INotifyDataErrorInfo implementation for several values, check that there are no errors in Dictionary (WPF MVVM)

Question

I have been trying to implement INotifyDataErrorInfo and everything seems to be working except SaveSettings() and especially bool HasErrors. Can somebody please tell me why and how to fix it?

I mean that SaveSettings is always triggered, even if there are errors in TextBoxes. It should be triggered only if there are no errors.

ViewModel.cs:

using System;
using System.Collections;
using System.ComponentModel;
using System.Windows;
using System.Windows.Input;

namespace SimpleValidator.ViewModels
{
    public class ViewModel : BaseViewModel, INotifyDataErrorInfo
    {
        private readonly PropertyErrors errors;

        public ICommand SaveCommand => new RelayCommand(param => this.SaveSettings());

        public ViewModel()
        {
            this.errors = new PropertyErrors(this, this.OnErrorsChanged);

            this.TimeLimit = "12:23";

            this.TimeRecordInterval = "11";
        }

        private void SaveSettings()
        {
            if (!HasErrors)
                MessageBox.Show("Save");
        }

        public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

        private string _timeLimit;
        public string TimeLimit
        {
            get { return this._timeLimit; }
            set
            {
                if (value == this._timeLimit)
                {
                    return;
                }

                this._timeLimit = value;
                this.errors.Clear(nameof(this.TimeLimit));
                OnPropertyChanged();
            }
        }

        private string _timeRecordInterval;
        public string TimeRecordInterval
        {
            get { return this._timeRecordInterval; }
            set
            {
                if (value == this._timeRecordInterval)
                {
                    return;
                }

                this._timeRecordInterval = value;
                this.errors.Clear(nameof(this.TimeRecordInterval));
                OnPropertyChanged();
            }
        }

        public bool HasErrors => this.errors.HasErrors;

        public IEnumerable GetErrors(string propertyName) => this.errors.GetErrors(propertyName);

        protected virtual void OnErrorsChanged(DataErrorsChangedEventArgs e)
        {
            this.ErrorsChanged?.Invoke(this, e);
        }
    }
}

Answer 1

Hi,
in your code you validate in 2 levels: UI and data object (in your case in ViewModel). Validation in UI level your code don't inform ViewModel. If you want inform ViewModel you can:

Set Validation.Error and NotifyOnValidationError="True"

<Label>Interval</Label>
<TextBox x:Name="TimeRecordInterval" Validation.Error="Validation_Error"
           Grid.Row="0"
           Grid.Column="1">
  <TextBox.Text>
    <Binding Path="TimeRecordInterval" NotifyOnValidationError="True"
                   UpdateSourceTrigger="PropertyChanged">
      <Binding.ValidationRules>
        <viewmodels:NumberValidationRule numberValidation="number" />
      </Binding.ValidationRules>
    </Binding>
      </TextBox.Text>
...

Include Event method:

using SimpleValidator.ViewModels;
using System.Windows;
using System.Windows.Controls;

namespace SimpleValidator
{
  /// <summary>
  /// Interaction logic for MainWindow.xaml
  /// </summary>
  public partial class MainWindow : Window
  {
    private ViewModel ViewModel { get; set; }

    public MainWindow()
    {
      ViewModel = new ViewModel();
      DataContext = ViewModel;
      InitializeComponent();
    }

    private void Validation_Error(object sender, System.Windows.Controls.ValidationErrorEventArgs e)
    {
      string name = ((TextBox)sender)?.Name;
      ViewModel.SetTimeRecordInterval(name, e);
    }
  }
}

and in ViewModel:

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace SimpleValidator.ViewModels
{
  public class ViewModel : BaseViewModel, INotifyDataErrorInfo
  {
    private readonly PropertyErrors errors;

    public ICommand SaveCommand => new RelayCommand(param => this.SaveSettings(), 
      (obj) => !this.HasErrors && this.UiErrorMessages.Count==0);

    private readonly Dictionary<string, string> UiErrorMessages = new Dictionary<string, string>();

    public void SetTimeRecordInterval(string ctrlName, ValidationErrorEventArgs e)
    {
      if (e.Action == ValidationErrorEventAction.Added) this.UiErrorMessages[ctrlName] = e.Error.ErrorContent.ToString();
      if (e.Action == ValidationErrorEventAction.Removed) this.UiErrorMessages.Remove(ctrlName);
      OnPropertyChanged(nameof(SaveCommand));
    }

    private void SaveSettings()
    {
      if (!HasErrors && UiErrorMessages.Count == 0)
        MessageBox.Show("Save");
    }