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Android JNI practice use Android Studio 1.5
=================



1.creata an [empty activiry] android project.
2.set textview id to TextView1.
3.add below code in MainActivity.java, before onCreate()
  --
  static {
System.loadLibrary("JniDemo");
}
public native String getStringFromNative();
--

4.use Terminal, switch path to app/src/main/java
  submit command to create com_usi_testjni_MainActivity.h
  javah -jni com.usi.testjni.MainActivity
 
5.create JNI folder under main.
  Project-> Testjni > app > main, right click >new > folder > JNIfolder
  move main\com_usi_testjni_MainActivity.h
  to
  jni\com_usi_testjni_MainActivity.h

6.create HelloNDK.c undr jni folder
  jni > right click > new > file > file name HelloNDK.c
  add below code in HelloNDK.c
  -- 
#include <com_usi_testjni_MainActivity.h>
JNIEXPORT jstring JNICALL Java_com_usi_testjni_MainActivity_getStringFromNative
        (JNIEnv * evn, jobject obj)
{
    return (*evn)->NewStringUTF(evn,"Hello NKD demo!!!!!!!!!!!!");
}
  --

7.add ndk.dir,sdk.dir in local.properties
  open Testjni > local.properties, add
  ndk.dir=C\:\\Users\\mark\\AppData\\Local\\Android\\sdk\\ndk-bundle
  sdk.dir=C\:\\Users\\mark\\AppData\\Local\\Android\\sdk

8.add android.useDeprecatedNdk=true under Testjni >gradle.properties 
 open Testjni > gradle.properties, add
 android.useDeprecatedNdk=true
 
9.add ndk module name in app > build.gradle
  open Testjni > app > build.gradle, add
  --
          ndk{
            moduleName "JniDemo"
        }
  --
  after         versionName "1.0"

10.add code to show ndk message in MainActivity.java
   open MainActivity.java, add below code in onCreate function.
   --
        TextView tmpview = (TextView)findViewById(R.id.TextView1);
        tmpview.setText(getStringFromNative());
   -- 
  
11.now android app can call c/c++ function via JNI.
     On device, result show as below:
   

Note:  
.if javah can not find ,please check your java path and add to PATH fow windows platform.
  my java is locate
  c:\Program Files\Java\jdk1.7.0_75\bin\
.if [Error: Cannot determine signature for Bitmap message] show , try below to solve it
solve method:
javah -classpath C:\Users\mark\AppData\Local\Android\sdk\platforms\android-22\android.jar;. com.usi.imagerpreview.MainActivity

.default SDK path
C:\Users\mark\AppData\Local\Android\sdk

.default NDK path
C:\Users\mark\AppData\Local\Android\sdk\ndk-bundle