Windows Phone 8.1 Toggling the visibility of a TextBlock in a DataTemplate - xaml

Question

I'm building a Windows Phone 8.1 Hub Application. One of the hub section contains a ListView that displays a list of articles. I'd like to add a Textblock to this hubsection which displays a message when the articles failed to download. The XAML Code is below:
<HubSection
x:Uid="ArticlesSection"
Header="ARTICLES"
DataContext="{Binding Articles}"
HeaderTemplate="{ThemeResource HubSectionHeaderTemplate}">
<DataTemplate>
<Grid>
<ListView
AutomationProperties.AutomationId="ItemListViewSection3"
AutomationProperties.Name="Items In Group"
SelectionMode="None"
IsItemClickEnabled="True"
ItemsSource="{Binding}"
ItemTemplate="{StaticResource BannerBackgroundArticleTemplate}"
ItemClick="ItemView_ItemClick"
ContinuumNavigationTransitionInfo.ExitElementContainer="True">
</ListView>
<TextBlock
x:Name="NoArticlesTextBlock"
HorizontalAlignment="Center"
VerticalAlignment="center"
Style="{StaticResource HeaderTextBlockStyle}"
TextWrapping="WrapWholeWords"
TextAlignment="Center"/>
</Grid>
</DataTemplate>
</HubSection>
The problem I'm having is that I can't access the TextBlock from the C# code. Is there an easier way to do this?

Answer 1

The problem I'm having is that I can't access the TextBlock from the C# code.
Yes, since the TextBlock is defined inside a DataTemplate, the TextBlock won't be available until the DataTemplate has been applied. Thus, the x:Name attribute won't automatically generate a variable reference in the InitializeComponent method in your *.g.i.cs file. (Read up on XAML Namescopes for more information).
If you want to access it from your code-behind, there are two ways:
The first way is the simplest: you can get a reference to the TextBlock in the sender argument of the Loaded event handler for that TextBlock.
<TextBlock Loaded="NoArticlesTextBlock_Loaded" />
Then in your code-behind:
private TextBlock NoArticlesTextBlock;
private void NoArticlesTextBlock_Loaded(object sender, RoutedEventArgs e)
{
NoArticlesTextBlock = (TextBlock)sender;
}
The second way is to traverse the visual tree manually to locate the element with the required name. This is more suitable for dynamic layouts, or when you have a lot of controls you want to reference that doing the previous way would be too messy. You can achieve it like this:
<Page Loaded="Page_Loaded" ... />
Then in your code-behind:
static DependencyObject FindChildByName(DependencyObject from, string name)
{
int count = VisualTreeHelper.GetChildrenCount(from);
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(from, i);
if (child is FrameworkElement && ((FrameworkElement)child).Name == name)
return child;
var result = FindChildByName(child, name);
if (result != null)
return result;
}
return null;
}
private TextBlock NoArticlesTextBlock;
private void Page_Loaded(object sender, RoutedEventArgs e)
{
// Note: No need to start searching from the root (this), we can just start
// from the relevant HubSection or whatever. Make sure your TextBlock has
// x:Name="NoArticlesTextBlock" attribute in the XAML.
NoArticlesTextBlock = (TextBlock)FindChildByName(this, "NoArticlesTextBlock");
}
Jerry Nixon has a good page on his blog about this.