編輯:Android開發實例
Android 2.2開始新增的縮略圖類ThumbnailUtils的主要方法是靜態的,對於Android 2.2或API Level8以下的工程可以直接使用,本類相對於我們常規的縮略圖類考慮更周全,除了尺寸比例優化外,針對OOM的內存管理方面有更周全的處理方式,完整代碼如下,使用方法和介紹請查看 ThumbnailUtils - Android2.2新增類 一文
- public class ThumbnailUtils {
- private static final String TAG = "ThumbnailUtils";
- /* Maximum pixels size for created bitmap. */
- private static final int MAX_NUM_PIXELS_THUMBNAIL = 512 * 384;
- private static final int MAX_NUM_PIXELS_MICRO_THUMBNAIL = 128 * 128;
- private static final int UNCONSTRAINED = -1;
- /* Options used internally. */
- private static final int OPTIONS_NONE = 0x0;
- private static final int OPTIONS_SCALE_UP = 0x1;
- /**
- * Constant used to indicate we should recycle the input in
- * [email protected] #extractThumbnail(Bitmap, int, int, int)} unless the output is the input.
- */
- public static final int OPTIONS_RECYCLE_INPUT = 0x2;
- /**
- * Constant used to indicate the dimension of mini thumbnail.
- * @hide Only used by media framework and media provider internally.
- */
- public static final int TARGET_SIZE_MINI_THUMBNAIL = 320;
- /**
- * Constant used to indicate the dimension of micro thumbnail.
- * @hide Only used by media framework and media provider internally.
- */
- public static final int TARGET_SIZE_MICRO_THUMBNAIL = 96;
- /**
- * This method first examines if the thumbnail embedded in EXIF is bigger than our target
- * size. If not, then it'll create a thumbnail from original image. Due to efficiency
- * consideration, we want to let MediaThumbRequest avoid calling this method twice for
- * both kinds, so it only requests for MICRO_KIND and set saveImage to true.
- *
- * This method always returns a "square thumbnail" for MICRO_KIND thumbnail.
- *
- * @param filePath the path of image file
- * @param kind could be MINI_KIND or MICRO_KIND
- * @return Bitmap
- *
- * @hide This method is only used by media framework and media provider internally.
- */
- public static Bitmap createImageThumbnail(String filePath, int kind) {
- boolean wantMini = (kind == Images.Thumbnails.MINI_KIND);
- int targetSize = wantMini
- ? TARGET_SIZE_MINI_THUMBNAIL
- : TARGET_SIZE_MICRO_THUMBNAIL;
- int maxPixels = wantMini
- ? MAX_NUM_PIXELS_THUMBNAIL
- : MAX_NUM_PIXELS_MICRO_THUMBNAIL;
- SizedThumbnailBitmap sizedThumbnailBitmap = new SizedThumbnailBitmap();
- Bitmap bitmap = null;
- MediaFileType fileType = MediaFile.getFileType(filePath);
- if (fileType != null && fileType.fileType == MediaFile.FILE_TYPE_JPEG) {
- createThumbnailFromEXIF(filePath, targetSize, maxPixels, sizedThumbnailBitmap);
- bitmap = sizedThumbnailBitmap.mBitmap;
- }
- if (bitmap == null) {
- try {
- FileDescriptor fd = new FileInputStream(filePath).getFD();
- BitmapFactory.Options options = new BitmapFactory.Options();
- options.inSampleSize = 1;
- options.inJustDecodeBounds = true;
- BitmapFactory.decodeFileDescriptor(fd, null, options);
- if (options.mCancel || options.outWidth == -1
- || options.outHeight == -1) {
- return null;
- }
- options.inSampleSize = computeSampleSize(
- options, targetSize, maxPixels);
- options.inJustDecodeBounds = false;
- options.inDither = false;
- options.inPreferredConfig = Bitmap.Config.ARGB_8888;
- bitmap = BitmapFactory.decodeFileDescriptor(fd, null, options);
- } catch (IOException ex) {
- Log.e(TAG, "", ex);
- }
- }
- if (kind == Images.Thumbnails.MICRO_KIND) {
- // now we make it a "square thumbnail" for MICRO_KIND thumbnail
- bitmap = extractThumbnail(bitmap,
- TARGET_SIZE_MICRO_THUMBNAIL,
- TARGET_SIZE_MICRO_THUMBNAIL, OPTIONS_RECYCLE_INPUT);
- }
- return bitmap;
- }
- /**
- * Create a video thumbnail for a video. May return null if the video is
- * corrupt or the format is not supported.
