How do I properly use async and await in this code?

My Windows Form application freezes when deserializing "all episodes" from a local XML-file. I want to solve this problem by implementing asynchronous programming but unfortunately I do not succeed with the implementation (I am a beginner and it's the first time I use await and async).

Working (but freezing) synchronous execution:

public class EpisodeRepository : IEpisodeRepository<Episode>
{
    SerializerForXml dataManager;
    List<Episode> listOfEpisodes;
    
    public EpisodeRepository()
    {
        dataManager = new SerializerForXml();
        listOfEpisodes = new List<Episode>();
        listOfEpisodes = GetAll();
    }
    public List<Episode> GetAll()
    {
        List<Episode> listOfEpisodesDeserialized = new List<Episode>();
        try
        {
            listOfEpisodesDeserialized = dataManager.DeserializeEpisode());
        }
        catch (Exception)
        {
            throw new SerializerException("Episode.xml", "Error when deserialize");
        }

        return listOfEpisodesDeserialized;
    } 
}
public interface IEpisodeRepository<T> : IRepository<T> where T : class
{
    List<T> GetAllFeed(string url);
}

public interface IRepository<T> where T : class
{
    void Create(T entity);
    void Delete(int index);
    void Update(int index, T entity);
    void SaveChanges();
    List<T> GetAll();
    int GetIndex(string name);
}

My attempt to solve it with async and await:

I changed the interface method in IRepository to Task<List<T>> GetAll(); and then I changed the method to:

public async Task<List<Episode>> GetAll()
        {
            List<Episode> listOfEpisodesDeserialized = new List<Episode>();
            try
            {
                listOfEpisodesDeserialized  = await Task.Run(() => dataManager.DeserializeEpisode());
            }
            catch (Exception)
            {
                throw new SerializerException("Episode.xml", "Error when deserialize");
            }

            return listOfEpisodesDeserialized;
        } 

This code won't compile because the method returns

"System.Threading.Tasks.Task<System.Collections.Generic.List<Models.Episode>>" when the field is of type "System.Collections.Generic.List<Models.Episode>".

This code also causes some errors to other methods using GetAll().FirstOrDefault(..).

from Recent Questions - Stack Overflow https://ift.tt/3meu9Nz
https://ift.tt/eA8V8J