How to get Textblock with TextTrimming over an AdornedElementPlaceholder? - wpf

Question

I'm trying to get a ValidationRule to display text over an offending combobox, if the user has not specified a value yet. I can get it to display, but I can't seem to get the text to fit to the size of the combobox using TextTrimming="CharacterEllipsis". How can I get the TextBlock to fit the combobox, and also correct itself if the user resizes the window?
Here's my MainWindow.xaml:
<Window x:Class="PocAdornedElementPlaceholder.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:PocAdornedElementPlaceholder"
Title="MainWindow" Height="200" Width="150">
<Window.Resources>
<ControlTemplate x:Key="ValidationTemplate">
<Grid HorizontalAlignment="Center">
<AdornedElementPlaceholder/>
<TextBlock Foreground="Red"
TextTrimming="CharacterEllipsis"
Text="{Binding ErrorContent}"
IsHitTestVisible="False"
VerticalAlignment="Center"
Margin="5,0,0,0"/>
</Grid>
</ControlTemplate>
</Window.Resources>
<Grid>
<ComboBox Margin="10"
Validation.ErrorTemplate="{StaticResource ValidationTemplate}"
VerticalAlignment="Center"
ItemsSource="{Binding Options}">
<ComboBox.Text>
<Binding Path="SelectedValue">
<Binding.ValidationRules>
<local:MyValidationRule ValidatesOnTargetUpdated="True" />
</Binding.ValidationRules>
</Binding>
</ComboBox.Text>
</ComboBox>
</Grid>
</Window>
Here's my MainWindow.xaml.cs:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
Options = new List<string>() { "Value 1", "Value 2", "Value 3", "" };
this.DataContext = this;
}
public string SelectedValue { get; set; }
public List<string> Options { get; set; }
}
And here's my MyValidationRule.cs file:
public class MyValidationRule : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
if (string.IsNullOrEmpty((string)value))
return new ValidationResult(false, "Value cannot be empty!");
return new ValidationResult(true, null);
}
}
Any help would be much appreciated!
Thanks,
Tam

Answer 1

Try below, TextBlock should be the content of the adorner. I also had to change the margin of the textblock to count for the dropdown arrow button.
<ControlTemplate x:Key="ValidationTemplate">
<Grid HorizontalAlignment="Center">
<AdornedElementPlaceholder>
<TextBlock Foreground="Red" TextTrimming="CharacterEllipsis" Text="{Binding ErrorContent}" IsHitTestVisible="False" VerticalAlignment="Center" Margin="5,0,20,0" />
</AdornedElementPlaceholder>
</Grid>
</ControlTemplate>