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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