下面就为您介绍C#实现上传下载图片的完整攻略。

1. 上传图片

1.1 上传图片的基本原理

上传图片其实是将本地计算机的图片文件传输到服务器上。由于HTTP协议是无状态的，因此可以使用POST请求将文件传输到服务器上。

1.2 上传图片的技术实现

在C#中进行上传图片的技术实现，可以通过以下步骤完成：

1.2.1 选择需要上传的图片文件

使用OpenFileDialog控件选择需要上传的图片文件，并获取图片文件的本地路径。

OpenFileDialog dialog = new OpenFileDialog();
dialog.Filter = "图片文件|*.jpg;*.gif;*.png";
if (dialog.ShowDialog() == DialogResult.OK)
{
    string imagePath = dialog.FileName;
}

1.2.2 将图片文件以二进制流的形式进行上传

使用HttpWebRequest对象，构造POST请求，并设置请求头信息，将本地图片文件以二进制流的形式上传到服务器上。

string url = "http://localhost:8080/upload";
string imagePath = "D:\\test.jpg";
string boundary = "----" + DateTime.Now.Ticks.ToString("x");

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.ContentType = "multipart/form-data; boundary=" + boundary;

// 设置请求头信息
StringBuilder headerBuilder = new StringBuilder();
headerBuilder.AppendLine("--" + boundary);
headerBuilder.AppendLine("Content-Disposition: form-data; name=\"imageFile\"; filename=\"" + Path.GetFileName(imagePath) + "\"");
headerBuilder.AppendLine("Content-Type: application/octet-stream");
headerBuilder.AppendLine();

byte[] headerBytes = Encoding.UTF8.GetBytes(headerBuilder.ToString());
byte[] footerBytes = Encoding.UTF8.GetBytes("--" + boundary + "--\r\n");

// 构造二进制流
using (Stream requestStream = request.GetRequestStream())
{
    requestStream.Write(headerBytes, 0, headerBytes.Length);

    using (FileStream fileStream = new FileStream(imagePath, FileMode.Open, FileAccess.Read))
    {
        byte[] buffer = new byte[1024 * 1024];
        int readLength = 0;
        while ((readLength = fileStream.Read(buffer, 0, buffer.Length)) > 0)
        {
            requestStream.Write(buffer, 0, readLength);
        }
    }

    requestStream.Write(footerBytes, 0, footerBytes.Length);
}

// 获取服务器返回信息
using (WebResponse response = request.GetResponse())
{
    using (Stream responseStream = response.GetResponseStream())
    {
        using (StreamReader responseReader = new StreamReader(responseStream, Encoding.UTF8))
        {
            string responseText = responseReader.ReadToEnd();
        }
    }
}

1.3 上传图片的实例

下面是一个上传图片的示例：

private void UploadButton_Click(object sender, EventArgs e)
{
    OpenFileDialog dialog = new OpenFileDialog();
    dialog.Filter = "图片文件|*.jpg;*.gif;*.png";
    if (dialog.ShowDialog() == DialogResult.OK)
    {
        string url = "http://localhost:8080/upload";
        string imagePath = dialog.FileName;
        string boundary = "----" + DateTime.Now.Ticks.ToString("x");

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.Method = "POST";
        request.ContentType = "multipart/form-data; boundary=" + boundary;

        StringBuilder headerBuilder = new StringBuilder();
        headerBuilder.AppendLine("--" + boundary);
        headerBuilder.AppendLine("Content-Disposition: form-data; name=\"imageFile\"; filename=\"" + Path.GetFileName(imagePath) + "\"");
        headerBuilder.AppendLine("Content-Type: application/octet-stream");
        headerBuilder.AppendLine();

        byte[] headerBytes = Encoding.UTF8.GetBytes(headerBuilder.ToString());
        byte[] footerBytes = Encoding.UTF8.GetBytes("--" + boundary + "--\r\n");

        using (Stream requestStream = request.GetRequestStream())
        {
            requestStream.Write(headerBytes, 0, headerBytes.Length);

