performance - Compiling Android project from command line is slow

Question

I'm compiling my (fairly simple, just 5 files with few hundred LOC) app from command line on OSX using:

ant debug

It works. But it works slowly:

BUILD SUCCESSFUL Total time:

26 seconds

Why is that? It takes this much time even if I change only one line in one java file. Most of this time is spent in dex stage (about 20 seconds), which is AFAIK creating Dalvik bytecode. But my friend that also works on the same project on Windows using Eclipse says that compiling takes only a second or two on his machine. Is there anything I can do to speed up this proccess?

Answer 1

I finally found a solution for this! It's a bit of a hack, but it works.

First, go to your ANDROID-SDK/platform-tools directory, then rename dx app to something else, like dextool, and finally create new dx file with contents:

#!/bin/sh
shift
dextool --dex --incremental --no-optimize $@

Replace "dextool" with the name you chose before. This will prepend (undocumented) --incremental attribute to every dex invocation, which will massively decrease build times by dexing only classes that have changed between builds. Now it looks like this:

[dx] Merged dex A (1 defs/11,3KiB) with dex B (359 defs/1253,2KiB). Result is 359 defs/1519,3KiB. Took 0,5s

0.5s instead of 20s is a huge difference!

Edit - few remarks:

• you have to compile your project at least once before using this, because it uses previous classes.dex file
• you can run into problems when using other Android toolchains than ant

UPDATE:

Google released SDK Tools 21.0, which renders above tweak absolete, because it does supports pre-dexing. Finally!