Android 加載大圖片時報OOM的解決方案(源碼)

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 :

1. /**
2. * 加載大圖片工具類：解決android加載大圖片時報OOM異常
3. * 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
4. * @author: 張進
6. * @time:2011/7/28
7. */
8. public class BitmapUtil {
10. public static final int UNCONSTRAINED = -1;
12. /*
13. * 獲得設置信息
14. */
15. public static Options getOptions(String path){
16. Options options = new Options();
17. options.inJustDecodeBounds = true;//只描邊，不讀取數據
18. BitmapFactory.decodeFile(path, options);
19. return options;
20. }
23. /**
24. * 獲得圖像
25. * @param path
26. * @param options
27. * @return
28. * @throws FileNotFoundException
29. */
30. public static Bitmap getBitmapByPath(String path, Options options , int screenWidth , int screenHeight)throws FileNotFoundException{
31. File file = new File(path);
32. if(!file.exists()){
33. throw new FileNotFoundException();
34. }
35. FileInputStream in = null;
36. in = new FileInputStream(file);
37. if(options != null){
38. Rect r = getScreenRegion(screenWidth,screenHeight);
39. int w = r.width();
40. int h = r.height();
41. int maxSize = w > h ? w : h;
42. int inSimpleSize = computeSampleSize(options, maxSize, w * h);
43. options.inSampleSize = inSimpleSize; //設置縮放比例
44. options.inJustDecodeBounds = false;
45. }
46. Bitmap b = BitmapFactory.decodeStream(in, null, options);
47. try {
48. in.close();
49. } catch (IOException e) {
50. e.printStackTrace();
51. }
52. return b;
53. }
57. private static Rect getScreenRegion(int width , int height) {
58. return new Rect(0,0,width,height);
59. }
62. /**
63. * 獲取需要進行縮放的比例，即options.inSampleSize
64. * @param options
65. * @param minSideLength
66. * @param maxNumOfPixels
67. * @return
68. */
69. public static int computeSampleSize(BitmapFactory.Options options,
70. int minSideLength, int maxNumOfPixels) {
71. int initialSize = computeInitialSampleSize(options, minSideLength,
72. maxNumOfPixels);
74. int roundedSize;
75. if (initialSize <= 8) {
76. roundedSize = 1;
77. while (roundedSize < initialSize) {
78. roundedSize <<= 1;
79. }
80. } else {
81. roundedSize = (initialSize + 7) / 8 * 8;
82. }
84. return roundedSize;
85. }
87. private static int computeInitialSampleSize(BitmapFactory.Options options,
88. int minSideLength, int maxNumOfPixels) {
89. double w = options.outWidth;
90. double h = options.outHeight;
92. int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 :
93. (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
94. int upperBound = (minSideLength == UNCONSTRAINED) ? 128 :
95. (int) Math.min(Math.floor(w / minSideLength),
96. Math.floor(h / minSideLength));
98. if (upperBound < lowerBound) {
99. // return the larger one when there is no overlapping zone.
100. return lowerBound;
101. }
103. if ((maxNumOfPixels == UNCONSTRAINED) &&
104. (minSideLength == UNCONSTRAINED)) {
105. return 1;
106. } else if (minSideLength == UNCONSTRAINED) {
107. return lowerBound;
108. } else {
109. return upperBound;
110. }
111. }
114. }

工具類的使用：

1. String path = "/sdcard/test2.jpg";
2. try {
3. Bitmap bitmap = BitmapUtil.getBitmapByPath(path, BitmapUtil.getOptions(path), screenWidth, screenHeight);
4. } catch (FileNotFoundException e) {
5. e.printStackTrace();
6. }