Creates Bitmap objects from various sources, including files, streams,and byte-arrays.

 /** * Synonym for opening the given resource and calling * {@link #decodeResourceStream}. * * @param res The resources object containing the image data * @param id The resource id of the image data * @param opts null-ok; Options that control downsampling and whether the *  image should be completely decoded, or just is size returned. * @return The decoded bitmap, or null if the image data could not be *  decoded, or, if opts is non-null, if opts requested only the *  size be returned (in opts.outWidth and opts.outHeight) * @throws IllegalArgumentException if {@link BitmapFactory.Options#inPreferredConfig} *  is {@link android.graphics.Bitmap.Config#HARDWARE} *  and {@link BitmapFactory.Options#inMutable} is set, if the specified color space *  is not {@link ColorSpace.Model#RGB RGB}, or if the specified color space's transfer *  function is not an {@link ColorSpace.Rgb.TransferParameters ICC parametric curve} */ public static Bitmap decodeResource(Resources res, int id, Options opts) {

 /** * If set to true, the decoder will return null (no bitmap), but * the <code>out...</code> fields will still be set, allowing the caller to * query the bitmap without having to allocate the memory for its pixels. */ public boolean inJustDecodeBounds;

 BitmapFactory.Options options = new BitmapFactory.Options(); // 指定在解析圖片文件時，僅僅解析邊緣信息而不創(chuàng)建 bitmap 對象。 options.inJustDecodeBounds = true; // R.drawable.test 是使用的 2560x1920 的測試圖片資源文件。 BitmapFactory.decodeResource(getResources(), R.drawable.test, options); int width = options.outWidth; int height = options.outHeight; Log.i(TAG, "width: " + width + ", height: " + height);

 /** * If set to a value > 1, requests the decoder to subsample the original * image, returning a smaller image to save memory. The sample size is * the number of pixels in either dimension that correspond to a single * pixel in the decoded bitmap. For example, inSampleSize == 4 returns * an image that is 1/4 the width/height of the original, and 1/16 the * number of pixels. Any value <= 1 is treated the same as 1. Note: the * decoder uses a final value based on powers of 2, any other value will * be rounded down to the nearest power of 2. */ public int inSampleSize;

 /** * @param originWidth the width of the origin bitmap * @param originHeight the height of the origin bitmap * @param desWidth the max width of the desired bitmap * @param desHeight the max height of the desired bitmap * @return the optimal sample size to make sure the size of bitmap is not more than the desired. */ public static int calculateSampleSize(int originWidth, int originHeight, int desWidth, int desHeight) { int sampleSize = 1; int width = originWidth; int height = originHeight; while((width / sampleSize) > desWidth && (height / sampleSize) > desHeight) {  sampleSize *= 2; } return sampleSize; }

 int sampleSize = BitmapCompressor.calculateSampleSize(2560, 1920, 100, 100); Log.i(TAG, "sampleSize: " + sampleSize);

 public static Bitmap compressBitmapResource(Resources res, int resId, int inSampleSize) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = false; options.inSampleSize = inSampleSize; return BitmapFactory.decodeResource(res, resId, options); }

 /** * BitmapRegionDecoder can be used to decode a rectangle region from an image. * BitmapRegionDecoder is particularly useful when an original image is large and * you only need parts of the image. * * <p>To create a BitmapRegionDecoder, call newInstance(...). * Given a BitmapRegionDecoder, users can call decodeRegion() repeatedly * to get a decoded Bitmap of the specified region. * */ public final class BitmapRegionDecoder { ... }

