Building a REST API Client in C# with Windows Form

byMarianz -
0

 



In this tutorial, we'll build a simple C# Windows Forms application that connects to a REST API. Our goal is to interact with the products API endpoints we created earlier, using HTTP requests to view, add, update, and delete product records. This tutorial is beginner-friendly and demonstrates how to use HttpClient in C# to communicate with RESTful services. Before diving into this tutorial, it's essential to complete our previous tutorial on creating a REST API using native PHP as a server-side foundation. In that guide, we built a simple REST API to manage products and categories, covering basic API endpoints like creating, updating, deleting, and retrieving product records.

Prerequisites

  • A basic understanding of C# and Windows Forms.
  • Visual Studio installed on your machine.
  • The REST API from the previous tutorial (running locally or on a server).

Project Setup

    1. Create a new Windows Forms App in Visual Studio. Open Visual Studio, select Create a new project, and choose Windows Forms App (.NET Framework).

    2. Set up UI elements. Design the form with input fields for ID, Name, Description, and Price, as well as buttons for CRUD operations (Get, Create, Update, Delete). Here’s a sample layout:
    • TextBox for ID
    • TextBox for Name
    • TextBox for Description
    • TextBox for Price
    • Buttons labeled Get, Create, Update, and Delete
    • ListBox or DataGridView to display product data
    3. In your project, create a Product class to hold the product data. This class will be used to serialize and deserialize JSON.
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public decimal Price { get; set; }
}

    4. Create a ApiResponse Class to represent the JSON response structure. This class will be used on message handling of some responses.
public class ApiResponse
{
    public string Message { get; set; }
}


Adding Code for API Calls

    1. Add necessary using statements at the top of your code:
using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Windows.Forms;
using Newtonsoft.Json;
using System.Collections.Generic;

Note: You’ll need to install Newtonsoft.Json from NuGet to handle JSON serialization and deserialization.

    2. Initialize HttpClient. We’ll set up HttpClient as a static client to make HTTP requests to the API.
private static readonly HttpClient client = new HttpClient();

    3. Define the API URL (change localhost to your API’s address if it’s running on a server).
private readonly string apiUrl = "http://localhost/api/products";
//private readonly string apiUrl = "https://bcssti.com/api-sample/products/";

Implementing CRUD Operations

1. Get Products (GET)

This method fetches the list of all products from the API and displays them in a ListView or DataGridView.

private async void GetProducts()
{
    try
    {
        var response = await client.GetAsync(apiUrl);
        response.EnsureSuccessStatusCode();
        var responseBody = await response.Content.ReadAsStringAsync();
        var products = JsonConvert.DeserializeObject<List<Product>>(responseBody);

        // Display the products in a ListView or DataGridView
        productListBox.DataSource = products;
        productListBox.DisplayMember = "Name"; // Display name or other relevant info
    }
    catch (Exception ex)
    {
        MessageBox.Show($"Error: {ex.Message}");
    }
}

2. Get Product by ID (GET)

This method retrieves a single product based on its ID.

private async void GetProductById(int id)
{
    try
    {
        var response = await client.GetAsync($"{apiUrl}?id={id}");
        response.EnsureSuccessStatusCode();
        var responseBody = await response.Content.ReadAsStringAsync();
        var product = JsonConvert.DeserializeObject<Product>(responseBody);

        // Populate fields with product data
        txtName.Text = product.Name;
        txtDescription.Text = product.Description;
        txtPrice.Text = product.Price.ToString();
    }
    catch (Exception ex)
    {
        MessageBox.Show($"Error: {ex.Message}");
    }
}

3. Create Product (POST)

This method sends a new product to the API.

private async void CreateProduct()
{
    dynamic product = new 
    {
        name = txtName.Text,
        description = txtDescription.Text,
        price = decimal.Parse(txtPrice.Text)
    };

    var json = JsonConvert.SerializeObject(product);
    var content = new StringContent(json, Encoding.UTF8, "application/json");

    try
    {
        var response = await client.PostAsync(apiUrl, content);
        response.EnsureSuccessStatusCode();

        var responseBody = await response.Content.ReadAsStringAsync();
        var apiResponse = JsonConvert.DeserializeObject<ApiResponse>(responseBody);

        // Display the message from the API response
        MessageBox.Show(apiResponse.Message ?? "Product created successfully");
    }
    catch (Exception ex)
    {
        MessageBox.Show($"Error: {ex.Message}");
    }
}

4. Update Product (PUT)

This method updates an existing product.

private async void UpdateProduct(int id)
{
    dynamic product = new 
    {
        name = txtName.Text,
        description = txtDescription.Text,
        price = decimal.Parse(txtPrice.Text)
    };

    var json = JsonConvert.SerializeObject(product);
    var content = new StringContent(json, Encoding.UTF8, "application/json");

    try
    {
        var response = await client.PutAsync($"{apiUrl}?id={id}", content);
        response.EnsureSuccessStatusCode();

        var responseBody = await response.Content.ReadAsStringAsync();
        var apiResponse = JsonConvert.DeserializeObject<ApiResponse>(responseBody);

        // Display the message from the API response
        MessageBox.Show(apiResponse.Message ?? "Product updated successfully");
    }
    catch (Exception ex)
    {
        MessageBox.Show($"Error: {ex.Message}");
    }
}

5. Delete Product (DELETE)

This method deletes a product by ID.

private async void DeleteProduct(int id)
{
    try
    {
        var response = await client.DeleteAsync($"{apiUrl}?id={id}");
        response.EnsureSuccessStatusCode();

        var responseBody = await response.Content.ReadAsStringAsync();
        var apiResponse = JsonConvert.DeserializeObject<ApiResponse>(responseBody);

        // Display the message from the API response
        MessageBox.Show(apiResponse.Message ?? "Product deleted successfully");
    }
    catch (Exception ex)
    {
        MessageBox.Show($"Error: {ex.Message}");
    }
}

Testing the Application

  • Run the Windows Forms App in Visual Studio.
  • Use the Get button to list all products or retrieve a specific product by ID.
  • Use the Create, Update, and Delete buttons to interact with the API.

This setup provides a basic client interface for the products API. You can expand this application to manage other objects or add additional features like input validation and error handling.


Final Thoughts

Creating a client for your API in C# Windows Forms is a fantastic way to learn about HTTP communication and RESTful APIs. By using HttpClient and JSON serialization with Newtonsoft.Json, you can quickly set up a functional application to interact with any RESTful service.

This example demonstrates only the basics, but you can extend the client with additional features:

  • Pagination and Filtering: If your API supports it, implement controls for navigating through pages of data.
  • Advanced Error Handling: Customize error messages for various HTTP status codes.
  • UI Improvements: Use DataGridView for more complex data display and editing.

Experiment with these concepts to build a full-featured client for your REST API.

Tags

You may like these posts

Previous Post Next Post

نموذج الاتصال