FeedCenter/Application/Feeds/DataErrorDictionary.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;

namespace FeedCenter;

internal class DataErrorDictionary : Dictionary<string, List<string>>
{
    public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

    private void OnErrorsChanged(string propertyName)
    {
        ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));
    }

    public IEnumerable GetErrors(string propertyName)
    {
        return TryGetValue(propertyName, out var value) ? value : null;
    }

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

        if (this[propertyName].Contains(error))
            return;

        this[propertyName].Add(error);
        OnErrorsChanged(propertyName);
    }

    public void ClearErrors(string propertyName)
    {
        if (!ContainsKey(propertyName))
            return;

        Remove(propertyName);
        OnErrorsChanged(propertyName);
    }
}