WPF validation error style in reuseable UserControl? - wpf

Question

I have made a reusable UserControl in my WPF application that has a Textbox (and in the real project other components) inside of it. I'm using Fluent Validation with INotifyDataErrorInfo to validate user input in TextBoxes. My problem is that when the model whose property is bound to the UserControl's TextBox has errors, the TextBox's style doesn't trigger according to the style that is set. It seems that my style's trigger for the UserControl's Textbox can't read the Validation.HasError value from the model correctly. So is there a way to get the style to trigger and get the error tooltip for the UserControl's Textbox?
This question has been asked by several other people over the years, and I have looked at every single one of them, but none of them really work for me. One thing I tried that does work is a general ValidationRule in the UserControl.xaml for the textbox binding, but that doesn't allow for model specific rules. I'm hoping that some WPF guru will finally take the challenge and solve this problem! :)
If you make a sample project from the code I provided, and set the Height property to less than 10, you see that the normal TextBox gets the triggered errorstyle with the tooltip, but the UserControl's TextBox gets the basic red border:
Sample app with the cursor over the first textbox.
Here is my simplified code:
The UserControl:
<UserControl x:Class="UserControlValidationTest.DataInputUserControl"
x:Name="parentControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="450" d:DesignWidth="800">
<UserControl.Resources>
<Style TargetType="TextBox" x:Key="TextBoxStyle">
<Style.Triggers>
<Trigger Property= "Validation.HasError" Value="true">
<Setter Property="Background" Value="Pink"/>
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
</Trigger>
</Style.Triggers>
</Style>
</UserControl.Resources>
<StackPanel Orientation="Horizontal" DataContext="{Binding ElementName=parentControl}">
<TextBox Name="ValueBox" Text="{Binding Value, UpdateSourceTrigger=PropertyChanged}" Width="60" Style="{StaticResource TextBoxStyle}"/>
</StackPanel>
public partial class DataInputUserControl : UserControl
{
public DataInputUserControl()
{
InitializeComponent();
Validation.SetValidationAdornerSite(this, ValueBox);
}
public double Value
{
get => (double)GetValue(ValueProperty);
set => SetValue(ValueProperty, value);
}
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(double), typeof(DataInputUserControl), new FrameworkPropertyMetadata(0d, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
}
MainWindow.xaml:
<Window x:Class="UserControlValidationTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:UserControlValidationTest"
mc:Ignorable="d"
Title="MainWindow" Height="100" Width="200">
<Window.DataContext>
<local:MainWindowViewModel/>
</Window.DataContext>
<Window.Resources>
<Style TargetType="TextBox">
<Style.Triggers>
<Trigger Property= "Validation.HasError" Value="true">
<Setter Property="Background" Value="Pink"/>
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
</Trigger>
</Style.Triggers>
</Style>
</Window.Resources>
<StackPanel>
<TextBox Text="{Binding User.Height, UpdateSourceTrigger=PropertyChanged}" Width="60" Margin="10"/>
<local:DataInputUserControl Value="{Binding User.Height}" HorizontalAlignment="Center"/>
</StackPanel>
View model:
public class MainWindowViewModel
{
public UserModel User { get; set; }
public MainWindowViewModel()
{
User = new UserModel();
}
}
User Model:
public class UserModel : ValidatableModel
{
public double Height { get => GetPropertyValue<double>(); set => SetPropertyValue(value); }
public UserModel()
{
ModelValidator = new UserValidator();
Height = 180;
}
}
User Validator:
public class UserValidator : AbstractValidator<UserModel>
{
public UserValidator()
{
RuleFor(x => x.Height)
.GreaterThan(10);
}
}
Validatable Model:
using FluentValidation;
using FluentValidation.Results;
using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
public abstract class ValidatableModel : INotifyDataErrorInfo, INotifyPropertyChanged
{
private readonly Dictionary<string, object> propertyBackingDictionary = new Dictionary<string, object>();
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string parameter = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(parameter));
}
protected T GetPropertyValue<T>([CallerMemberName] string propertyName = null)
{
if (propertyBackingDictionary.TryGetValue(propertyName, out object value))
{
return (T)value;
}
return default(T);
}
protected bool SetPropertyValue<T>(T newValue, [CallerMemberName] string propertyName = null)
{
if (EqualityComparer<T>.Default.Equals(newValue, GetPropertyValue<T>(propertyName)))
{
return false;
}
propertyBackingDictionary[propertyName] = newValue;
OnPropertyChanged(propertyName);
Validate();
return true;
}
private ConcurrentDictionary<string, List<string>> errors = new ConcurrentDictionary<string, List<string>>();
public IValidator ModelValidator { get; set; }
public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;
public void OnErrorsChanged(string propertyName)
{
ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));
}
public IEnumerable GetErrors([CallerMemberName] string propertyName = null)
{
errors.TryGetValue(propertyName, out List<string> errorsForName);
return errorsForName;
}
public bool HasErrors => errors.Count > 0;
public void Validate()
{
errors.Clear();
var validationResults = ModelValidator.Validate(this);
foreach (var item in validationResults.Errors)
{
errors.TryAdd(item.PropertyName, new List<string> { item.ErrorMessage });
OnErrorsChanged(item.PropertyName);
}
}
}
}