decodeStream 返回 null [英] decodeStream returns null

问题描述

我正在尝试采用 位图调整大小 教程 -唯一的区别是我使用 decodeStream 而不是 decodeResource.这很奇怪，但是没有任何操作的 decodeStream 给了我一个位图 obj，但是当我通过 decodeSampledBitmapFromStream 时它由于某种原因返回 null.我该如何解决?

I'm trying to adopt bitmap resizing tutorial - the only difference is that I use decodeStream instead of decodeResource. It's strange but decodeStream, without any manipulations, gives me a bitmap obj, but when I go through decodeSampledBitmapFromStream it returns null for some reason. How do I fix it ?

这是我使用的代码:

protected Handler _onPromoBlocksLoad = new Handler() {
        @Override
        public void dispatchMessage(Message msg) {
            PromoBlocksContainer c = (PromoBlocksContainer) _promoBlocksFactory.getResponse();
            HttpRequest request = new HttpRequest(c.getPromoBlocks().get(0).getSmallThumbnail());

            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = true;
            InputStream stream;
            ImageView v = (ImageView) findViewById(R.id.banner);
            try {
                stream = request.getStream();

                //v.setImageBitmap(BitmapFactory.decodeStream(stream)); Works fine
                Bitmap img = decodeSampledBitmapFromStream(stream, v.getWidth(), v.getHeight());
                v.setImageBitmap(img);
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        }
    };

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

    public static Bitmap decodeSampledBitmapFromStream(InputStream res, int reqWidth, int reqHeight) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(res, null, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        Bitmap img =  BitmapFactory.decodeStream(res, null, options); // Gives  null 
        return img;
    }

推荐答案

问题是，一旦您使用了来自 HttpUrlConnection 的 InputStream，您将无法倒带并再次使用相同的 InputStream.因此，您必须为图像的实际采样创建一个新的 InputStream.否则我们必须中止 http 请求.

The problem was that once you've used an InputStream from a HttpUrlConnection, you can't rewind and use the same InputStream again. Therefore you have to create a new InputStream for the actual sampling of the image. Otherwise we have to abort the http request.

request.abort();

这篇关于decodeStream 返回 null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！