android studio 的jni 动态调用

直接上源码：

package com.mayj.dyhellojni;

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

public class MainActivity extends AppCompatActivity {
    TextView textView;
    TextView textViewSum;

    static {
        System.loadLibrary("FirstJni");
    }

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

    @Override
    protected void onResume() {
        super.onResume();
        textView = findViewById(R.id.text_id);
        textViewSum = findViewById(R.id.text_sum);
        textView.setText(JniClient.getInstance().getStr());
        textViewSum.setText("" + JniClient.getInstance().addInt(2, 4));
    }
}

package com.mayj.dyhellojni;

/**
 * Created by Administrator on 2018/5/20 0020.
 */

public class JniClient {
    public native String getStr();
    public native int addInt(int a, int b);

    static private JniClient instance = null;
    static public JniClient getInstance(){
        if (null == instance){
            instance = new JniClient();
        }
        return instance;
    }
}

Android.mk内容：

# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := FirstJni

LOCAL_SRC_FILES := JniClient.c

include $(BUILD_SHARED_LIBRARY)

Application.mk内容：

APP_MODULES := FirstJni
APP_STL := stlport_static

APP_PLATFORM=android-16

APP_OPIM :=debug

APP_ABI := armeabi armeabi-v7a

JniClient.c源码如下：

#include <stdlib.h>  
#include <string.h>  
#include <stdio.h>  
#include <jni.h>  
#include <assert.h>  
  
#define JNIREG_CLASS "com/mayj/dyhellojni/JniClient"//指定要注册的类  
  
jstring get_str(JNIEnv* env, jobject thiz)
{  
    return (*env)->NewStringUTF(env, "Hello, 动态注册JNI");
}  
  
jint add_int(JNIEnv* env, jobject jobj, jint num1, jint num2){  
    return num1 + num2;  
}  
  
/**  
* 方法对应表  
*/  
static JNINativeMethod gMethods[] = {  
        {"getStr", "()Ljava/lang/String;", (void*)get_str},  
        {"addInt", "(II)I", (void*)add_int},  
};  
  
/*  
* 为某一个类注册本地方法  
*/  
static int registerNativeMethods(JNIEnv* env  
        , const char* className  
        , JNINativeMethod* gMethods, int numMethods) {  
    jclass clazz;  
    clazz = (*env)->FindClass(env, className);  
    if (clazz == NULL) {  
        return JNI_FALSE;  
    }  
    if ((*env)->RegisterNatives(env, clazz, gMethods, numMethods) < 0) {  
        return JNI_FALSE;  
    }  
  
    return JNI_TRUE;  
}  
  
  
/*  
* 为所有类注册本地方法  
*/  
static int registerNatives(JNIEnv* env) {  
    return registerNativeMethods(env, JNIREG_CLASS, gMethods,  
                                 sizeof(gMethods) / sizeof(gMethods[0]));  
}  
  
/*  
* System.loadLibrary("lib")时调用  
* 如果成功返回JNI版本, 失败返回-1  
*/  
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved) {  
    JNIEnv* env = NULL;  
    jint result = -1;  
    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {  
        return -1;  
    }  
    assert(env != NULL);  
    if (!registerNatives(env)) {//注册  
        return -1;  
    }  
    //成功  
    result = JNI_VERSION_1_4;  
    return result;  
} 

module的 build.gradle 要修改：

把def ndkDir = 'C:\\Users\\Administrator\\AppData\\Local\\Android\\Sdk\\ndk-bundle' 改成你的ndk路径

apply plugin: 'com.android.application'

def ndkDir = 'C:\\Users\\Administrator\\AppData\\Local\\Android\\Sdk\\ndk-bundle'

android {
    compileSdkVersion 26
    defaultConfig {
        applicationId "com.mayj.dyhellojni"
        minSdkVersion 19
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
    }

    sourceSets.main{
        jni.srcDirs=[]//禁用as自动生成mk

        //以下两种写法都是一样的效果
        jniLibs.srcDir 'src\\main\\libs'
//        jniLibs.srcDirs = ['src/main/libs']
    }


    clean.dependsOn 'cleanNative'
    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn buildNative
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

task buildNative(type: Exec, description: 'Compile JNI source via NDK') {
    commandLine "$ndkDir\\ndk-build.cmd",
            '-C', file('src\\main\\jni').absolutePath, // Change src/main/jni the relative path to your jni source
            '-j', Runtime.runtime.availableProcessors(),
            'all',
            'NDK_DEBUG=1'
}
task cleanNative(type: Exec, description: 'Clean JNI object files') {
    commandLine "$ndkDir\\ndk-build.cmd",
            '-C', file('src\\main\\jni').absolutePath, // Change src/main/jni the relative path to your jni source
            'clean'
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
}

源码路径：

https://download.csdn.net/download/myjie0527/10426347