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，也隻能給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瞭，所以要是Java突然占用瞭一個大塊內存，縱然很快開釋瞭：
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，規避瞭內存引起的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;//隻描邊，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();
}