Windows Forms: Consume Web API In Winform For File Handling in C#

First, You need to know how to create a Web API to help you upload files to a web server. If you don't know how to Create a Web API in Visual Studio you can view this post: How to Upload files in ASP.NET Core Web API using C#.

Creating a new Windows Forms Application, then drag Label, TextBox and Button controls from the Visual Studio Toolbox to your form designer. You can create a simple UI that allows you to select a file, then upload it to web server via web api in c#.

Creating an UploadAsync method allows you to upload the file to the web server by calling web api controller in c# windows forms application.

private async Task<HttpResponseMessage> UploadAsync(string fileName, string server)
{
    using (var fileStream = File.Open(txtFileName.Text, FileMode.Open))
    {
        using (MemoryStream memoryStream = new MemoryStream())
        {
            await fileStream.CopyToAsync(memoryStream);
            using (MultipartFormDataContent multipartFormDataContent = new MultipartFormDataContent())
            {
                multipartFormDataContent.Add(new ByteArrayContent(memoryStream.ToArray()), "file", txtFileName.Text);
                using (var client = new HttpClient())
                {
                    var response = await client.PostAsync(server, multipartFormDataContent).ConfigureAwait(false);
                    return response;
                }
            }
        }
    }
}

Adding a click event handler to the Browse button allows you to open a file dialog box, then select the file and update the file name to the TextBox control.

private void btnBrowse_Click(object sender, EventArgs e)
{
    using (OpenFileDialog ofd = new OpenFileDialog() { Filter = "All files|*.*" })
    {
        if (ofd.ShowDialog() == DialogResult.OK)
            txtFileName.Text = ofd.FileName;
    }
}

Finally, Add a click event handler to the Upload button allows you to call the UploadAsync method to upload files from your hard drive to the web server using web api in c# windows forms application.

private async void btnUpload_Click(object sender, EventArgs e)
{
    if (!string.IsNullOrEmpty(txtFileName.Text))
    {
        string url = "http://localhost:11122/api/file/upload";
        HttpResponseMessage responseMessage = await this.UploadAsync(txtFileName.Text, url);
        if (responseMessage.StatusCode == System.Net.HttpStatusCode.OK)
            MessageBox.Show("You have successfully uploaded the file", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
}

You can easily upload images or any other files to the web server using the UploadAsync method to upload files via web api in c#.