- *
- * @param filePath the path of video file
- * @param kind could be MINI_KIND or MICRO_KIND
- */
- public static Bitmap createVideoThumbnail(String filePath, int kind) {
- Bitmap bitmap = null;
- MediaMetadataRetriever retriever = new MediaMetadataRetriever();
- try {
- retriever.setMode(MediaMetadataRetriever.MODE_CAPTURE_FRAME_ONLY);
- retriever.setDataSource(filePath);
- bitmap = retriever.captureFrame();
- } catch (IllegalArgumentException ex) {
- // Assume this is a corrupt video file
- } catch (RuntimeException ex) {
- // Assume this is a corrupt video file.
- } finally {
- try {
- retriever.release();
- } catch (RuntimeException ex) {
- // Ignore failures while cleaning up.
- }
- }
- if (kind == Images.Thumbnails.MICRO_KIND && bitmap != null) {
- bitmap = extractThumbnail(bitmap,
- TARGET_SIZE_MICRO_THUMBNAIL,
- TARGET_SIZE_MICRO_THUMBNAIL,
- OPTIONS_RECYCLE_INPUT);
- }
- return bitmap;
- }
- /**
- * Creates a centered bitmap of the desired size.
- *
- * @param source original bitmap source
- * @param width targeted width
- * @param height targeted height
- */
- public static Bitmap extractThumbnail(
- Bitmap source, int width, int height) {
- return extractThumbnail(source, width, height, OPTIONS_NONE);
- }
- /**
- * Creates a centered bitmap of the desired size.
- *
- * @param source original bitmap source
- * @param width targeted width
- * @param height targeted height
- * @param options options used during thumbnail extraction
- */
- public static Bitmap extractThumbnail(
- Bitmap source, int width, int height, int options) {
- if (source == null) {
- return null;
- }
- float scale;
- if (source.getWidth() < source.getHeight()) {
- scale = width / (float) source.getWidth();
- } else {
- scale = height / (float) source.getHeight();
- }
- Matrix matrix = new Matrix();
- matrix.setScale(scale, scale);
- Bitmap thumbnail = transform(matrix, source, width, height,
- OPTIONS_SCALE_UP | options);
- return thumbnail;
- }
- /*
- * Compute the sample size as a function of minSideLength
- * and maxNumOfPixels.
- * minSideLength is used to specify that minimal width or height of a
- * bitmap.
- * maxNumOfPixels is used to specify the maximal size in pixels that is
- * tolerable in terms of memory usage.
- *
- * The function returns a sample size based on the constraints.
- * Both size and minSideLength can be passed in as IImage.UNCONSTRAINED,
- * which indicates no care of the corresponding constraint.
- * The functions prefers returning a sample size that
- * generates a smaller bitmap, unless minSideLength = IImage.UNCONSTRAINED.
- *
- * Also, the function rounds up the sample size to a power of 2 or multiple
- * of 8 because BitmapFactory only honors sample size this way.
- * For example, BitmapFactory downsamples an image by 2 even though the
- * request is 3. So we round up the sample size to avoid OOM.
- */
- private static int computeSampleSize(BitmapFactory.Options options,
- int minSideLength, int maxNumOfPixels) {
- int initialSize = computeInitialSampleSize(options, minSideLength,
- maxNumOfPixels);
- int roundedSize;
- if (initialSize <= 8 ) {
- roundedSize = 1;
- while (roundedSize < initialSize) {
- roundedSize <<= 1;
- }
- } else {
- roundedSize = (initialSize + 7) / 8 * 8;
- }
- return roundedSize;
- }
- private static int computeInitialSampleSize(BitmapFactory.Options options,
- int minSideLength, int maxNumOfPixels) {
- double w = options.outWidth;
- double h = options.outHeight;
- int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 :
- (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
- int upperBound = (minSideLength == UNCONSTRAINED) ? 128 :
- (int) Math.min(Math.floor(w / minSideLength),
- Math.floor(h / minSideLength));
- if (upperBound < lowerBound) {
- // return the larger one when there is no overlapping zone.
