Question

How can I constrain a vertical WPF StackPanel‘s width to the most narrow item it contains. The StackPanel‘s width must not be greater than the width of any other child element.

Answer 1

Unfortunately the IValueConverter approach will not always work; if the children are added to StackPanel statically, for example, the child collection will be empty at the time of binding (so I discovered). The simplest solution is to create a custom panel:

public class ConstrainedStackPanel : StackPanel {     public ConstrainedStackPanel()     {     }      protected override Size MeasureOverride(Size constraint)     {         foreach (var item in this.Children)         {             // FrameworkElement has the Width property we care about.             FrameworkElement element = item as FrameworkElement;             if (element != null)                 constraint.Width = Math.Min(element.Width, constraint.Width);         }          return base.MeasureOverride(constraint);     }      protected override Size ArrangeOverride(Size arrangeSize)     {         foreach (var item in this.Children)         {             // FrameworkElement has the Width property we care about.             FrameworkElement element = item as FrameworkElement;             if (element != null)                 arrangeSize.Width = Math.Min(element.Width, arrangeSize.Width);         }          return base.ArrangeOverride(arrangeSize);     } } 

You can use the panel as illustrated by the following XAML:

<StackPanel Margin='5'>     <TextBlock Text='StackPanel:' FontWeight='Bold' />     <StackPanel x:Name='panelA'>         <Button Width='100' Content='100' />         <Button Width='200' Content='200' />         <Button Width='300' Content='300' />         <Button Width='400' Content='400' />     </StackPanel>     <TextBlock Text='ConstrainedStackPanel:' FontWeight='Bold' Margin='0,10,0,0' />     <l:ConstrainedStackPanel x:Name='panelB'>         <Button Width='100' Content='100' />         <Button Width='200' Content='200' />         <Button Width='300' Content='300' />         <Button Width='400' Content='400' />     </l:ConstrainedStackPanel> </StackPanel> 

Which will render something like the following:

I hope this helps.