设置选项时 BitmapFactory.decodeStream 返回 null [英] BitmapFactory.decodeStream returning null when options are set

问题描述

我在使用 BitmapFactory.decodeStream(inputStream) 时遇到问题.在没有选项的情况下使用它时，它将返回一个图像.但是当我将它与 .decodeStream(inputStream, null, options) 中的选项一起使用时，它永远不会返回位图.

I'm having issues with BitmapFactory.decodeStream(inputStream). When using it without options, it will return an image. But when I use it with options as in .decodeStream(inputStream, null, options) it never returns Bitmaps.

我想做的是在实际加载位图之前对其进行下采样以节省内存.我读过一些很好的指南，但没有使用 .decodeStream.

What I'm trying to do is to downsample a Bitmap before I actually load it to save memory. I've read some good guides, but none using .decodeStream.

• 处理大型位图

这里

Android 中的图像处理

工作正常

URL url = new URL(sUrl);
HttpURLConnection connection  = (HttpURLConnection) url.openConnection();

InputStream is = connection.getInputStream();
Bitmap img = BitmapFactory.decodeStream(is, null, options);

不起作用

InputStream is = connection.getInputStream();
Bitmap img = BitmapFactory.decodeStream(is, null, options);

InputStream is = connection.getInputStream();

Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;

BitmapFactory.decodeStream(is, null, options);

Boolean scaleByHeight = Math.abs(options.outHeight - TARGET_HEIGHT) >= Math.abs(options.outWidth - TARGET_WIDTH);

if (options.outHeight * options.outWidth * 2 >= 200*100*2){
    // Load, scaling to smallest power of 2 that'll get it <= desired dimensions
    double sampleSize = scaleByHeight
    ? options.outHeight / TARGET_HEIGHT
    : options.outWidth / TARGET_WIDTH;
    options.inSampleSize =
        (int)Math.pow(2d, Math.floor(
        Math.log(sampleSize)/Math.log(2d)));
}

// Do the actual decoding
options.inJustDecodeBounds = false;
Bitmap img = BitmapFactory.decodeStream(is, null, options);

推荐答案

问题在于，一旦您使用了来自 HttpUrlConnection 的 InputStream 来获取图像元数据，就无法回退并再次使用相同的 InputStream.

The problem was that once you've used an InputStream from a HttpUrlConnection to fetch image metadata, you can't rewind and use the same InputStream again.

>

因此您必须为图像的实际采样创建一个新的 InputStream.

Therefore you have to create a new InputStream for the actual sampling of the image.

  Options options = new BitmapFactory.Options();
  options.inJustDecodeBounds = true;

  BitmapFactory.decodeStream(is, null, options);

  Boolean scaleByHeight = Math.abs(options.outHeight - TARGET_HEIGHT) >= Math.abs(options.outWidth - TARGET_WIDTH);

  if(options.outHeight * options.outWidth * 2 >= 200*200*2){
         // Load, scaling to smallest power of 2 that'll get it <= desired dimensions
        double sampleSize = scaleByHeight
              ? options.outHeight / TARGET_HEIGHT
              : options.outWidth / TARGET_WIDTH;
        options.inSampleSize = 
              (int)Math.pow(2d, Math.floor(
              Math.log(sampleSize)/Math.log(2d)));
     }

        // Do the actual decoding
        options.inJustDecodeBounds = false;

        is.close();
        is = getHTTPConnectionInputStream(sUrl);
        Bitmap img = BitmapFactory.decodeStream(is, null, options);
        is.close();

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