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EdurdoSwolano
Asked: 2020-08-31 09:04:14 +0800 CST 2020-08-31 09:04:14 +0800 CST

Problem with singleton and a rest api in Xamarin

  • 772

I am working on an application with xamarin forms cross platform, well I am using a menu whose information is obtained from a rest api, to avoid that each time a call is made to the menu an api query is made I decided to use a singleton, however It does not return the data from the api, it is worth mentioning that if I do not use the singleton it does bring the data. The code looks like this

Model-CategoriesModel

 public partial class CategoriesModel
{
    [JsonProperty("id")]
    public long Id { get; set; }

    [JsonProperty("parent_id")]
    public long ParentId { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("is_active")]
    public bool IsActive { get; set; }

    [JsonProperty("position")]
    public long Position { get; set; }

    [JsonProperty("level")]
    public long Level { get; set; }

    [JsonProperty("product_count")]
    public long ProductCount { get; set; }

    [JsonProperty("children_data")]
    public List<CategoriesModel> ChildrenData { get; set; }
}

public partial class CategoriesModel
{
    public static CategoriesModel FromJson(string json) => JsonConvert.DeserializeObject<CategoriesModel>(json, PetandLove.Model.Converter.Settings);
}

I have a ViewModel that makes the query even in api rest that is in a different class. ViewModel- MenuSpeciesViewModel

 ConectionApiMagento category = new ConectionApiMagento();
   public CategoriesModel categoryModel { get; set;}

    public MenuEspeciesViewModel()
    {
        getCategory();
    }

    public async void getCategory()
    {
        categoryModel = await category.GetCategories();
    }

Class that makes the connection- ConectionApiMagento.cs

public class ConectionApiMagento
{
    static readonly HttpClient cliente = new HttpClient();
    public async Task<CategoriesModel> GetCategories()
    {
            string url = "url";
            var resultado = await cliente.GetAsync(url);
            var json = resultado.Content.ReadAsStringAsync().Result;

            CategoriesModel item = CategoriesModel.FromJson(json);
            return item;
    }
}

Singleton

public  class MenuSinlgeton
{

    #region Properties

    private static MenuSinlgeton _instance = null;
    public MenuEspeciesViewModel Especies { get; set;} 
    #endregion

    public  MenuSinlgeton()
    {
        Especies = new MenuEspeciesViewModel();
    }
    #region methods
    internal static MenuSinlgeton Instance()
    {
        if (_instance==null)
        {
            _instance = new MenuSinlgeton();
        }
        return _instance;
    }

    #endregion
}

The call to the singleton is made in the app.xmal.cs constructor and in the class where the data is drawn. I use this call. MenuSinlgeton Especies = MenuSinlgeton.Instance(); In essence I would like the singleton to have the data that the api returns so that I can use it an infinite number of times with just one api call, I don't get errors only when I try to use the data that the singleton is supposed to bring.

xamarin

1 Answers

  1. Best Answer

    I took the liberty of modifying your code to make it work. I hope it helps you or at least to take it as a guide for a solution.

    public class MenuSinlgeton
{
    public CategoriesModel CategoryModel { get; }

    private static MenuSinlgeton _instance = null;
    public MenuSinlgeton(CategoriesModel categoryModel)
    {
        CategoryModel = categoryModel;
    }

    public static MenuSinlgeton Instance()
    {
        if (_instance == null)
        {
            ConectionApiMagento cnn = new ConectionApiMagento();

            //////////////////////////////////////////////////////////////////////////////////////////////////
            //El motivo de este codigo es porque se esta llamando a un metodo async dentro de uno NO async
            var categorias = Task.Run(async () => await cnn.GetCategories());
            categorias.Wait(new TimeSpan(0, 0, 15));
            //////////////////////////////////////////////////////////////////////////////////////////////////

            _instance = new MenuSinlgeton(categorias.Result);
        }
        return _instance;
    }

    public class ConectionApiMagento
    {
        static readonly HttpClient cliente = new HttpClient();
        public async Task<CategoriesModel> GetCategories()
        {
            string url = "https://url.com/endpoint/?parameter=6";
            var resultado = await cliente.GetAsync(url);
            var json = resultado.Content.ReadAsStringAsync().Result;

            CategoriesModel item = CategoriesModel.FromJson(json);
            return item;
        }
    }
}

    Then you can make the call

    MenuSinlgeton Especies = MenuSinlgeton.Instance();
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