Cmake编写JNI

 调用两个库

CMakeLists.txt

//把那种大段的注释去掉了
cmake_minimum_required(VERSION 3.4.1)


add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp )

add_library( # Sets the name of the library.
             nativeSecond-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/nativeSecond-lib.cpp )

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

target_link_libraries( # Specifies the target library.
                     nativeSecond-lib

                     # Links the target library to the log library
                     # included in the NDK.
                     ${log-lib} )

native-lib.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring

JNICALL
Java_com_example_aplex_cantest_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

nativeSecond-lib.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring

JNICALL
Java_com_example_aplex_cantest_MainActivity_stringFromJNI22(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = "Hello Second from C++";
    return env->NewStringUTF(hello.c_str());
}

MainActivity.java

package com.example.aplex.cantest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
        System.loadLibrary("nativeSecond-lib");
    }
    Button bt;
    TextView tv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Example of a call to a native method
        tv = (TextView) findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());


        bt = (Button)findViewById(R.id.bt);
        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                tv.setText(stringFromJNI22());
            }
        });
    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();
    public native String stringFromJNI22();
}