Android ContentResolver.loadThumbnail转Kotlin

loadThumbnail原先是Java实现的，现在抠出来转Kotlin实现。

    private fun loadThumbnail(uri: Uri, size: Size, signal: CancellationSignal): Bitmap {
        return myLoadThumbnail(mContext?.contentResolver!!, uri, size, signal, ImageDecoder.ALLOCATOR_SOFTWARE)
    }

    private fun myLoadThumbnail(cr: ContentResolver, uri: Uri, size: Size, signal: CancellationSignal, allocator: Int): Bitmap {
        val opts = Bundle()
        opts.putParcelable(ContentResolver.EXTRA_SIZE, Point(size.width, size.height))
        val orientation = Int64Ref(0)

        var bitmap = ImageDecoder.decodeBitmap(ImageDecoder.createSource {
            val afd: AssetFileDescriptor = cr.openTypedAssetFile(
                uri, "image/*", opts,
                signal
            )!!
            val extras = afd.extras
            orientation.value = (extras?.getInt(DocumentsContract.EXTRA_ORIENTATION, 0) ?: 0).toLong()
            afd
        }) { decoder: ImageDecoder, info: ImageInfo, source: ImageDecoder.Source? ->
            decoder.allocator = allocator

            // One last-ditch check to see if we've been canceled.
            if (signal != null) signal.throwIfCanceled()

            // We requested a rough thumbnail size, but the remote size may have
            // returned something giant, so defensively scale down as needed.
            val widthSample = info.size.width / size.width
            val heightSample = info.size.height / size.height
            val sample = Math.max(widthSample, heightSample)
            if (sample > 1) {
                decoder.setTargetSampleSize(sample)
            }
        }

        // Transform the bitmap if requested. We use a side-channel to
        // communicate the orientation, since EXIF thumbnails don't contain
        // the rotation flags of the original image.

        // Transform the bitmap if requested. We use a side-channel to
        // communicate the orientation, since EXIF thumbnails don't contain
        // the rotation flags of the original image.
        if (orientation.value != 0L) {
            val width = bitmap.width
            val height = bitmap.height
            val m = Matrix()
            m.setRotate(orientation.value.toFloat(), (width / 2).toFloat(), (height / 2).toFloat())
            bitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, m, false)
        }

        return bitmap
    }

或者：

    private fun loadThumbnail(uri: Uri, size: Size, signal: CancellationSignal): Bitmap {
        return myLoadThumbnail(mContext?.contentResolver!!, uri, size, signal, ImageDecoder.ALLOCATOR_SOFTWARE)
    }

    private fun myLoadThumbnail(cr: ContentResolver, uri: Uri, size: Size, signal: CancellationSignal, allocator: Int): Bitmap {
        val opts = Bundle()
        opts.putParcelable(ContentResolver.EXTRA_SIZE, Point(size.width, size.height))
        val orientation = Int64Ref(0)

        val afd: AssetFileDescriptor = cr.openTypedAssetFile(
            uri, "image/*", opts,
            signal
        )!!

        val src = ImageDecoder.createSource {
            val extras = afd.extras
            orientation.value = (extras?.getInt(DocumentsContract.EXTRA_ORIENTATION, 0) ?: 0).toLong()
            afd
        }

        var bmp = ImageDecoder.decodeBitmap(src, ImageDecoder.OnHeaderDecodedListener { decoder, info, source ->
            decoder.allocator = allocator

            val widthSample = info.size.width / size.width
            val heightSample = info.size.height / size.height
            val sample = Math.max(widthSample, heightSample)
            if (sample > 1) {
                decoder.setTargetSampleSize(sample)
            }
        })

        if (orientation.value != 0L) {
            val width = bmp.width
            val height = bmp.height
            val m = Matrix()
            m.setRotate(orientation.value.toFloat(), (width / 2).toFloat(), (height / 2).toFloat())
            bmp = Bitmap.createBitmap(bmp, 0, 0, width, height, m, false)
        }

        return bmp
    }

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