Just give the TextBlock
a MaxWidth
which is the ActualWidth
of either the GroupBox
or in your case even the layoutGrid
(as your GroupBox
has the same width). This would force the TextBlock
to have to wrap when it's Width
exceeds that dimension and thereby giving you your requirement.
So something like:
<GroupBox x:Name="grpBox"
Grid.Row="2"
Grid.ColumnSpan="3">
<TextBlock MaxWidth="{Binding ElementName=grpBox,
Path=ActualWidth}"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Text="{Binding ...}"
TextWrapping="Wrap" />
</GroupBox>
or
<TextBlock MaxWidth="{Binding ElementName=layoutGrid,
Path=ActualWidth}"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Text="{Binding ...}"
TextWrapping="Wrap" />