Tips and Tricks for handling images in Android

Tyrone NicholasSoftware Engineer8 May 2014

Memory is Scarce

▪~ 1/10 device RAM

▪480 x 800 = 1.5 MB

java.lang.OutOfMemoryError

Android’s solutions

Android heaps

Dalvik

▪JDK

▪Limited

▪Slow

▪Safe

Other

▪Certain system calls

▪Like native

Native

▪NDK

▪Unlimited

▪Fast

▪Unsafe

Put bitmaps in the native heap!

Bitmap.java:

Called from Bitmap.createBitmap()

▪ Eliminated in Android 3.0

Android’s Solution #1

Android’s Solution #2 Need memory

?

Look for unpinne

d memory

Free it

Ashmem

• ashmem_create_region

• ashmem_pin_region

• ashmem_unpin_region

Android’s Solution #2

Draw Allocate Pin Decod

e

Stop drawing

Unpin

Purgeable bitmaps

Android’s Solution #2Howto

Android’s “Solution” #2 • Er, wait a minute…

Android’s Solution #3Bitmap pooling

▪ When doing a decode, specify an old Bitmap object to re-use

Android’s Solution #3Hang on…

Our solution

From the Android NDK…Screw purging. Just screw it.

How to do it (1)

How to do it (2)

Docs can lie

Without a GC…

Caveats• When are you ‘done’ with an image?

• Application-specific

• Nontrivial

• Scrolling

• Caches

ListViews and GridViews

• Beware of flickering!

Other tips

An Image Pipeline

RequestMemoryCacheRead

DiskCacheRead

Network

DiskCacheWrite

Decode

MemoryCacheWrite

Render Transform

WebP

BMP

BMP JPG

JPG

JPG

UI thread Non-UI threads

Using native memory“Naïve native”

• Can’t use for decodes!

▪Devices suck. Servers don’t

▪Consider

Resizing, scaling, and cropping

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