Wpf – Setting TextBox.Width=”*” via Code

There are also some properties you can set to force a control to fill its available space when it would otherwise not do so. For example, you can say:

HorizontalContentAlignment="Stretch"

... to force the contents of a control to stretch horizontally. Or you can say:

HorizontalAlignment="Stretch"

... to force the control itself to stretch horizontally to fill its parent.

For Blend, a little known trick is to add these attributes to your usercontrol or window:

 xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
mc:Ignorable="d"
       d:DesignHeight="500" d:DesignWidth="600"

This will set the design height and width to 500 and 600 respectively. However this will only work for the blend designer. Not the Visual Studio Designer.

As far as the Visual Studio Designer your technique is all that works. Which is why I don't use the Visual Studio Designer. ;)