WPF BindingGroup Validation

Question

I am using a StackPanel to host several TextBoxes that have validation rules attached.
I also have a StackPanel.BindingGroup validation as follows:

I have a BindingGroup validation rule called: ValidateAll from which I would like to display the error message in a TextBlock on my StatusBar.
I only want to display the BindingGroup:ValidateAll message as the TextBox validation messages are displayed below the TextBoxes.
I know I can do this in code by handling the ItemError event, where I can get the rule associated with an error message through the ValidationError.RuleInError property.
I would like to be able to accomplish this in xaml, possibly by setting up a Style/Trigger/Setter combination to my StatusBar TextBlock.
Any help would be much appreciated.

Accepted Answer

Hi, if you want to see default error information you can include your own conversion and use IDataError in dataobject like in following demo:

XAML:

-----------------------------------

using System;  
using System.Collections.Generic;  
using System.ComponentModel;  
using System.Globalization;  
using System.Runtime.CompilerServices;  
using System.Windows;  
using System.Windows.Controls;  
using System.Windows.Data;  
using System.Windows.Input;  
using System.Windows.Interactivity;  
  
namespace WpfApp44  
{  
  public class ViewModel  
  {  
    public Data View { get; set; } = new Data() { Name = "xxx" };  
    public ICommand Cmd { get => new RelayCommand((state) => { ValidateAllFields?.CommitEdit(); }, null); }  
    public BindingGroup ValidateAllFields { get; set; }  
  }  
  
  public class Data : IDataErrorInfo, INotifyPropertyChanged  
  {  
    private string _name = string.Empty;  
    public string Name  
    {  
      get => this._name;  
      set { this._name = value; errorMessages[nameof(Name)] = this[nameof(Name)]; OnPropertyChanged(); }  
    }  
  
    private int _age = 0;  
    private string _ageString = null;  
    public object Age  
    {  
      get => (this._ageString == null) ? this._age.ToString() : this._ageString;  
      set  
      {  
        if (value == null) this._ageString = "?";  
        else  
        {  
          this._ageString = value.ToString();  
          int.TryParse(value.ToString(), out this._age);  
          errorMessages[nameof(Age)] = this[nameof(Age)];  
          OnPropertyChanged();  
        }  
      }  
    }  
  
    private Dictionary errorMessages = new Dictionary();  
  
    public string Error  
    {  
      get  
      {  
        String result = String.Empty;  
        foreach (var item in errorMessages)  
          if (!string.IsNullOrEmpty(item.Value)) result += (string.IsNullOrEmpty(result)) ? item.Value : Environment.NewLine + item.Value;  
        return result;  
      }  
    }  
    public string this[string columnName]  
    {  
      get  
      {  
        string result = string.Empty;  
        switch (columnName)  
        {  
          case "Name": if (string.IsNullOrEmpty(Name)) result = "Name may not be null or empty"; break;  
          case "Age":  
            if (string.IsNullOrEmpty(this._ageString)) result = "Age may not be null or empty";  
            else if (this._age < 18 || this._age > 65) result = "Age must be beetween 18 an 65"; break;  
        };  
        return result;  
      }  
    }  
  
    public event PropertyChangedEventHandler PropertyChanged;  
    protected void OnPropertyChanged([CallerMemberName] string propertyName = "") =>  
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));  
  }  
  
  public class ValidateAll : ValidationRule  
  {  
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)  
    {  
      BindingGroup bindingGroup = (BindingGroup)value;  
      ViewModel vm = (ViewModel)bindingGroup.Items[0];  
      if (!string.IsNullOrEmpty(vm.View.Error)) return new ValidationResult(false, vm.View.Error);  
      return ValidationResult.ValidResult;  
    }  
  }  
  
  public class StackPanelBehavior : Behavior  
  {  
    protected override void OnAttached()  
    {  
      var vm = AssociatedObject.DataContext as ViewModel;  
      var bg = AssociatedObject.BindingGroup;  
      if (vm == null || bg == null) return;  
      vm.ValidateAllFields = bg;  
    }  
  }  
  
  public class RelayCommand : ICommand  
  {  
    private readonly Predicate

Answer

You can use Style/Trigger/Setter to implement the validation in the xaml and create the error message in the model class:

Model class:

 public class Person : IDataErrorInfo, INotifyPropertyChanged
    {
        private int age;

        public int Age
        {
            get { return age; }
            set {
                age = value;
                RaisePropertyChanged("Age");
            }
        }

        private string name;

        public string Name
        {
            get { return name; }
            set {
                name = value;
                RaisePropertyChanged("Name");
            }
        }

        #region IDataErrorInfo Members

        public string Error
        {
            get { return null; }
        }

        public string this[string columnName]
        {
            get
            {
                string result = string.Empty;
                switch (columnName)
                {
                    case "Name": if (string.IsNullOrEmpty(Name)) result = "Name is required!"; break;
                    case "Age": if ((Age < 1) || (Age > 100)) result = "Age must be between 1 and 100"; break;
                };
                return result;
            }
        }

        #endregion

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        #endregion
    }

Then set the trigger for the TextBox in xaml:

Add DataContext = new Person(); in this xaml.cs

Answer

Hi, try following MVVM demo. Button executes BindingGroup.CommitEdit. Error information will be displayed in DataTemplate in ContentPresenter in StatusBar.

