WPF TextBox won't fill in StackPanel

Question

I have a TextBox control within a StackPanel whose Orientation is set to Horizontal, but can't get the TextBox to fill the remaining StackPanel space.

XAML:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Height="180" Width="324">

    <StackPanel Background="Orange" Orientation="Horizontal" >
        <TextBlock Text="a label" Margin="5" VerticalAlignment="Center"/>
        <TextBox Height="25" HorizontalAlignment="Stretch" Width="Auto"/>
    </StackPanel>
</Window>

And this is what it looks like:

Why is that TextBox not filling the StackPanel?

I know I can have more control by using a Grid control, I'm just confused about the layout.

Answer 1

I've had the same problem with StackPanel, and the behavior is "by design". StackPanel is meant for "stacking" things even outside the visible region, so it won't allow you to fill remaining space in the stacking dimension.

You can use a DockPanel with LastChildFill set to true and dock all the non-filling controls to the Left to simulate the effect you want.

<DockPanel Background="Orange" LastChildFill="True">
    <TextBlock Text="a label" Margin="5" 
        DockPanel.Dock="Left" VerticalAlignment="Center"/>
    <TextBox Height="25" Width="Auto"/>
</DockPanel >