本文源码：https://github.com/jt1024/JNIBasicForAndroid

环境

1.Android Studio 3.0
2.gradle-4.1-all
3.android sdk 26

一、在Android Studio 新建安卓工程

二、基本配置

1.配置ndk，如果没有安装，需要先安装ndk。ndk.dir=“ndk实际路径”

ndk01.jpg

2.改写build.gradle文件

ndk02.jpg
3.创建cpp文件夹、login_lib.cpp、CMakeLists.txt
ndk03.jpg

三、编写代码

1.编写C++文件 login_lib.cpp
路径：NDKSecondDemo/app/src/main/cpp/login_lib.cpp

//
// Created by tao1024 on 2018/3/15.
//

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
#include "string.h"
/* Header for class com_tao_ndkseconddemo_Java2CLogin */

extern "C"
/*
 * Class:     com_tao_ndkseconddemo_Java2CLogin
 * Method:    login
 * Signature: (Ljava/lang/String;Ljava/lang/String;I)Ljava/lang/String;
 */
JNIEXPORT jstring

JNICALL
Java_com_tao_ndkseconddemo_Java2CLogin_login(JNIEnv *env, jobject instance, jstring username,
                                             jstring password, jint authcode) {
    const char *resultMessage;
    if (authcode == 888) {
        const char *cStr;
        const char *pStr;
        jboolean isCopy;
        cStr = env->GetStringUTFChars(username, &isCopy);
        pStr = env->GetStringUTFChars(password, &isCopy);
        int reUsername = strcmp(cStr, "admin");
        int rePassword = strcmp(pStr, "1234");
        if (reUsername == 0 && rePassword == 0) {
            resultMessage = "success login !";
        } else {
            resultMessage = "error username or error password";
        }
    } else {
        resultMessage = "error authcode";
    }
    return env->NewStringUTF(resultMessage);
}

2.编写Jave文件 Java2CLogin
路径：NDKSecondDemo/app/src/main/java/com.tao.ndkseconddemo.Java2CLogin

package com.tao.ndkseconddemo;

/**
 * 作者： 麦典威
 * 修改时间：2018/3/15 8:07
 * 版权声明：www.ekwing.com
 * 功能： ${TODO}
 */


public class Java2CLogin {
    static {
        System.loadLibrary("login_lib");
    }

    /**
     * 带参数的 native 函数
     *
     * @param username 用户名
     * @param password 密码
     * @param authcode 验证码
     * @return
     */
    public native String login(String username, String password, int authcode);
}

3.编写Activity文件 MainActivity
路径：NDKSecondDemo/app/src/main/java/com.tao.ndkseconddemo.MainActivity

package com.tao.ndkseconddemo;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private EditText edtUsername, edtPassword, edtAuthcode;
    private Button btnLogin;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
        edtUsername = findViewById(R.id.edt_username);
        edtPassword = findViewById(R.id.edt_password);
        edtAuthcode = findViewById(R.id.edt_authcode);
        btnLogin = findViewById(R.id.btn_login);

        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = edtUsername.getText().toString().trim();
                String password = edtPassword.getText().toString().trim();
                String authcodeStr = edtAuthcode.getText().toString().trim();
                int authcode = Integer.parseInt(authcodeStr.equals("") ? "0" : authcodeStr);
                String result = new Java2CLogin().login(username, password, authcode);
                Log.e(TAG, "Java调用C获取的结果是：" + result);
                Toast.makeText(MainActivity.this, result, Toast.LENGTH_LONG).show();
            }
        });
    }

}

4.编写 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    tools:context="com.tao.ndkseconddemo.MainActivity">

    <EditText
        android:id="@+id/edt_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入用户名(admin)" />

    <EditText
        android:id="@+id/edt_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入密码(1234)" />

    <EditText
        android:id="@+id/edt_authcode"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入验证码(888)" />

    <Button
        android:id="@+id/btn_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="登陆" />

</LinearLayout>

5.编写CMakeLists.txt文件，以后如果编写其他jni类，只需替换里面的“login_lib”

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
             login_lib

             # Sets the library as a shared library.
             SHARED

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

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

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 )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       login_lib

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

四、编译

点击build——>Rebuild Project 或 Make Progject

ndk04.png

编译结束之后，回编译出对应的 .so 文件，如图

ndk04.jpg

五、运行程序

ndk05.jpg