Using HttpClient in C# to Send POST and GET Requests to Call APIs

In modern application development, interacting with Web APIs is a fundamental skill. This article will introduce how to use the HttpClient class in C# to send POST and GET requests to call external API services.

Introduction to HttpClient

HttpClient is a class in the .NET Framework and .NET Core used for sending HTTP requests and receiving HTTP responses. It supports asynchronous operations and can efficiently handle web requests, making it the preferred way for modern C# applications to interact with web services.

1. Preparation

1. Prepare anAPI request URL: https://api.qqsuu.cn/api/dm-caipuRequest method: Both GET and POST are acceptable2. Create a Windows Forms application project. In Visual Studio 2019:

1. Create a new Windows Forms App (.NET Framework) project

2. Name it “WindowsFormsHttpClient“

3. Design a simple interface that includes:

• A text box (textBox1) for entering query parameters

• Two buttons (button1 and button2) to trigger POST and GET requests respectively

• A rich text box (richTextBox1) to display the API response results

2. Implementation of GET Request

The GET request is used to retrieve data from the server. In our example, the <span><span>Get</span></span> method implements the basic functionality of a GET request:

1. Create an instance of HttpClient (using the using statement to ensure resource release)

2. Call the <span><span>GetAsync</span></span> method to send the request

3. Use <span><span>EnsureSuccessStatusCode</span></span> to check the response status code

4. Read the response content

        public async Task<string> Get(string strUrl)        {            string str_Output = "";            try            {                using (HttpClient client = new HttpClient())                {                    HttpResponseMessage response = await client.GetAsync(strUrl);                    response.EnsureSuccessStatusCode(); // If the status code is not successful, an exception will be thrown                    str_Output = await response.Content.ReadAsStringAsync();                    return str_Output;                }            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }

3. Implementation of POST Request

The POST request is typically used to submit data to the server. Our <span><span>Post</span></span> method implements the basic functionality of a POST request:

        public async Task<string> Post(string strUrl)        {            string str_Output = "";            try            {                using (HttpClient client = new HttpClient())                {                    HttpResponseMessage response = await client.PostAsync(strUrl, null);                    response.EnsureSuccessStatusCode();                    str_Output = await response.Content.ReadAsStringAsync();                    return str_Output;                }            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }

Note that in this simple example, we passed <span><span>null</span></span> as the POST content. In practical applications, you may need to send JSON, form data, or other formats of content.

4. Complete Code

        private async void button1_Click(object sender, EventArgs e)        {            string strUrl = "https://api.qqsuu.cn/api/dm-caipu?word=" + textBox1.Text.Trim();            string strReturn = await Post(strUrl);            richTextBox1.Text = strReturn;        }        private async void button2_Click(object sender, EventArgs e)        {            string strUrl = "https://api.qqsuu.cn/api/dm-caipu?word=" + textBox1.Text.Trim();            string strReturn = await Get(strUrl);            richTextBox1.Text = strReturn;        }        public async Task<string> Post(string strUrl)        {            string str_Output = "";            try            {                using (HttpClient client = new HttpClient())                {                    HttpResponseMessage response = await client.PostAsync(strUrl, null);                    response.EnsureSuccessStatusCode();                    str_Output = await response.Content.ReadAsStringAsync();                    return str_Output;                }            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }        public async Task<string> Get(string strUrl)        {            string str_Output = "";            try            {                using (HttpClient client = new HttpClient())                {                    HttpResponseMessage response = await client.GetAsync(strUrl);                    response.EnsureSuccessStatusCode(); // If the status code is not successful, an exception will be thrown                    str_Output = await response.Content.ReadAsStringAsync();                    return str_Output;                }            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }

Effect:

4. Best Practices

1. Reuse HttpClient instances: Reusing HttpClient instances throughout the application lifecycle, rather than creating a new instance for each request, can improve performance.

2. Set request timeouts: Set reasonable timeout periods for HttpClient:

client.Timeout = TimeSpan.FromSeconds(30);

3. Add request headers: Many APIs require specific request headers:

client.DefaultRequestHeaders.Add("Authorization", "Bearer your_token");

4. Handle JSON responses: Use Newtonsoft.Json or System.Text.Json to handle JSON responses:

var result = JsonConvert.DeserializeObject<MyModel>(responseContent);

5.Send JSON content:

var content = new StringContent(JsonConvert.SerializeObject(data), Encoding.UTF8, "application/json");var response = await client.PostAsync(url, content);

5. Extensions

1. Send a POST request with parameters

        public async Task<string> PostJson(string strUrl, string jsonInput)        {            string str_Output = "";            try            {                using (HttpClient client = new HttpClient())                {                    var content = new StringContent(jsonInput, Encoding.UTF8, "application/json");                    HttpResponseMessage response = await client.PostAsync(strUrl, content);                    response.EnsureSuccessStatusCode();                    str_Output = await response.Content.ReadAsStringAsync();                    return str_Output;                }            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }

2. Send a DELETE request with parameters

       public async Task<bool> DeleteJson(string strUrl, string jsonInput)        {            try            {                using (HttpClient client = new HttpClient())                {                    var request = new HttpRequestMessage                    {                        Method = HttpMethod.Delete,                        RequestUri = new Uri(strUrl),                        Content = new StringContent(jsonInput, Encoding.UTF8, "application/json")                    };                    HttpResponseMessage response = await client.SendAsync(request);                    response.EnsureSuccessStatusCode();                    return true;                }            }            catch (Exception ex)            {                return false;            }        }

3. Send a GET request with headers

        public async Task<string> GetHeaders(string url)        {            using (HttpClient client = new HttpClient())            {                client.DefaultRequestHeaders.Add("Authorization", "Bearer your_token_here");                client.DefaultRequestHeaders.Add("Custom-Header", "Value");                HttpResponseMessage response = await client.GetAsync(url);                response.EnsureSuccessStatusCode();                return await response.Content.ReadAsStringAsync();            }        }

Conclusion

This article introduced the basic methods of using HttpClient in C# to send POST and GET requests. Key points include:

1. Using the <span><span>HttpClient</span></span> class to send HTTP requests

2. Asynchronous programming model (async/await)

3. Basic error handling

4. Response status code checking

5. Reading response content

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