Question

I have the following XAML:

<TextBlock Text='{Binding ElementName=EditListBox, Path=SelectedItems.Count}' Margin='0,0,5,0'/> <TextBlock Text='items selected'>     <TextBlock.Style>         <Style TargetType='{x:Type TextBlock}'>             <Style.Triggers>                 <DataTrigger Binding='{Binding ElementName=EditListBox, Path=SelectedItems.Count}' Value='1'>                     <Setter Property='TextBlock.Text' Value='item selected'></Setter>                 </DataTrigger>             </Style.Triggers>         </Style>     </TextBlock.Style> </TextBlock> 

The first text block happily changes with SelectedItems.Count, showing 0,1,2, etc. The datatrigger on the second block never seems to fire to change the text.

Any thoughts?

Answer 1

The DataTrigger is firing but the Text field for your second TextBlock is hard-coded as ‘items selected’ so it won’t be able to change. To see it firing, you can remove Text=’items selected’.

Your problem is a good candidate for using a ValueConverter instead of DataTrigger. Here’s how to create and use the ValueConverter to get it to set the Text to what you want.

Create this ValueConverter:

public class CountToSelectedTextConverter : IValueConverter {     #region IValueConverter Members      public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)     {         if ((int)value == 1)             return 'item selected';         else             return 'items selected';     }      public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)     {         throw new NotImplementedException();     }      #endregion } 

Add the namespace reference to your the assembly the converter is located:

xmlns:local='clr-namespace:ValueConverterExample' 

Add the converter to your resources:

<Window.Resources>     <local:CountToSelectedTextConverter x:Key='CountToSelectedTextConverter'/> </Window.Resources> 

Change your second textblock to:

    <TextBlock Text='{Binding ElementName=EditListBox, Path=SelectedItems.Count, Converter={StaticResource CountToSelectedTextConverter}}'/>