NotifyDataErrorInfo

NotifyDataErrorInfo.cs

public class NotifyDataErrorInfo : INotifyPropertyChanged, INotifyDataErrorInfo
{
    private readonly Dictionary<string, List<string>> _errorsByPropertyName = new Dictionary<string, List<string>>();
    private readonly Func<IdentityUserVM, bool> PropertyUniquityValidationCallback;
    
    private string property;
    public string Property
    {
        get => base.UserName;
        set
        {
            property = value;
            OnPropertyChanged();
            ValidateUserName();
        }
    }

    private void ValidateProperty()
    {
        ClearErrors(nameof(Property));
        if (string.IsNullOrWhiteSpace(Property))
            AddError(nameof(Property), "ololo pysch pysch");
        if(!PropertyUniquityValidationCallback(this))
            AddError(nameof(Property), "upchck");
    }


    #region notify property changed
    /// <inheritdoc/>
    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged([CallerMemberName]string prop = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(prop));
    #endregion

    #region notify on errors
    private void OnErrorsChanged(string propertyName) => ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));

    /// <inheritdoc/>
    public bool HasErrors => _errorsByPropertyName.Any();

    /// <inheritdoc/>
    public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

    /// <inheritdoc/>
    public IEnumerable GetErrors(string propertyName)
    {
        if (string.IsNullOrWhiteSpace(propertyName))
            return _errorsByPropertyName.Values.SelectMany(x => x);
        return _errorsByPropertyName.ContainsKey(propertyName) ? _errorsByPropertyName[propertyName] : null;
    }

    private void AddError(string propertyName, string error)
    {
        if (!_errorsByPropertyName.ContainsKey(propertyName))
            _errorsByPropertyName[propertyName] = new List<string>();

        if (!_errorsByPropertyName[propertyName].Contains(error))
        {
            _errorsByPropertyName[propertyName].Add(error);
            OnErrorsChanged(propertyName);
        }
    }

    private void ClearErrors(string propertyName)
    {
        if (_errorsByPropertyName.ContainsKey(propertyName))
        {
            _errorsByPropertyName.Remove(propertyName);
            OnErrorsChanged(propertyName);
        }
    }
    #endregion

    public NotifyDataErrorInfo(Func<NotifyDataErrorInfo, bool> propertyUniquityValidationCallback)
    {
        PropertyUniquityValidationCallback = propertyUniquityValidationCallback ?? throw new ArgumentNullException(nameof(propertyUniquityValidationCallback));            
    }
}