Creating the models

Come back to the MvvmCrossDemo.Core project. You might be familiar with how to create a POCO model. I prefer to create a BaseResponseMessage to encapsulate the real Response Model Message for the UI layer, so it can make it easier to deal with some unexpected response message, such as null, or the other HTTP Status.

Add a folder called Models to the root folder of the MvvmCrossDemo.Core project and create a new file called BaseResponseMessage.cs into the Models folder, which looks like this:

namespace MvvmCrossDemo.Core.Models
{
    public class BaseResponseMessage
    {
        public bool IsSuccess { get; set; }
        public string Message { get; set; }
    }

    public class ResponseMessage<T> : BaseResponseMessage
    {
        public T Result { get; set; }
    }
}

The BaseResponseMessage is used to represent the result of some operations, such as Delete, because it contains no real entity in the response content. ResponseMessage will contain a real model entity so we can get it if the IsSuccess property is True, otherwise, we should show some messages to the users.

To deserialize the JSON data, we also need to add the reference to Newtonsoft.Json the NuGet Package Manager or input the command in the Package Manager Console:

Install-Package Newtonsoft.Json

Then we can add the real model class. Create a new class called Post.cs into the Models folder, which is shown as below:

using Newtonsoft.Json;

namespace MvvmCrossDemo.Core.Models
{
    public class Post
    {
        [JsonProperty("userId")]
        public int UserId { get; set; }

        [JsonProperty("id")]
        public int Id { get; set; }

        [JsonProperty("title")]
        public string Title { get; set; }

        [JsonProperty("body")]
        public string Body { get; set; }
    }
}

It is a common function to serizlize an object to JSON string or deserialize a JSON string to an object. Also, when we send the requests to the APIs, we need to convert the object to HttpContent. we can create some extension methods to simplify this process. Create a new folder called Infrastructure into the root folder of the MvvmCrossDemo.Core project and create a folder named Extensions into the Infrastructure folder. Then add a new file called JsonExtentions.cs file in to the Extensions folder. Replace the default content with these codes:

using Newtonsoft.Json;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace MvvmCrossDemo.Core.Infrastructure.Extensions
{
    public static class JsonExtensions
    {
        public static async Task<T> ReadAsJsonAsync<T>(this HttpResponseMessage response)
        {
            string jsonString = await response.Content.ReadAsStringAsync();
            return jsonString.ToObject<T>();
        }

        public static T ToObject<T>(this string jsonString)
        {
            return JsonConvert.DeserializeObject<T>(jsonString);
        }

        public static StringContent ToStringContent<T>(this T obj)
        {
            return ToStringContent(obj, "application/json");
        }

        public static StringContent ToStringContent<T>(this T obj, string contentType)
        {
            string json = JsonConvert.SerializeObject(obj);
            return new StringContent(json, Encoding.UTF8, contentType);
        }
    }
}