Windows App determine if TextBlock is trimmed - windows-8.1

Question

I have an GridItem that has a fixed Height/Width.
It contains a textblock that has the max line set.
How can I determine if this text is trimmed?
I want to add special functionality if it is trimmed.

Answer 1

Old Way - when TextWrapping is set to None
To know if a TextBlock is trimmed, we can subscribe to its SizeChanged event and compare its ActualWidth to the MaxWidth you specified. To get the right ActualWidth of the TextBlock, we will need to leave the TextTrimming to its default value (i.e. TextTrimming.None), and set it to trimmed once the width goes over.
New Way - when TextWrapping is set to Wrap
Now that I know because the TextWrapping is set to Wrap and assume the VirticalAlignment is not specified (default to Stretch), the Width will always stay the same. We only need to monitor the SizeChanged event when the actual height of the TextBlock exceeds the height of its parent.
Let's use a Behavior to encapsulate all the logic above. What needs to be mentioned here is that a static helper class with a bunch of attached properties or a new control that inherits from TextBlock can do exactly the same thing; but being a big Blend fan, I prefer to use Behaviors whenever possible.
The Behavior
public class TextBlockAutoTrimBehavior : DependencyObject, IBehavior
{
public bool IsTrimmed
{
get { return (bool)GetValue(IsTrimmedProperty); }
set { SetValue(IsTrimmedProperty, value); }
}
public static readonly DependencyProperty IsTrimmedProperty =
DependencyProperty.Register("IsTrimmed", typeof(bool), typeof(TextBlockAutoTrimBehavior), new PropertyMetadata(false));
public DependencyObject AssociatedObject { get; set; }
public void Attach(DependencyObject associatedObject)
{
this.AssociatedObject = associatedObject;
var textBlock = (TextBlock)this.AssociatedObject;
// subscribe to the SizeChanged event so we will know when the Width of the TextBlock goes over the MaxWidth
textBlock.SizeChanged += TextBlock_SizeChanged;
}
private void TextBlock_SizeChanged(object sender, SizeChangedEventArgs e)
{
// ignore the first time height change
if (e.PreviousSize.Height != 0)
{
var textBlock = (TextBlock)sender;
// notify the IsTrimmed dp so your viewmodel property will be notified via data binding
this.IsTrimmed = true;
// unsubscribe the event as we don't need it anymore
textBlock.SizeChanged -= TextBlock_SizeChanged;
// then we trim the TextBlock
textBlock.TextTrimming = TextTrimming.WordEllipsis;
}
}
public void Detach()
{
var textBlock = (TextBlock)this.AssociatedObject;
textBlock.SizeChanged += TextBlock_SizeChanged;
}
}
The XAML
<Grid HorizontalAlignment="Center" Height="73" VerticalAlignment="Center" Width="200" Background="#FFD2A6A6" Margin="628,329,538,366">
<TextBlock x:Name="MyTextBlock" TextWrapping="Wrap" Text="test" FontSize="29.333">
<Interactivity:Interaction.Behaviors>
<local:TextBlockAutoTrimBehavior IsTrimmed="{Binding IsTrimmedInVm}" />
</Interactivity:Interaction.Behaviors>
</TextBlock>
</Grid>
Note that the Behavior exposes a dependency property IsTrimmed, you can data bind it to a property in your viewmodel (i.e. IsTrimmedInVm in this case).
P.S. There's no FormattedText function in WinRT otherwise the implementation could be a little bit different.

Answer 2

We ended up making a static function
// Ensure block does not have MAXLINES or text trimming set prior to checking
public static bool IsTruncated(TextBlock block, int maxLines)
{
if (block == null)
{
throw new ArgumentNullException("block");
}
//the cut-off height is the height at which text will be cut off in the UI
var cutOffHeight = maxLines * block.LineHeight;
//determine whether the actual height of the TextBlock is greater than the cut-off height
return block.ActualHeight > cutOffHeight;
}
The trick is to make sure that Maxlines and text trimming is NOT set on the Textblock prior to running this function. After this function returns, that is when the Maxlines is set. In my case I just saved the returned Boolean in a containing object so I knew it was longer. Then I set maxlines and another button to see the extended content based on that Boolean.