XAML:

Code:

using System;
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Interactivity;

namespace WpfApp42
{
  public class ViewModel
  {
    public string Name { get; set; } =string.Empty;

    public ICommand Cmd { get => new RelayCommand((state) => { ValidateAllFields?.CommitEdit(); }, null); }

    public BindingGroup ValidateAllFields { get; set; }
  }

  public class ValidateAll : ValidationRule
  {
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
      BindingGroup bindingGroup = (BindingGroup)value;
      ViewModel vm = (ViewModel)bindingGroup.Items[0];
      if (string.IsNullOrEmpty(vm.Name)) return new ValidationResult(false, "Name may not be null or empty");
      return ValidationResult.ValidResult;
    }
  }

  public class StackPanelBehavior : Behavior
  {
    protected override void OnAttached()
    {
      var vm = AssociatedObject.DataContext as ViewModel;
      var bg = AssociatedObject.BindingGroup;
      if (vm == null || bg == null) return;
      vm.ValidateAllFields = bg;
    }
  }

  public class RelayCommand : ICommand
  {
    private readonly Predicate

Answer

Hi: Have corrected your code as requested and added:

using Microsoft.TeamFoundation.MVVM;
using ValidationRule = System.Windows.Controls.ValidationRule;

I found the Microsoft.TeamFoundation.Controls.dll in my implementation of VisualStudio2019 on my C: drive.
I thought it should be available through a NuGetPackage: the Microsoft.TeamFoundationServer.ExtendedClient, which I installed in my project but could not find it in the list of references or in the project directory.

I have added a property to your view model:

 public int Age { get; set; } = 0;

and the following TextBox to the MainWindow under the Name TextBox:

The purpose of adding the TextBox is I wanted to see if the default error handling message, (non integer value or Null) would be displayed in the StatusBar when selecting the Button, which it was. I only want to see the ValidateAll message on the StatusBar, the TestBox validations will be displayed in the adornment layer of the TextBox.

Answer

Here is my solution:

XAML:

Window x:Class="WpfGroupValidationDemo4.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:WpfGroupValidationDemo4"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

Code:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Globalization;
using System.Windows.Input;


namespace WpfGroupValidationDemo4
{
    /// 
    /// Interaction logic for MainWindow.xaml
    /// 
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = new ViewModel();
        }

        // This event occurs when a ValidationRule in the BindingGroup or in a Binding fails.
        //private void ItemError(object sender, ValidationErrorEventArgs e)
        //{

        //    if ((e.Action == ValidationErrorEventAction.Added) &&
        //        (e.Error.RuleInError.ToString() == "WpfGroupValidationDemo4.ValidateAll"))
        //    {
        //        StatusTextBlock.Text = e.Error.ErrorContent.ToString();
        //    }
        //    else
        //        StatusTextBlock.Text = String.Empty;
        //}

        private void ButtonClick(object sender, RoutedEventArgs e)
        {
            //this.TextBoxStack.BindingGroup.UpdateSources();

            if (!this.TextBoxStack.BindingGroup.UpdateSources())
                StatusTextBlock.Text = (string)this.TextBoxStack.BindingGroup.ValidationErrors[0].ErrorContent;
            else
                StatusTextBlock.Text = "Calculation Successful";
        }
    }

    public class ViewModel : INotifyPropertyChanged
    {

        public event PropertyChangedEventHandler PropertyChanged;   // Property changed event, raised when any of the Lease options are changed.

        public ViewModel()
        {
            this.name = "Allan";
            this.age = 30;
        }

        #region Properties

        private string name;
        public string Name
        {
            get { return this.name; }
            set
            {
                if (value != name)
                {
                    this.name = value;
                    this.OnPropertyChanged(nameof(Name));
                }
            }
        }
        private int age;
        public int Age
        {
            get { return this.age; }
            set
            {
                if (value != this.age)
                {
                    this.age = value;
                    this.OnPropertyChanged(nameof(Age));
                }
            }
        }

        #endregion Properties

        private void OnPropertyChanged([CallerMemberName] String propertyName = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    #region Validation Rules
    public class ValidateAgeRule : ValidationRule
    {
        public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
        {
            if (!int.TryParse(value.ToString(), out int i))
                return new ValidationResult(false, "Please enter a valid integer value.");

            if (i < 30 || i > 70)
                return new ValidationResult(false, "Age must be between 30 and 70");

            return new ValidationResult(true, null);

        }
    }

    public class ValidateNameRule : ValidationRule
    {
        public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
        {
            string name = (string)value;
            if (name != "Allan" && name != "Jim")
                return new ValidationResult(false, "Please enter the names: Allan or Jim");

            return new ValidationResult(true, null);
        }
    }


    public class ValidateAll : ValidationRule
    {

        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            if (value == null)
                return ValidationResult.ValidResult;

            BindingGroup bg = value as BindingGroup;

            ViewModel viewModel = bg.Items[0] as ViewModel;

            // Get the proposed values for age and name 
            bool ageResult = bg.TryGetValue(viewModel, "Age", out object ageValue);
            bool nameResult = bg.TryGetValue(viewModel, "Name", out object nameValue);

            if (!ageResult || !nameResult)
                return new ValidationResult(false, "Properties not found");

            int age = (int)ageValue;
            string name = (string)nameValue;

            if ((age == 30) && (name == "Jim"))
                return new ValidationResult(false, "Jim cannot be Thirty!");

            return ValidationResult.ValidResult;
        }
    }

    #endregion Validation Rules

    [ValueConversion(typeof(ValidationRule), typeof(Boolean))]
    public class ValidationRuleConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            Boolean returnValue = false;
            ValidationRule rule = (ValidationRule)value;
            String name = rule.ToString();

            if (name == "WpfGroupValidationDemo4.ValidateAll")
                returnValue = true;

            return returnValue;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
        }
    }

}

WPF BindingGroup Validation

5 additional answers