Android NDK Development

Android NDK Development
1. Introduction to JNI is the Java Native Interface. it defines a way for managed code (written in the Java programming language) to interact with native code (written in C/C ++ ).
JNI (Java Local interface): defines a method for Java code to interact with C code or Dynamic Shared Libraries (Dynamic Shared library.
Call method:

C code generates a. so dynamic shared library through compilation for java code calls.

2. Introduction to NDK development NDK is a C/C ++ code Development Toolkit provided by Google for Android, including GCC compilers and header files related to various platforms (arm, X86, MIPS, cross-compiled platform-related files. You can download it from the google website. 1. Configure the downloaded ndk resource package to unmount the downloaded ndk package. android-ndk-r9b-windows-x86.zip
Preferences --> Android --> NDK, configure the location of the ndk
2. Demonew is developed and used as a general Android project TestJni;
Right-click the project, choose Android Tools --> Add Native Support, and enter the name of the dynamic library to be generated: TestJni;
In this case, a jni folder is added, including a file TestJni. c and Android. mk.
Android. mk:
LOCAL_PATH: = $ (call my-dir)
Include $ (CLEAR_VARS)
LOCAL_MODULE: = TestJni
LOCAL_SRC_FILES: = TestJni. c
Include $ (BUILD_SHARED_LIBRARY)

 

 

Note:

BUILD_SHARED_LIBRARY: indicates that the compilation target is a dynamic shared library, that is, the. so file is generated.

LOCAL_MODULE: name of the compilation target.

LOCAL_SRC_FILES: Compile the source file

 

TestJni. c is the local C code. In this example, only the return of a Hello string is added. The method name is defined so that the java code can find the corresponding native code. The specification is as follows: java + package name + class + Method, otherwise it cannot be found.
Of course, there can be another method ing method that can realize the ing between java and C methods, which is not described in detail here.

 

jstring Java_com_pingtech_testjni_TestJni_sayHello( JNIEnv* env,        jobject thiz ){return (*env)->NewStringUTF(env, "Hello from JNI !");}

3. JNI java code

public class TestJni{public static native String sayHello();static{System.loadLibrary("TestJni");}}

To use a static code block, first load the TestJni. so dynamic shared library. sayHello is the local method in C, and add a native modifier. We can use TestJni. sayHello (); To call C code in Java code. 4. Compile and run the Project build all to detect local code errors and generate the. so Library (in lib/armeabi, for the arm platform, you can compile it on other platforms by configuring it ).