尝试缩放 android 图库中的图像和 return 位图

Question

我目前正在从 android 图库中提取图像，其中 returns 一个 uri 到 activity 进行预览，然后被发送到 Parse 数据库。

发送的图片太大所以我实现了方法found in the android developer documentation

这是我正在使用的东西

Uri selectedImage = data.getData();
            InputStream imageStream = getContentResolver().openInputStream(selectedImage);

            imageBitmap = getBitmapFromReturnedImage(imageStream, 800, 800);

//                ByteArrayOutputStream stream = new ByteArrayOutputStream();
// LINE 2                imageBitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
//                byte[] byteArray = stream.toByteArray();
//
//                parseFile = new ParseFile("location_image.jpg", byteArray);

            mImage.setImageBitmap(imageBitmap);



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) {

        final int halfHeight = height / 2;
        final int halfWidth = width / 2;

        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while ((halfHeight / inSampleSize) > reqHeight
                && (halfWidth / inSampleSize) > reqWidth) {
            inSampleSize *= 2;
        }
    }

    return inSampleSize;
}

public static Bitmap getBitmapFromReturnedImage(InputStream inputStream, int reqWidth, int reqHeight) {

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

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

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

注释"LINE 2"，当该部分未被注释时，returns 一个空指针异常，这让我大吃一惊。对该部分进行评论后，当我运行该应用程序时，图像视图看起来只是空的。

有什么线索吗？

Answer 1

在第二次调用decodeStream 之前，您需要在读取边界后返回到InputStream 的开头，否则您将得到无效的Bitmap。最简单的方法就是关闭流并再次打开它。

试试这个代码（注意函数不再是静态的，允许调用 getContentResolver() 并且你传入的是 Uri 而不是 InputStream）：

public Bitmap getBitmapFromReturnedImage(Uri selectedImage, int reqWidth, int reqHeight) throws IOException {

    InputStream inputStream = getContentResolver().openInputStream(selectedImage);

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

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

    // close the input stream
    inputStream.close();

    // reopen the input stream
    inputStream = getContentResolver().openInputStream(selectedImage);      

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

像这样打电话

Uri selectedImage = data.getData();
imageBitmap = getBitmapFromReturnedImage(selectedImage, 800, 800);

尝试缩放 android 图库中的图像和 return 位图

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