下载图像表单Web时,BitmapFactory.decodeStream返回null

Question

我正在尝试使用Google示例页面从网址下载图片.我在BitmapFactory.decodeStream方法中使用InputStream时读过,我不能使用两次.我试图这样做,但它不起作用'因为它在解码图像中返回null,我不知道我能做什么.

这是我的代码:

这部分是在AsyncTask类中的doInBackground方法中

Bitmap bitmapImage;
URL imageUrl = null;
try {
imageUrl = new URL(url[0]);

HttpGet httpRequest = null;
httpRequest = new HttpGet(imageUrl.toURI());

HttpClient httpclient = new DefaultHttpClient();
HttpResponse response = (HttpResponse) httpclient.execute(httpRequest);

HttpEntity entity = response.getEntity();
BufferedHttpEntity bufHttpEntity = new BufferedHttpEntity(entity);
InputStream instream = bufHttpEntity.getContent();

    bitmapImage = CommonMethods.decodeSampledBitmapFromResource(instream, thumb_width, thumb_width);

instream.close();
return bitmapImage;

 } catch (URISyntaxException e) {
    e.printStackTrace();
    return null;
 } catch (MalformedURLException e) {
    e.printStackTrace();
    return null;
 } catch (IOException e) {
    e.printStackTrace();
    return null;
 }


 public static Bitmap decodeSampledBitmapFromResource(InputStream instream,
        int reqWidth, int reqHeight) throws IOException {

    //Copy instream for decode twice 
ByteArrayOutputStream out = new ByteArrayOutputStream();
    copy(instream,out);
    ByteArrayInputStream instream2 = new ByteArrayInputStream(out.toByteArray());

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeStream(instream, null, options);
    instream2.close();

    options.inJustDecodeBounds = false;

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    return BitmapFactory.decodeStream(instream, null, options);
 }

 public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {

     // Raw height and width of image
     final int height = options.outHeight;
     final int width = options.outWidth;
     int inSampleSize = 1;

     if (height > reqHeight || width > reqWidth) {
         if (width > height) {
         inSampleSize = Math.round((float) height / (float) reqHeight);
     } else {
             inSampleSize = Math.round((float) width / (float) reqWidth);
     }
     }

     return inSampleSize;
}

//Copy instream method
public static void copy(InputStream input, OutputStream output) throws IOException{

     byte[] buffer = new byte[Constants.IO_BUFFER_SIZE];

 int n = 0;

 while (-1 != (n = input.read(buffer))) {

     output.write(buffer, 0, n);
 }
 }

Answer 1

BitmapFactory.decodeStream返回null,因为输入流被使用了两次,我没有尝试过你的代码,但它接缝正常,或者我错了.无论如何,我有一个更好的解决方案.只需使用BufferedInputStream包装inputStream,在第二次读取之前,首先调用"reset".注意普通的inputStreams不支持"reset",你可以调用它但不会发生任何事情.我的代码:

    public static Bitmap decodeSampledBitmapFromStream(InputStream inputStream,
                                                   int reqWidth, int reqHeight)
                             throws IOException {
    if (!widthHeightCheck(reqWidth, reqHeight)) 
        return BitmapFactory.decodeStream(inputStream);
    // First decode with inJustDecodeBounds=true to check dimensions
    if (!(inputStream instanceof BufferedInputStream)) {
        inputStream = new BufferedInputStream(inputStream);
    }
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    Rect rect = new Rect(-1, -1, -1, -1);
    BitmapFactory.decodeStream(inputStream, rect, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    inputStream.reset();
    return BitmapFactory.decodeStream(inputStream, rect, options);
}