Basic introduction to "Android Advanced" NDK/JNI programming technology

as a andoird java Program Ape, it is subject to the limitations of the Java language. Because a language that is a door-to-object cannot easily invoke hardware-related operations as a C + + + . So JNI builds a bridge that allows the Java and C + + languages to invoke each other.

As a Javaproject teacher, the C /C + + language is not very familiar, but only need to familiarize themselves with the principles and methods of the call between them, programming about C / D Language project teacher go ahead.

In this article, we mainly introduce Ndk/jin construction and basic usage.

First, The construction of the environment

Second, the main use

Steps:

(1) New Androidproject

(2) Declaring the native method in Java

(3) Create a new JNI directory in project (use Javah test to generate the header file, write C code)

(4) Write the Android.mk file (a configuration file that tells the NDK how to compile C code)

   Local_path: = $ (call My-dir) include $ (clear_vars) local_module    : = test-jnilocal_src_files: = Test-jni.clocal_ Ldlibs+=-lloginclude $ (build_shared_library)

(5) Run "Ndk-build" to generate a dynamic library (you can also generate a dynamic library using run in Eclipse)

(6) Java code "load" Dynamic library, invoke dynamic library

1. Java calls C

Java calls native method (Class param)

The number of parameters in the method that will be called in C (Jnienv*,jobject,jint ... ）

2. C calls Java

Call C with Java first. C then callback

jniexport void Jnicall java_com_ndk2_test_providebean_callhi (jnienv *env,jobject obj) { Char*classname = "Com/ndk2/test/providebean"; Jclass Clazz;clazz = (*env)->findclass (env, classname); if (clazz = = 0) { Logi ("Can not find Class");} else {Logi ("Find the Class");} Jmethodid mid = (*env)->getmethodid (env, Clazz, "Showhi", "() V"), if (mid = = 0) {Logi ("Can not Find Method");} else {LOG I ("Find Method");} (*env)->callvoidmethod (env, obj, mid);} Jniexport void Jnicall java_com_ndk2_test_providebean_calladd (jnienv *env,jobject obj) {char*classname = "com/ndk2/  Test/providebean "; Jclass Clazz;clazz = (*env)->findclass (env, classname); if (clazz = = 0) {Logi (" Can not find Class ");} else {Logi ("Find the Class");} Jmethodid mid = (*env)->getmethodid (env, Clazz, "Showadd", "(II) V"), if (mid = = 0) {Logi ("Can not Find Method");} else { Logi ("Find Method");} (*env)->callvoidmethod (env, obj, Mid, 6, 7);} 

You also configure the environment before you run the project:

C + + Bulid Build command:bash D:\cygwin64\android-ndk-r8c\ndk-build

C + + general/paths and Symbols/gnu C add D:\cygwin64\android-ndk-r8c\platforms\android-14\arch-arm\usr\include

Suppose you are still reporting some errors in the compilation environment. Transfer project to D:\cygwin64\android-ndk-r8c\samples Basic can be passed, here I am not very clear why, is expected to be a path mapping problem, which the great God knows, can share under.

Basic introduction to "Android Advanced" NDK/JNI programming technology