android - 无法使用 BitmapFactory.decodeStream() 从 Url 加载图像

Question

我正在尝试从 URL 下载图像以显示为 ImageView。下载是在后台使用 AsyncTask 完成的。但是，对 BitmapFactory 的 decodeStream 的调用总是返回一个空对象。我验证了为连接提供的 Url 是正确的，但似乎 BitmapFactory 无法从 HTTP 连接返回的 InputStream 中读取图像。这是下面的代码:

@Override
    protected Bitmap doInBackground(String... uri) {
        Bitmap bm = null;
        HttpClient client = new DefaultHttpClient();
        HttpGet request = new HttpGet(Uri.encode(uri[0]));
        try {
            HttpResponse response = client.execute(request);
            HttpEntity entity = response.getEntity();
            String contentType = entity.getContentType().getValue();
            DisplayMetrics metrics = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(metrics);
            int halfScreen = metrics.widthPixels / 2;
            int photoWidth = halfScreen > 200 ? 200 : halfScreen;
            if (contentType.contains("image/jpeg") || contentType.contains("image/png") || contentType.contains("image/gif")) {
                bm = BitmapFactory.decodeStream(new BufferedInputStream(entity.getContent()));
                if (bm.getWidth() > photoWidth)
                bm = Bitmap.createScaledBitmap(bm, photoWidth, Math.round((photoWidth*bm.getHeight())/bm.getWidth()), true);
            }
        } catch (Exception e) {
            bm = null;
        }
        return bm;
    }

奇怪的是，完全相同的代码在 Nexus S 上运行良好，但在运行 Android 2.1-update1 的三星上却不起作用。

Answer 1

问题出在 BitmapFactory.decodeStream() 方法中。似乎此方法有一个错误，导致它在慢速连接时失败。我应用了在 http://code.google.com/p/android/issues/detail?id=6066 找到的建议.

我在下面创建了 FlushedInputStream 类:

public class FlushedInputStream extends FilterInputStream {

protected FlushedInputStream(InputStream in) {
    super(in);
}

@Override
public long skip(long n) throws IOException {
    long totalBytesSkipped = 0L;
    while (totalBytesSkipped < n) {
        long bytesSkipped = in.skip(n - totalBytesSkipped);
        if (bytesSkipped == 0L) {
              int onebyte = read();
              if (onebyte < 0) {
                  break;  // we reached EOF
              } else {
                  bytesSkipped = 1; // we read one byte
              }
       }
        totalBytesSkipped += bytesSkipped;
    }
    return totalBytesSkipped;
}
}

然后，在我的代码中我使用了:

bm = BitmapFactory.decodeStream(new FlushedInputStream(entity.getContent()));

代替:

bm = BitmapFactory.decodeStream(new BufferedInputStream(entity.getContent()));