Android Development-NDK development Hello world!

First NDK Program:

The function done here is to use Java to call C code to implement the output of a helloworld~　

Need to download the NDK-Baidu, download and install after the decompression can;

Create a new androidproject, and then create a new JNI package. Create a new Jnitest class under the package.

The structure is as follows:

Start The code in the Jnitest file is as follows:

 Package Com.somnus.androidtest.jni;  Public class jnitest {         publicstaticnative  String helloworldfromjni ();}

Layout file:

<relativelayout xmlns:android= "Http://schemas.android.com/apk/res/android"Xmlns:tools= "Http://schemas.android.com/tools"Android:layout_width= "Match_parent"Android:layout_height= "Match_parent"Android:paddingbottom= "@dimen/activity_vertical_margin"Android:paddingleft= "@dimen/activity_horizontal_margin"Android:paddingright= "@dimen/activity_horizontal_margin"Android:paddingtop= "@dimen/activity_vertical_margin"Tools:context= "Com.somnus.androidtest.MainActivity" > <TextView Android:id= "@+id/tv_hello_jni"Android:layout_width= "Wrap_content"Android:layout_height= "Wrap_content"Android:text= "@string/hello_world"/> <Button android:layout_width= "Wrap_content"Android:layout_height= "Wrap_content"Android:layout_below= "@id/tv_hello_jni"Android:onclick= "OnAction"Android:text= "Click I invoke JNI"/></relativelayout>

Main file code:

 Packagecom.somnus.androidtest;Importcom.somnus.androidtest.jni.JniTest;ImportAndroid.os.Bundle;Importandroid.support.v7.app.ActionBarActivity;ImportAndroid.view.View;ImportAndroid.widget.TextView; Public classMainactivityextendsactionbaractivity {PrivateTextView Tv_hello_jni; @Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);        Setcontentview (R.layout.activity_main); Tv_hello_jni=(TextView) Findviewbyid (R.ID.TV_HELLO_JNI); }     Public voidonAction (View v) {String mstr=Jnitest.helloworldfromjni ();    Tv_hello_jni.settext (MSTR); }}

Go to the chase: ***********************

Start to get our JNI file---->. h file and. mk File

1: Start building our. h file.

The steps are as follows:

Create a new launch configuration icon in the upper left corner. And then I named it: Androidndkdemo

Location is the Javah.exe path of the JDK; Eg:c:\program Files\java\jdk1.8.0_25\bin\javah.exe (This is my JDK path)

Working drectory: ${project_loc} Select from variables

Arguments:-classpath ${project_loc}/bin/classes-d ${project_loc}/jni jni ${java_type_name}

Note In the tab refresh, check the refresh resources upon completion

Common External Tools selected

finally apply;

At this point, you see a directory of more than one JNI folder; The JNI directory has a xxx_xx_xxx_.h file

At this point, in. h is the method in our jnitest. Then we create a new. c file that copies the methods in. h to the. c file, not the parentheses. Do not copy the Jniexport

At this point my. h file is:

Com_somnus_androidtest_jni_jnitest.h

/*Do not EDIT this file-it are machine generated*/#include<jni.h>/*Header for Class Com_somnus_androidtest_jni_jnitest*/#ifndef _included_com_somnus_androidtest_jni_jnitest#define _included_com_somnus_androidtest_jni_jnitest# Ifdef __cplusplusexternC{#endif/** class:com_somnus_androidtest_jni_jnitest * method:helloworldfromjni * Signature: () ljava/lang/string; */jniexport jstring jnicall java_com_somnus_androidtest_jni_jnitest_helloworldfromjni (JNIEnv*, jobject); #ifdef __cplusplus} #endif #endif

Com_somnus_androidtest_jni_jnitest.c

#include <jni.h><string.h>*env, Jobject mstring) {return (*env)- >newstringutf (env, "helloworld! I am from JNI! " );}

New Android.mk File

Local_path: = $ (call my-dir) include $ (clear_vars) #LOCAL_MODULE表示生成的库的名字, the preceding lib and suffix names do not have to be written local_module    := helloworldlocal_src_files:= com_somnus_androidtest_jni_jnitest.cinclude $ (build_shared_library) 

Now we're going to start compiling the code

Open Jnitest.java

or open the external Tools configurations.

A file in new. loaction path to ndk-build.com (download ndk unzipped directory)

Also pay attention to the configuration in refresh and common

OK, run ....

You will see a new libhellowworld.so file in the Libs in the Armeabi folder directory

The final directory structure:

So now we're going back to our jnitest file, write a call method;

Jnitest.java

 Package Com.somnus.androidtest.jni;  Public class jnitest {    static{
Note the name here: HelloWorld is the name we given in the Mk file instead of Libs under the so filename        system.loadlibrary ("HelloWorld");    }      Public Static native String Helloworldfromjni ();}

Then we run the trigger button to run the diagram:

Ok! The end of the ~ ~

Android Development-NDK development Hello world!