPanel` inside the `ItemsControl`? — Peter Duniho, Jul 11 '19 at 00:28

score 3 · Accepted Answer · answered Jul 11 '19 at 05:36

Two things here:

When you use Stackpanel with horizontal orientation, horizontalalingment="stretch" can't be used. That is because all of the elements are being Stacked with their designed width.
You are specifying a fixed width of 100 for your rectangle. If you do that it will not stretch anymore even if you use stretch for alignment. Also the horizontalalingment="stretch" needs to be placed on the element you are expecting to stretch, not the Panel.

For things like this use DockPanelor a Grid instead. Read more about WPF panels here: https://wpf-tutorial.com/panels/introduction-to-wpf-panels/

Here is an example for Grid:

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="Auto"/>
    </Grid.ColumnDefinitions>
    <Rectangle x:Name="myRectangle" Fill="#FFF4F4F5" HorizontalAlignment="Stretch" Height="9" Margin="0,0,0,0" 
            Stroke="Black" VerticalAlignment="Top"  RenderTransformOrigin="0.533,0.6" Grid.Row="0"/>
    <Button Content="&#xE1FD;" HorizontalAlignment="Right" Height="10" VerticalAlignment="Top" FontSize="5" FontWeight="Bold" Grid.Column="1"/>
</Grid>

Notice the width="*" attribute means the cell will use all the remaining space. If you have multiple rows/columsn defined with * the space will be divided between them.

Thanks for explaining some important points related to the subject matter at hand. Reading some other posts (such as [this one](https://stackoverflow.com/a/36634/1232087) with more than 200 points I thought `horizontalalingment="stretch"` would do the trick, but the context there seems different because in my case I was trying `horizontalalingment="stretch"` with horizontal orientation that - according to your point 1 - we' can't do and - as you mentions in your point 2- I was using `horizontalalingment="stretch"` on the wrong element. — nam, Jul 11 '19 at 14:50

score 0 · Answer 2 · answered Jul 11 '19 at 06:45

Stack Panel acts like a stack of things placed one after another. It can be horizontal or vertical. Unlike Grid you cannot access particular place in a stack panel, every next element will be placed after one another in a sequence.For your requirement a StackPanel is not suitable unless you need to have horizontal scrolling. You should try a DockPanel or Grid instead like

           <Grid   Height="10">                
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition Width="auto"/>
                </Grid.ColumnDefinitions>
                <!--first column of grid-->
                <Rectangle Grid.Column="0" x:Name="myRectangle" Fill="#FFF4F4F5"  Height="9" Margin="0,0,0,0" Stroke="Black" VerticalAlignment="Top"   RenderTransformOrigin="0.533,0.6"/>
                <!--second column of grid-->
                <Button Grid.Column="1" Content="&#xE1FD;" HorizontalAlignment="Right" Height="10" VerticalAlignment="Top" FontSize="5" FontWeight="Bold"/>
            </Grid>

Why my WPF Rectangle control is not filling all the empty space of StackPanel?

2 Answers2