在Android中:
1.一個進程的內存可以由2個部門組成:java 施用內存 ,C 施用內存 ,這兩個內存的和必需小於16M,不然就會出現各人熟悉的OOM,這個就是熬頭種OOM的情況。
2.一朝內存分配給Java後,以後這塊內存縱然開釋後,也只能給Java的施用,這個估計跟java虛擬機裡把內存分成好幾塊進行緩存的原因有關,反正C就別想用到這塊的內存了,所以要是Java突然占用了一個大塊內存,縱然很快開釋了:
C能施用的內存 = 16M - Java某一瞬間占在校大學生創業點子用的最大內存。
而Bitmap的生成是路程經過過程malloc進行內存分配的,占用的是C的內存。
Code :
- /**
- * 加載大圖片工具類:解決android加載大圖片時報OOM異常
- * 解決原理:先設置縮放選項,再讀取縮放的圖片數據到內存,規避了內存引起的OOM
- * @author: 張進
-
- * @time:2011/7/28
- */
- public class BitmapUtil {
-
- public static final int UNCONSTRAINED = -1;
-
- /*
- * 獲得設置信息
- */
- public static Options getOptions(String path){
- Options options = new Options();
- options.inJustDecodeBounds = true;//只描邊,不讀取數據
- BitmapFactory.decodeFile(path, options);
- return options;
- }
-
-
- /**
- * 獲得圖像
- * @param path
- * @param options
- * @return
- * @throws FileNotFoundException
- */
- public static Bitmap getBitmapByPath(String path, Options options , int screenWidth , int screenHeight)throws FileNotFoundException{
- File file = new File(path);
- if(!file.exists()){
- throw new FileNotFoundException();
- }
- FileInputStream in = null;
- in = new FileInputStream(file);
- if(options != null){
- Rect r = getScreenRegion(screenWidth,screenHeight);
- int w = r.width();
- int h = r.height();
- int maxSize = w > h ? w : h;
- int inSimpleSize = computeSampleSize(options, maxSize, w * h);
- options.inSampleSize = inSimpleSize; //設置縮放比例
- options.inJustDecodeBounds = false;
- }
- Bitmap b = BitmapFactory.decodeStream(in, null, options);
- try {
- in.close();
- } catch (IOException e) {
- e.printStackTrace();
- }
- return b;
- }
-
-
-
- private static Rect getScreenRegion(int width , int height) {
- return new Rect(0,0,width,height);
- }
-
-
- /**
- * 獲取需要進行縮放的比例,即options.inSampleSize
- * @param options
- * @param minSideLength
- * @param maxNumOfPixels
- * @return
- */
- public 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;
- }
- }
-
-
- }
工具類的使用:
- String path = "/sdcard/test2.jpg";
- try {
- Bitmap bitmap = BitmapUtil.getBitmapByPath(path, BitmapUtil.getOptions(path), screenWidth, screenHeight);
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- }