How to Create a android native service and use binder to communicate with it?

Question

My basic task is to create a native service in android and then write a simple native program to test it. lets say i want to write a simple service which return me sum of 2 integers. I have to use binders to talk to it from the program, I have tried to google around but i cant find a precise example. I need to know how to create a native service and find it in the program and if needed in Java also.

Answer 1

If you're creating a normal Android application using the NDK, you can't use Binder because it's not part of the NDK APIs.

Look in the NDK docs/STABLE-APIS.html for the full list of stable APIs, and this thread for an explicit comment by David Turner (the NDK maintainer) that Binder is not a supported API.

https://groups.google.com/forum/?fromgroups=#!topic/android-ndk/1QmVRrNckfM

Your options are:

• Use some other form of IPC in native code - for example a UNIX domain socket
• Do it in Java, using the normal Service and AIDL facilities of the Android SDK. If you wish to combine this with native code you may be able to call up to Java from native code using JNI.
• (Not recommended) Copy the relevant libraries and headers from an Android Open-Source Project; build into your NDK project; and use the APIs. However this is not officially supported and is extremely likely to break your application in future releases because Google are under no obligation to maintain compatibility in such libraries (and frequently do not). It's also very difficult, since you need to find some way to register the service such that the client can find it.

Answer 2

The solution that I found is to use the Binders in native and use the

defaultServiceManager()->addService(
        String16("TestService"),new CalcService());

and then use binders and use following on client side.

sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder = sm->getService(String16("TestService"));

I found examples here on how to do this: https://github.com/gburca/BinderDemo/blob/master/binder.cpp

Answer 3

After studying and coding @ Android NDK, I found The binder API is NOT available in Android NDK. And even if you use android open source for invoking the binder api, maybe you will get permission denied because of the binder security checking.

Here if I want to add a service to System service, I need a system level user group. The detail codes you can find https://github.com/qianjigui/android_system_service_example. It contains C and Java level's client and service, but you need the system permission.