            using (FileStream fileStream = new FileStream(imagePath, FileMode.Open, FileAccess.Read))
            {
                byte[] buffer = new byte[1024 * 1024];
                int readLength = 0;
                while ((readLength = fileStream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    requestStream.Write(buffer, 0, readLength);
                }
            }

            requestStream.Write(footerBytes, 0, footerBytes.Length);
        }

        using (WebResponse response = request.GetResponse())
        {
            using (Stream responseStream = response.GetResponseStream())
            {
                using (StreamReader responseReader = new StreamReader(responseStream, Encoding.UTF8))
                {
                    string responseText = responseReader.ReadToEnd();
                }
            }
        }
    }
}

2. 下载图片

2.1 下载图片的基本原理

下载图片其实是将服务器上的图片文件下载到本地计算机。由于HTTP协议是无状态的，因此可以使用GET请求将服务器上的文件传输到本地计算机上。

2.2 下载图片的技术实现

在C#中进行下载图片的技术实现，可以通过以下步骤完成：

2.2.1 获取服务器图片文件的基本信息

使用HttpWebRequest对象，构造GET请求，并获取服务器图片文件的基本信息，例如文件名、文件类型等。

string imageUrl = "http://localhost:8080/images/test.jpg";

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(imageUrl);
request.Method = "HEAD";
using (WebResponse response = request.GetResponse())
{
    string fileName = response.Headers["Content-Disposition"].Substring(response.Headers["Content-Disposition"].IndexOf("=") + 1);
    string fileType = response.ContentType;
    long fileSize = response.ContentLength;
}

2.2.2 将图片文件以二进制流的形式进行下载

使用HttpWebRequest对象，构造GET请求，并以二进制流的形式下载服务器上的图片文件。

string imageUrl = "http://localhost:8080/images/test.jpg";

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(imageUrl);
request.Method = "GET";
using (WebResponse response = request.GetResponse())
{
    using (Stream responseStream = response.GetResponseStream())
    {
        using (MemoryStream memoryStream = new MemoryStream())
        {
            byte[] buffer = new byte[1024 * 1024];
            int readLength = 0;
            while ((readLength = responseStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                memoryStream.Write(buffer, 0, readLength);
            }

            byte[] imageBytes = memoryStream.ToArray();
        }
    }
}

2.3 下载图片的实例

下面是一个下载图片的示例：

private void DownloadButton_Click(object sender, EventArgs e)
{
    string imageUrl = "http://localhost:8080/images/test.jpg";

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(imageUrl);
    request.Method = "HEAD";
    using (WebResponse response = request.GetResponse())
    {
        string fileName = response.Headers["Content-Disposition"].Substring(response.Headers["Content-Disposition"].IndexOf("=") + 1);
        string fileType = response.ContentType;
        long fileSize = response.ContentLength;

        request = (HttpWebRequest)WebRequest.Create(imageUrl);
        request.Method = "GET";
        using (WebResponse imageResponse = request.GetResponse())
        {
            using (Stream responseStream = imageResponse.GetResponseStream())
            {
                using (MemoryStream memoryStream = new MemoryStream())
                {
                    byte[] buffer = new byte[1024 * 1024];
                    int readLength = 0;
                    while ((readLength = responseStream.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        memoryStream.Write(buffer, 0, readLength);
                    }

                    byte[] imageBytes = memoryStream.ToArray();

                    using (SaveFileDialog dialog = new SaveFileDialog())
                    {
                        dialog.FileName = fileName;
                        dialog.Filter = fileType + "|*" + Path.GetExtension(fileName);

                        if (dialog.ShowDialog() == DialogResult.OK)
                        {
                            using (FileStream fileStream = new FileStream(dialog.FileName, FileMode.Create))
                            {
                                fileStream.Write(imageBytes, 0, imageBytes.Length);
                            }
                        }
                    }
                }
            }
        }
    }
}

以上就是C#实现上传下载图片的完整攻略，希望能对您有所帮助。

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C#实现上传下载图片