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

      andoird java programmer, will be java The limitations of the language because the language as a door to the object cannot be like c/c++ The is so easy to invoke hardware-related operations. therefore jni to build such a bridge, so java and C/C++ Languages can be called each other. As a java engineer to c/c++ language is not very familiar, but only to be familiar with the principles and methods of invocation between them, about c/c++ programming is given to c language engineer go ahead.

In this article, we mainly introduce the Ndk/jin construction and basic use method.

First, The construction of the environment

Second, the basic use

Steps:

(1) New Android Project

(2) Declaring the native method in Java

(3) Create a new JNI folder in the 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) Execute "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 parameters in the method that are called in C (Jnienv*,jobject,jint ... ）

2. C calls Java

Call C,c first with Java and 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 execute 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

If still reporting some compilation environment errors, the project transfer to D:\cygwin64\android-ndk-r8c\samples Basic can pass, here I also is not very clear is why, estimate is the problem of path mapping, which big God knows, can share under.

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