從.NET/C中的網站下載圖像＃

Question

我想從網站下載圖像。我使用的代碼在圖像可用時工作正常。如果圖片不可用，則會造成問題。如何驗證圖像的可用性？

代碼：

方法1：

WebRequest requestPic = WebRequest.Create(imageUrl); 

WebResponse responsePic = requestPic.GetResponse(); 

Image webImage = Image.FromStream(responsePic.GetResponseStream()); // Error 

webImage.Save("D:\\Images\\Book\\" + fileName + ".jpg"); 

方法2：

WebClient client = new WebClient(); 
Stream stream = client.OpenRead(imageUrl); 

bitmap = new Bitmap(stream); // Error : Parameter is not valid. 
stream.Flush(); 
stream.Close(); 
client.dispose(); 

if (bitmap != null) 
{ 
    bitmap.Save("D:\\Images\\" + fileName + ".jpg"); 
} 

編輯：

流具有下面的語句：

 Length '((System.Net.ConnectStream)(str)).Length' threw an exception of type 'System.NotSupportedException' long {System.NotSupportedException} 
    Position '((System.Net.ConnectStream)(str)).Position' threw an exception of type 'System.NotSupportedException' long {System.NotSupportedException} 
ReadTimeout 300000 int 
WriteTimeout 300000 int 

Answer 1

沒有必要讓任何圖像類，你可以簡單地調用WebClient.DownloadFile：

string localFilename = @"c:\localpath\tofile.jpg"; 
using(WebClient client = new WebClient()) 
{ 
    client.DownloadFile("http://www.example.com/image.jpg", localFilename); 
} 

---

更新
既然你要檢查文件是否存在，下載文件如果是這樣，最好在相同的請求內完成此操作。因此，這裏是一個方法，將做到這一點：

private static void DownloadRemoteImageFile(string uri, string fileName) 
{ 
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); 
    HttpWebResponse response = (HttpWebResponse)request.GetResponse(); 

    // Check that the remote file was found. The ContentType 
    // check is performed since a request for a non-existent 
    // image file might be redirected to a 404-page, which would 
    // yield the StatusCode "OK", even though the image was not 
    // found. 
    if ((response.StatusCode == HttpStatusCode.OK || 
     response.StatusCode == HttpStatusCode.Moved || 
     response.StatusCode == HttpStatusCode.Redirect) && 
     response.ContentType.StartsWith("image",StringComparison.OrdinalIgnoreCase)) 
    { 

     // if the remote file was found, download oit 
     using (Stream inputStream = response.GetResponseStream()) 
     using (Stream outputStream = File.OpenWrite(fileName)) 
     { 
      byte[] buffer = new byte[4096]; 
      int bytesRead; 
      do 
      { 
       bytesRead = inputStream.Read(buffer, 0, buffer.Length); 
       outputStream.Write(buffer, 0, bytesRead); 
      } while (bytesRead != 0); 
     } 
    } 
} 

簡單地說，它使文件的請求，驗證響應代碼是OK，Moved或Redirect之一，也是了ContentType是圖片。如果這些條件成立，則文件被下載。

Answer 2

我在稍作修改項目中使用上述弗雷德裏克的代碼，想我會分享：

private static bool DownloadRemoteImageFile(string uri, string fileName) 
{ 
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); 
    HttpWebResponse response; 
    try 
    { 
     response = (HttpWebResponse)request.GetResponse(); 
    } 
    catch (Exception) 
    { 
     return false; 
    } 

    // Check that the remote file was found. The ContentType 
    // check is performed since a request for a non-existent 
    // image file might be redirected to a 404-page, which would 
    // yield the StatusCode "OK", even though the image was not 
    // found. 
    if ((response.StatusCode == HttpStatusCode.OK || 
     response.StatusCode == HttpStatusCode.Moved || 
     response.StatusCode == HttpStatusCode.Redirect) && 
     response.ContentType.StartsWith("image", StringComparison.OrdinalIgnoreCase)) 
    { 

     // if the remote file was found, download it 
     using (Stream inputStream = response.GetResponseStream()) 
     using (Stream outputStream = File.OpenWrite(fileName)) 
     { 
      byte[] buffer = new byte[4096]; 
      int bytesRead; 
      do 
      { 
       bytesRead = inputStream.Read(buffer, 0, buffer.Length); 
       outputStream.Write(buffer, 0, bytesRead); 
      } while (bytesRead != 0); 
     } 
     return true; 
    } 
    else 
     return false; 
} 

主要變化如下：

• 使用try/catch語句的的GetResponse（ ），因爲我在遠程文件返回時遇到異常404
• 返回布爾值

Answer 3

 private static void DownloadRemoteImageFile(string uri, string fileName) 
     { 
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); 
      HttpWebResponse response = (HttpWebResponse)request.GetResponse(); 

      if ((response.StatusCode == HttpStatusCode.OK || 
       response.StatusCode == HttpStatusCode.Moved || 
       response.StatusCode == HttpStatusCode.Redirect) && 
       response.ContentType.StartsWith("image", StringComparison.OrdinalIgnoreCase)) 
      { 
       using (Stream inputStream = response.GetResponseStream()) 
       using (Stream outputStream = File.OpenWrite(fileName)) 
       { 
        byte[] buffer = new byte[4096]; 
        int bytesRead; 
        do 
        { 
         bytesRead = inputStream.Read(buffer, 0, buffer.Length); 
         outputStream.Write(buffer, 0, bytesRead); 
        } while (bytesRead != 0); 
       } 
      } 
     } 

Answer 4

也可以使用DownloadData方法

private byte[] GetImage(string iconPath) 
    { 
     using (WebClient client = new WebClient()) 
     { 
      byte[] pic = client.DownloadData(iconPath); 
      //string checkPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) +@"\1.png"; 
      //File.WriteAllBytes(checkPath, pic); 
      return pic; 
     } 
    }