Android:BitmapFactory.decodeStream() 内存不足，400KB 文件和 2MB 可用堆

Question

我的应用在源代码中的以下行遇到 OOM 错误:

image = BitmapFactory.decodeStream(assetManager.open(imgFilename));

就在导致应用因 OOM 错误而终止的分配之前:

(...)
08-05 21:22:12.443: I/dalvikvm-heap(2319): Clamp target GC heap from 25.056MB to 24.000MB
08-05 21:22:12.443: D/dalvikvm(2319): GC_FOR_MALLOC freed <1K, 50% free 2709K/5379K, external 18296K/19336K, paused 58ms
08-05 21:22:14.513: D/dalvikvm(2319): GC_EXTERNAL_ALLOC freed <1K, 50% free 2709K/5379K, external 18296K/19336K, paused 101ms
08-05 21:22:14.903: I/dalvikvm-heap(2319): Clamp target GC heap from 25.073MB to 24.000MB
08-05 21:22:14.903: D/dalvikvm(2319): GC_FOR_MALLOC freed 0K, 50% free 2709K/5379K, external 18312K/19336K, paused 53ms
08-05 21:22:22.843: D/ddm-heap(2319): Heap GC request
08-05 21:22:22.963: I/dalvikvm-heap(2319): Clamp target GC heap from 25.073MB to 24.000MB
08-05 21:22:22.963: D/dalvikvm(2319): threadid=1: still suspended after undo (sc=1 dc=1)
08-05 21:22:22.963: D/dalvikvm(2319): GC_EXPLICIT freed 1K, 50% free 2710K/5379K, external 18312K/19336K, paused 116ms

DDMS 报告了关于堆状态的类似图片:

Heap Size:  5.254 MB
Allocated:  2.647 MB
Free:   2.607 MB
%Used:  50.38%
#Objects    49,028  

单步越过此行会导致 OOM 错误:

08-05 21:26:04.783: D/dalvikvm(2319): GC_EXTERNAL_ALLOC freed <1K, 50% free 2710K/5379K, external 18312K/19336K, paused 57ms
08-05 21:26:05.023: E/dalvikvm-heap(2319): 2097152-byte external allocation too large for this process.
08-05 21:26:05.163: I/dalvikvm-heap(2319): Clamp target GC heap from 25.073MB to 24.000MB
08-05 21:26:05.163: E/GraphicsJNI(2319): VM won't let us allocate 2097152 bytes
08-05 21:26:05.163: D/dalvikvm(2319): GC_FOR_MALLOC freed 0K, 50% free 2710K/5379K, external 18312K/19336K, paused 30ms
08-05 21:26:05.283: D/skia(2319): --- decoder->decode returned false

1. “imgFileName”引用的文件大小在 Windows 上报告为 < 400K。那么为什么 BitmapFactory.decodeStream 会尝试分配 2MB 呢？
2. 为什么似乎有足够的可用空间时会出现 OOM 错误？

此应用面向 Android 2.2 及更高版本。

提前致谢!

Answer 1

Android 库在加载图像方面并不那么聪明，因此您必须为此创建解决方法。

在我的测试中，Drawable.createFromStream 比 BitmapFactory.decodeStream 使用更多的内存。

您可以更改配色方案以减少内存 (RGB_565)，但图像也会降低质量:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Config.RGB_565;
Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);

引用:http://developer.android.com/reference/android/graphics/Bitmap.Config.html

您还可以加载缩放的图像，这将大大减少内存使用量，但您必须知道您的图像不会损失太多质量。

BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 2;
Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);

引用:http://developer.android.com/reference/android/graphics/BitmapFactory.Options.html

要动态定义 inSampleSize，您可能想知道图像大小以做出决定:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
bitmap = BitmapFactory.decodeStream(stream, null, options);
int imageHeight = options.outHeight;
int imageWidth = options.outWidth;

options.inJustDecodeBounds = false;
// recreate the stream
// make some calculation to define inSampleSize
options.inSampleSize = ?;
Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);

您可以根据设备的屏幕尺寸自定义 inSampleSize。要获取屏幕大小，您可以执行以下操作:

DisplayMetrics metrics = new DisplayMetrics();
((Activity) activity).getWindowManager().getDefaultDisplay().getMetrics(metrics);
int screenWidth = metrics.widthPixels;
int screenHeight = metrics.heightPixels;

其他教程:

• http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
• http://developer.android.com/training/displaying-bitmaps/index.html