BitmapFactory.decode设置选项时流返回空值

image android java bitmap

2022-08-31 10:52:20

我遇到了问题。在没有选项的情况下使用它时，它将返回图像。但是当我将它与选项一起使用时，它永远不会返回位图。BitmapFactory.decodeStream(inputStream).decodeStream(inputStream, null, options)

我试图做的是在实际加载位图之前对其进行缩减采样以节省内存。我读过一些很好的指南，但没有一个使用..decodeStream

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);

答案 1

问题在于，一旦您使用来自 HttpUrlConnection 的 InputStream 来获取图像元数据，就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新的输入流。

  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();

答案 2

尝试使用 BufferedInputStream 包装 InputStream。

InputStream is = new BufferedInputStream(conn.getInputStream());
is.mark(is.available());
// Do the bound decoding
// inJustDecodeBounds =true
is.reset();  
// Do the actual decoding