如何在Android上管理位图的内存？

Question

I am following this article on Android developer, which quotes :

On Android 2.3.3 (API level 10) and lower, the backing pixel data for a bitmap is stored in native memory. It is separate from the bitmap itself, which is stored in the Dalvik heap. The pixel data in native memory is not released in a predictable manner, potentially causing an application to briefly exceed its memory limits and crash. As of Android 3.0 (API level 11), the pixel data is stored on the Dalvik heap along with the associated bitmap.

There is another article which confused me further :

A Bitmap is a thin wrapper around a native heap memory area that stores pixel data.

I have multiple doubts :

1. What is the difference between Dalvik heap, native heap and native memory ?
2. How is a bitmap different from the pixel data ? My understanding is that any image file (unless it's a vector image) is called bitmap - which is compressed. Android decompresses/decodes this information to render pixels on screen. If I am correct, why do we need the compressed bitmap anymore ?
3. How does a class like BitmapRegionDecoder work ? My understanding is that the entire bitmap is decoded/decompressed first, and then areas out of bound are ignored - this will help in memory efficiency but will not make decoding faster. Am I correct ?
4. What exactly happens when a bitmap is recycled ?

Answer 1

When having an OutOfMemoryError, try the code below.

try {
    bitmap = Bitmap.createBitmap(bm, 0, 0, bm.getWidth(), bm.getHeight(), m, true);
    return bitmap;
} catch (OutOfMemoryError e) {
    bitmap.recycle();
    bitmap = Bitmap.createBitmap(bm, 0, 0, bm.getWidth(), bm.getHeight(), m, true);
    return bitmap;
}