- return lowerBound;
- }
- if ((maxNumOfPixels == UNCONSTRAINED) &&
- (minSideLength == UNCONSTRAINED)) {
- return 1;
- } else if (minSideLength == UNCONSTRAINED) {
- return lowerBound;
- } else {
- return upperBound;
- }
- }
- /**
- * Make a bitmap from a given Uri, minimal side length, and maximum number of pixels.
- * The image data will be read from specified pfd if it's not null, otherwise
- * a new input stream will be created using specified ContentResolver.
- *
- * Clients are allowed to pass their own BitmapFactory.Options used for bitmap decoding. A
- * new BitmapFactory.Options will be created if options is null.
- */
- private static Bitmap makeBitmap(int minSideLength, int maxNumOfPixels,
- Uri uri, ContentResolver cr, ParcelFileDescriptor pfd,
- BitmapFactory.Options options) {
- Bitmap b = null;
- try {
- if (pfd == null) pfd = makeInputStream(uri, cr);
- if (pfd == null) return null;
- if (options == null) options = new BitmapFactory.Options();
- FileDescriptor fd = pfd.getFileDescriptor();
- options.inSampleSize = 1;
- options.inJustDecodeBounds = true;
- BitmapFactory.decodeFileDescriptor(fd, null, options);
- if (options.mCancel || options.outWidth == -1
- || options.outHeight == -1) {
- return null;
- }
- options.inSampleSize = computeSampleSize(
- options, minSideLength, maxNumOfPixels);
- options.inJustDecodeBounds = false;
- options.inDither = false;
- options.inPreferredConfig = Bitmap.Config.ARGB_8888;
- b = BitmapFactory.decodeFileDescriptor(fd, null, options);
- } catch (OutOfMemoryError ex) {
- Log.e(TAG, "Got oom exception ", ex);
- return null;
- } finally {
- closeSilently(pfd);
- }
- return b;
- }
- private static void closeSilently(ParcelFileDescriptor c) {
- if (c == null) return;
- try {
- c.close();
- } catch (Throwable t) {
- // do nothing
- }
- }
- private static ParcelFileDescriptor makeInputStream(
- Uri uri, ContentResolver cr) {
- try {
- return cr.openFileDescriptor(uri, "r");
- } catch (IOException ex) {
- return null;
- }
- }
- /**
- * Transform source Bitmap to targeted width and height.
- */
- private static Bitmap transform(Matrix scaler,
- Bitmap source,
- int targetWidth,
- int targetHeight,
- int options) {
- boolean scaleUp = (options & OPTIONS_SCALE_UP) != 0;
- boolean recycle = (options & OPTIONS_RECYCLE_INPUT) != 0;
- int deltaX = source.getWidth() - targetWidth;
- int deltaY = source.getHeight() - targetHeight;
- if (!scaleUp && (deltaX < 0 || deltaY < 0)) {
- /*
- * In this case the bitmap is smaller, at least in one dimension,
- * than the target. Transform it by placing as much of the image
- * as possible into the target and leaving the top/bottom or
- * left/right (or both) black.
- */
- Bitmap b2 = Bitmap.createBitmap(targetWidth, targetHeight,
- Bitmap.Config.ARGB_8888);
- Canvas c = new Canvas(b2);
- int deltaXHalf = Math.max(0, deltaX / 2);
- int deltaYHalf = Math.max(0, deltaY / 2);
- Rect src = new Rect(
- deltaXHalf,
- deltaYHalf,
- deltaXHalf + Math.min(targetWidth, source.getWidth()),
- deltaYHalf + Math.min(targetHeight, source.getHeight()));
- int dstX = (targetWidth - src.width()) / 2;
- int dstY = (targetHeight - src.height()) / 2;
- Rect dst = new Rect(
- dstX,
- dstY,
- targetWidth - dstX,
- targetHeight - dstY);
- c.drawBitmap(source, src, dst, null);
- if (recycle) {
- source.recycle();
- }
- return b2;
- }
- float bitmapWidthF = source.getWidth();
- float bitmapHeightF = source.getHeight();
- float bitmapAspect = bitmapWidthF / bitmapHeightF;
- float viewAspect = (float) targetWidth / targetHeight;
- if (bitmapAspect > viewAspect) {
- float scale = targetHeight / bitmapHeightF;
- if (scale < .9F || scale > 1F) {
- scaler.setScale(scale, scale);
- } else {
- scaler = null;
- }
- } else {
- float scale = targetWidth / bitmapWidthF;
- if (scale < .9F || scale > 1F) {
- scaler.setScale(scale, scale);
- } else {
- scaler = null;
- }
- }
- Bitmap b1;
- if (scaler != null) {
- // this is used for minithumb and crop, so we want to filter here.