 /** * Create a BitmapRegionDecoder from an input stream. * The stream's position will be where ever it was after the encoded data * was read. * Currently only the JPEG and PNG formats are supported. * * @param is The input stream that holds the raw data to be decoded into a *  BitmapRegionDecoder. * @param isShareable If this is true, then the BitmapRegionDecoder may keep a *   shallow reference to the input. If this is false, *   then the BitmapRegionDecoder will explicitly make a copy of the *   input data, and keep that. Even if sharing is allowed, *   the implementation may still decide to make a deep *   copy of the input data. If an image is progressively encoded, *   allowing sharing may degrade the decoding speed. * @return BitmapRegionDecoder, or null if the image data could not be decoded. * @throws IOException if the image format is not supported or can not be decoded. * * <p class="note">Prior to {@link android.os.Build.VERSION_CODES#KITKAT}, * if {@link InputStream#markSupported is.markSupported()} returns true, * <code>is.mark(1024)</code> would be called. As of * {@link android.os.Build.VERSION_CODES#KITKAT}, this is no longer the case.</p> */ public static BitmapRegionDecoder newInstance(InputStream is,  boolean isShareable) throws IOException { ... }

 /** * Decodes a rectangle region in the image specified by rect. * * @param rect The rectangle that specified the region to be decode. * @param options null-ok; Options that control downsampling. *  inPurgeable is not supported. * @return The decoded bitmap, or null if the image data could not be *  decoded. * @throws IllegalArgumentException if {@link BitmapFactory.Options#inPreferredConfig} *  is {@link android.graphics.Bitmap.Config#HARDWARE} *  and {@link BitmapFactory.Options#inMutable} is set, if the specified color space *  is not {@link ColorSpace.Model#RGB RGB}, or if the specified color space's transfer *  function is not an {@link ColorSpace.Rgb.TransferParameters ICC parametric curve} */ public Bitmap decodeRegion(Rect rect, BitmapFactory.Options options) { ... }

 // 解析得到原圖的長寬值，方便后面進(jìn)行局部顯示時指定需要顯示的區(qū)域。 BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeResource(getResources(), R.drawable.test, options); int width = options.outWidth; int height = options.outHeight; try { // 創(chuàng)建局部解析器  InputStream inputStream = getResources().openRawResource(R.drawable.test); BitmapRegionDecoder decoder = BitmapRegionDecoder.newInstance(inputStream,false);  // 指定需要顯示的矩形區(qū)域，這里要顯示的原圖的左上 1/4 區(qū)域。 Rect rect = new Rect(0, 0, width / 2, height / 2); // 創(chuàng)建位圖配置，這里使用 RGB_565，每個像素占 2 字節(jié)。 BitmapFactory.Options regionOptions = new BitmapFactory.Options(); regionOptions.inPreferredConfig = Bitmap.Config.RGB_565;  // 創(chuàng)建得到指定區(qū)域的 Bitmap 對象并進(jìn)行顯示。 Bitmap regionBitmap = decoder.decodeRegion(rect,regionOptions); ImageView imageView = (ImageView) findViewById(R.id.main_image); imageView.setImageBitmap(regionBitmap); } catch (Exception e) { e.printStackTrace(); }

/** * A cache that holds strong references to a limited number of values. Each time * a value is accessed, it is moved to the head of a queue. When a value is * added to a full cache, the value at the end of that queue is evicted and may * become eligible for garbage collection. */public class LruCache<K, V> { ... }

 // 獲得進(jìn)程可以使用的最大內(nèi)存量 int maxMemory = (int) Runtime.getRuntime().maxMemory();  mCache = new LruCache<String, Bitmap>(maxMemory / 4) {  @Override  protected int sizeOf(String key, Bitmap value) {   return value.getByteCount();  } };

 public Bitmap get(String key) {  Bitmap bitmap = mCache.get(key);  if (bitmap != null) {   return bitmap;  } else {   new BitmapAsyncTask().execute(key);   return null;  } } private class BitmapAsyncTask extends AsyncTask<String, Void, Bitmap> {  @Override  protected Bitmap doInBackground(String... url) {   Bitmap bitmap = getBitmapFromUrl(url[0]);   if (bitmap != null) {    mCache.put(url[0],bitmap);   }   return bitmap;  }  private Bitmap getBitmapFromUrl(String url) {   Bitmap bitmap = null;   // 在這里要利用給定的 url 信息從網(wǎng)絡(luò)獲取 bitmap 信息.   return bitmap;  } }