Android ImageResizer（inSampleSize）

【Android ImageResizer（inSampleSize）】青春须早为，岂能长少年。这篇文章主要讲述Android ImageResizer：inSampleSize相关的知识，希望能为你提供帮助。

import android.annotation.TargetApi; import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Build; import com.example.android.common.logger.Log; import com.example.android.displayingbitmaps.BuildConfig; import java.io.FileDescriptor; /** * A simple subclass of {@link ImageWorker} that resizes images from resources given a target width * and height. Useful for when the input images might be too large to simply load directly into * memory. */ public class ImageResizer extends ImageWorker { private static final String TAG = "ImageResizer"; protected int mImageWidth; protected int mImageHeight; /** * Initialize providing a single target image size (used for both width and height); * * @param context * @param imageWidth * @param imageHeight */ public ImageResizer(Context context, int imageWidth, int imageHeight) { super(context); setImageSize(imageWidth, imageHeight); }/** * Initialize providing a single target image size (used for both width and height); * * @param context * @param imageSize */ public ImageResizer(Context context, int imageSize) { super(context); setImageSize(imageSize); }/** * Set the target image width and height. * * @param width * @param height */ public void setImageSize(int width, int height) { mImageWidth = width; mImageHeight = height; }/** * Set the target image size (width and height will be the same). * * @param size */ public void setImageSize(int size) { setImageSize(size, size); }/** * The main processing method. This happens in a background task. In this case we are just * sampling down the bitmap and returning it from a resource. * * @param resId * @return */ private Bitmap processBitmap(int resId) { if (BuildConfig.DEBUG) { Log.d(TAG, "processBitmap - " + resId); } return decodeSampledBitmapFromResource(mResources, resId, mImageWidth, mImageHeight, getImageCache()); }@Override protected Bitmap processBitmap(Object data) { return processBitmap(Integer.parseInt(String.valueOf(data))); }/** * Decode and sample down a bitmap from resources to the requested width and height. * * @param res The resources object containing the image data * @param resId The resource id of the image data * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @param cache The ImageCache used to find candidate bitmaps for use with inBitmap * @return A bitmap sampled down from the original with the same aspect ratio and dimensions *that are equal to or greater than the requested width and height */ public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight, ImageCache cache) {// BEGIN_INCLUDE (read_bitmap_dimensions) // First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeResource(res, resId, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // END_INCLUDE (read_bitmap_dimensions)// If we\'re running on Honeycomb or newer, try to use inBitmap if (Utils.hasHoneycomb()) { addInBitmapOptions(options, cache); }// Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; return BitmapFactory.decodeResource(res, resId, options); }/** * Decode and sample down a bitmap from a file to the requested width and height. * * @param filename The full path of the file to decode * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @param cache The ImageCache used to find candidate bitmaps for use with inBitmap * @return A bitmap sampled down from the original with the same aspect ratio and dimensions *that are equal to or greater than the requested width and height */ public static Bitmap decodeSampledBitmapFromFile(String filename, int reqWidth, int reqHeight, ImageCache cache) {// First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFile(filename, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // If we\'re running on Honeycomb or newer, try to use inBitmap if (Utils.hasHoneycomb()) { addInBitmapOptions(options, cache); }// Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; return BitmapFactory.decodeFile(filename, options); }/** * Decode and sample down a bitmap from a file input stream to the requested width and height. * * @param fileDescriptor The file descriptor to read from * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @param cache The ImageCache used to find candidate bitmaps for use with inBitmap * @return A bitmap sampled down from the original with the same aspect ratio and dimensions *that are equal to or greater than the requested width and height */ public static Bitmap decodeSampledBitmapFromDescriptor( FileDescriptor fileDescriptor, int reqWidth, int reqHeight, ImageCache cache) {// First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; // If we\'re running on Honeycomb or newer, try to use inBitmap if (Utils.hasHoneycomb()) { addInBitmapOptions(options, cache); }return BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); }@TargetApi(Build.VERSION_CODES.HONEYCOMB) private static void addInBitmapOptions(BitmapFactory.Options options, ImageCache cache) {// inBitmap only works with mutable bitmaps so force the decoder to // return mutable bitmaps. options.inMutable = true; if (cache != null) { // Try and find a bitmap to use for inBitmap Bitmap inBitmap = cache.getBitmapFromReusableSet(options); if (inBitmap != null) { options.inBitmap = inBitmap; } }}/** * Calculate an inSampleSize for use in a {@link android.graphics.BitmapFactory.Options} object when decoding * bitmaps using the decode* methods from {@link android.graphics.BitmapFactory}. This implementation calculates * the closest inSampleSize that is a power of 2 and will result in the final decoded bitmap * having a width and height equal to or larger than the requested width and height. * * @param options An options object with out* params already populated (run through a decode* *method with inJustDecodeBounds==true * @param reqWidth The requested width of the resulting bitmap * @param reqHeight The requested height of the resulting bitmap * @return The value to be used for inSampleSize */ public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { // BEGIN_INCLUDE (calculate_sample_size) // 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; }// This offers some additional logic in case the image has a strange // aspect ratio. For example, a panorama may have a much larger // width than height. In these cases the total pixels might still // end up being too large to fit comfortably in memory, so we should // be more aggressive with sample down the image (=larger inSampleSize).long totalPixels = width * height / inSampleSize; // Anything more than 2x the requested pixels we\'ll sample down further final long totalReqPixelsCap = reqWidth * reqHeight * 2; while (totalPixels > totalReqPixelsCap) { inSampleSize *= 2; totalPixels /= 2; } } return inSampleSize; // END_INCLUDE (calculate_sample_size) } }

DisplayingBitmaps.rar