- b1 = Bitmap.createBitmap(source, 0, 0,
- source.getWidth(), source.getHeight(), scaler, true);
- } else {
- b1 = source;
- }
- if (recycle && b1 != source) {
- source.recycle();
- }
- int dx1 = Math.max(0, b1.getWidth() - targetWidth);
- int dy1 = Math.max(0, b1.getHeight() - targetHeight);
- Bitmap b2 = Bitmap.createBitmap(
- b1,
- dx1 / 2,
- dy1 / 2,
- targetWidth,
- targetHeight);
- if (b2 != b1) {
- if (recycle || b1 != source) {
- b1.recycle();
- }
- }
- return b2;
- }
- /**
- * SizedThumbnailBitmap contains the bitmap, which is downsampled either from
- * the thumbnail in exif or the full image.
- * mThumbnailData, mThumbnailWidth and mThumbnailHeight are set together only if mThumbnail
- * is not null.
- *
- * The width/height of the sized bitmap may be different from mThumbnailWidth/mThumbnailHeight.
- */
- private static class SizedThumbnailBitmap {
- public byte[] mThumbnailData;
- public Bitmap mBitmap;
- public int mThumbnailWidth;
- public int mThumbnailHeight;
- }
- /**
- * Creates a bitmap by either downsampling from the thumbnail in EXIF or the full image.
- * The functions returns a SizedThumbnailBitmap,
- * which contains a downsampled bitmap and the thumbnail data in EXIF if exists.
- */
- private static void createThumbnailFromEXIF(String filePath, int targetSize,
- int maxPixels, SizedThumbnailBitmap sizedThumbBitmap) {
- if (filePath == null) return;
- ExifInterface exif = null;
- byte [] thumbData = null;
- try {
- exif = new ExifInterface(filePath);
- if (exif != null) {
- thumbData = exif.getThumbnail();
- }
- } catch (IOException ex) {
- Log.w(TAG, ex);
- }
- BitmapFactory.Options fullOptions = new BitmapFactory.Options();
- BitmapFactory.Options exifOptions = new BitmapFactory.Options();
- int exifThumbWidth = 0;
- int fullThumbWidth = 0;
- // Compute exifThumbWidth.
- if (thumbData != null) {
- exifOptions.inJustDecodeBounds = true;
- BitmapFactory.decodeByteArray(thumbData, 0, thumbData.length, exifOptions);
- exifOptions.inSampleSize = computeSampleSize(exifOptions, targetSize, maxPixels);
- exifThumbWidth = exifOptions.outWidth / exifOptions.inSampleSize;
- }
- // Compute fullThumbWidth.
- fullOptions.inJustDecodeBounds = true;
- BitmapFactory.decodeFile(filePath, fullOptions);
- fullOptions.inSampleSize = computeSampleSize(fullOptions, targetSize, maxPixels);
- fullThumbWidth = fullOptions.outWidth / fullOptions.inSampleSize;
- // Choose the larger thumbnail as the returning sizedThumbBitmap.
- if (thumbData != null && exifThumbWidth >= fullThumbWidth) {
- int width = exifOptions.outWidth;
- int height = exifOptions.outHeight;
- exifOptions.inJustDecodeBounds = false;
- sizedThumbBitmap.mBitmap = BitmapFactory.decodeByteArray(thumbData, 0,
- thumbData.length, exifOptions);
- if (sizedThumbBitmap.mBitmap != null) {
- sizedThumbBitmap.mThumbnailData = thumbData;
- sizedThumbBitmap.mThumbnailWidth = width;
- sizedThumbBitmap.mThumbnailHeight = height;
- }
- } else {
- fullOptions.inJustDecodeBounds = false;
- sizedThumbBitmap.mBitmap = BitmapFactory.decodeFile(filePath, fullOptions);
- }
- }
- }
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