如何識別文件是否存在於我的網絡服務器文件夾或沒有在android系統

Question

背景：

我有一個顯示在Android從Web服務器的一些圖像的典型要求。網絡服務器中的所有圖像都是按順序編號的，我現在可以在android中顯示圖片。

問題： 是否有可能確定圖像是否存在於網絡服務器？如果沒有圖像，然後我得到沒有圖像和它沒有顯示我的錯誤

代碼：

公共類ImageViewFromURLActivity延伸活動{

public static final String URL = 
    "http://mywebsite.com/private/image1.jpg"; //this is just an example 
ImageView imageView; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    imageView = (ImageView) findViewById(R.id.imageView); 

    // Create an object for subclass of AsyncTask 
    GetXMLTask task = new GetXMLTask(); 
    // Execute the task 
    task.execute(new String[] { URL }); 
} 

private class GetXMLTask extends AsyncTask<String, Void, Bitmap> { 
    @Override 
    protected Bitmap doInBackground(String... urls) { 
     Bitmap map = null; 
     for (String url : urls) { 
      map = downloadImage(url); 
     } 
     return map; 
    } 

    // Sets the Bitmap returned by doInBackground 
    @Override 
    protected void onPostExecute(Bitmap result) { 
     imageView.setImageBitmap(result); 
    } 

    // Creates Bitmap from InputStream and returns it 
    private Bitmap downloadImage(String url) { 
     Bitmap bitmap = null; 
     InputStream stream = null; 
     BitmapFactory.Options bmOptions = new BitmapFactory.Options(); 
     bmOptions.inSampleSize = 1; 

     try { 
      stream = getHttpConnection(url); 
      bitmap = BitmapFactory. 
        decodeStream(stream, null, bmOptions); 
      stream.close(); 
     } catch (IOException e1) { 
      e1.printStackTrace(); 
     } 
     return bitmap; 
    } 

    // Makes HttpURLConnection and returns InputStream 
    private InputStream getHttpConnection(String urlString) 
      throws IOException { 
     InputStream stream = null; 
     URL url = new URL(urlString); 
     URLConnection connection = url.openConnection(); 

     try { 
      HttpURLConnection httpConnection = (HttpURLConnection) connection; 
      httpConnection.setRequestMethod("GET"); 
      httpConnection.connect(); 

      if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) { 
       stream = httpConnection.getInputStream(); 
      } 
     } catch (Exception ex) { 
      ex.printStackTrace(); 
     } 
     return stream; 
    } 
} 

}

Answer 1

你可以使用JavaScript和Image.onload事件來確定圖像是否可以加載。

實施例：

var img = new Image; 
img.onerror = function() { 
    // you can also do something in the error event handler 
} 
img.onload = function() { 
    // display the image via JS here. 
} 
img.src = 'path/to/file';