Send a request to a restapi with json

Question

Do someone knows of a sample project with forms to send request to a RestAPI with tests?

Thanks

Claude from Quebec, Canada

Answer 1

Hi @Claude Larocque ,Welcome to Q&A.

You can use httpclient and System.Text.Json.

Here is a winform example I wrote (.Net Framework 4.8):

using System;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Windows.Forms;

namespace WindowsFormsApp2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private async void button1_Click(object sender, EventArgs e)
        {
            try
            {
                string url = "http://example.com/api/v1/resource";
                HttpClient client = new HttpClient();
                var requestData = new { key = "value" };
                string json = JsonSerializer.Serialize(requestData);
                var content = new StringContent(json, Encoding.UTF8, "application/json");
                var response = await client.PostAsync(url, content);
                string responseContent = await response.Content.ReadAsStringAsync();
                MessageBox.Show(responseContent);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}

There may be a lack of system.memory during operation. (Manually add it into the project)

Best Regards,

Jiale

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Answer 2

I have shared a step-by-step guide in stackoverflow that you can take a look: Call and Consume Rest APIs in Windows Forms

There's also a docs article on this topic: Call a Web API From a .NET Client.

Download the Example

Here in this post, I'll share one of my step-by-step examples which uses an online REST API service (https://northwind.vercel.app) which allows interaction with Northwind API. This example uses HttpClient and JsonConvert to get or post data:

If you want to jump to code, without reading the step-by-steo guide, you can clone or download example from here:

• Clone GitHub Repository: r-aghaei/WinFormsRestAPICall.git
• Download master.zip

Step by step example

1. Create a WinForms Application
2. Add a new class call it Category.cs, and use the following code for the class:

      public class Category
      {
          public int Id {get; set;}
          public string Name {get; set;}
          public string Description {get; set;}
      }
   

3. Drop a DataGridView on the form, let's use the default name dataGridView1.
4. Install Newtonsoft.Json nuget package. And add the following using statements to your form:

      using System.Net.Http;
      using Newtonsoft.Json;
   

5. Define an instance of the HttpClient, at class level:

      private static HttpClient client = new HttpClient();
   

6. To send a GET request, for example getting list of all data, assuming you have a dataGridView1 on the from, run the following code for example in Load event handler, double click on the Form to create the load handler, and use the following code:

      private async void Form1_Load(object sender, EventArgs e)
      {
          var url = "https://northwind.vercel.app/api/categories";
          var response = await client.GetAsync(url);
          if (response.StatusCode == System.Net.HttpStatusCode.OK)
          {
              var content = await response.Content.ReadAsStringAsync();
              var categories = JsonConvert.DeserializeObject<List<Category>>(content);
              dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
              dataGridView1.DataSource = categories;
          }
      }
   

   You can also use other overloads of Get, like GetStringAsync, GetStreamAsync, and etc. But GetAsync is a more generic method allowing you to get the status code as well.
7. To send a POST request, for example posting a new data, you can use the following code, for example in click event handler of a button or a ToolStripButton:

      private async void addToolStripButton_Click(object sender, EventArgs e)
      {
          var url = "https://northwind.vercel.app/api/categories";
          var data = new Category() { Name = "Lorem", Description = "Ipsum" };
          var jsonData = Newtonsoft.Json.JsonConvert.SerializeObject(data);
          var requestContent = new StringContent(jsonData, Encoding.Unicode, "application/json");
          var response = await client.PostAsync(url, requestContent);
          if (response.StatusCode == System.Net.HttpStatusCode.Created)
          {
              var content = await response.Content.ReadAsStringAsync();
              var createdCategory = JsonConvert.DeserializeObject<Category>(content);
              MessageBox.Show(createdCategory.Id.ToString());
          }
      }
   

To learn more and see some best practices or see an example without JsonConvert, see my stackoverflow post: Call and Consume Rest APIs in Windows Forms.