Eclipse集成NDK

Sooner or later in your Android game development foray you may find the need to have some code that runs faster. It turns out that Android code written in C runs 10-100 times as fast as its Java counterpart. I can verify this, as I've already moved a few major components in my newest 3D game engine into native land. That's quite a boost but let's face it - C is a pain in the ass and while Eclipse is great for Java, it's not for C, right? Wrong. Here's how to set up a super speedy NDK development environment.

First of all, Eclipse can do way more than just Java. Java is what it's great at and what it was designed for but the architecture makes it so that it can handle any language effectively, including C. There is a component called CDT that allows for C/C++ Development in Eclipse. I'm getting ahead of myself, though. Here's what you need:

Android NDK (Native Development Kit)
Eclipse CDT (C Development Tooling)
If you're in Windows, you'll need Cygwin with the devel packages installed (Especially GCC and Make)

Here's what you need to do:

Install all 3 of those things. I like to install my NDK to c:\Android_NDK. I'll refer to that dir for the rest of this article.
Get acquainted with the NDK. You need to configure each project as an "app" in the c:\Android_NDK\apps dir. Just take a look at the examples. They work and are thorough.

How to test your NDK:
Run cygwin
cd /cygdrive/c/Android_NDK
make APP=hello-jni

It should compile without errors. If you are missing GCC or Make or any other dev packages, you will want to run your Cygwin setup again and check to make sure that all of the development packages are installed. If you have strange errors, I suggest reporting them in the NDK user's group.

Once your NDK is working, you can add an app for your project and set up the basic native framework for your project. Please refer to the examples for this part. You will need a specific build file that tells the compiler what sources to compile. JNI code is usually located in your Android project's jni folder. A file called Android.mk will need to be in there which instructs the compiler on what to compile.

After you get the basic configuration done, you will want to start writing some C. NDK uses Java's standard JNI bindings to work. All of the existing documentation on JNI should apply from this point forward. What to code is beyond the scope of this article.

Now for the good part

If you've done any NDK work, you're probably used to using a text editor or vim or some other editor to edit your C/CPP then running make APP=myapp every time to build, then clicking refresh on your project in Eclipse and then hoping that the shared object library file that gets deployed is current. What a pain in the ass! There's a much, much better way.

Now that you have CDT installed, you can edit all of your C/C++ right from Eclipse. If you right click on a C/CPP source file, just pick Open With--C/C++ Editor and it will use the CDT editor. Much nicer! It won't be able to figure out what the code is doing because it's not compiling it, but it will make editing nice and all in one spot.

Building is a snap as well. Ever used builders in Eclipse? They are configurable triggers that will execute what you configure and refresh resources for you. Make sure you know if you're on the old r3 NDK (upgrade if you are - you should be on r4) and if so, I put different instructions in this list for the different versions. Here's how I set mine up:

Right click on your project, pick properties.
Select "builders" from the left-hand list.
Click "New..." on the right side.
Select "Program" as the configuration type.
I name mine "Native Builder"
Location - c:\cygwin\bin\bash.exe
Working Directory - c:\cygwin\bin
Arguments -
(for NDK r3):
--login -c "cd /cygdrive/c/Android_NDK && make APP=myapp"
(for NDK r4):
--login -c "cd /cygdrive/c/<myapp_project_dir> && /cygdrive/c/Android_NDK/ndk-build"
Make sure you have the two hyphens before login and the quotes after the hyphen-c
Now go to the refresh tab
Check "Refresh resources upon completion"
Select "Specific resources"
Click on the "Specify resources" button and select your project's lib directory.
Check "Recursively include sub-folders"
Now go to the build options tab
Check "Allocate Console"
Check "Launch in background"
Check "Run the builder After a Clean"
Check "Run the builder During manual builds"
Check "Run the builder During auto builds"
Check "Specify working set of relevant resources"
Click on "Specify Resources"
Select your project's JNI directory and all files within.
Now click OK on the bottom.

The assumption here is that cygwin is installed to c:\cygwin, NDK is in c:\Android_NDK and your project is called "myapp". Change where appropriate.

What did you just do?! You made it so that any time you edit any files within your JNI directory and you save them, Eclipse will run the NDK Builder for you via Cygwin and show the compile output in your console. When it finishes, it will refresh your output (lib) directory which will trigger ADT to compile a new APK for you and YOU ARE GOOD TO GO!

This seriously sped me up while working on my current project. I hope you can all benefit from it!