Android NDK开发入门

编写NDK的一般步骤：

1.android studio会自动在打包编译的时候去生成so文件的，但是我在使用c代码测试的时候遇到自动编译出错 Error: Your project contains C++ files but it is not using a supported native build system.
  Consider using CMake or idk-build…….所以我建议还是手动去生成so文件，这时需要让as不自动编译so文件，需要在app module的build.gradle中添加

jni.srcDirs = []

，同时在gradle.properties添加

Android.useDeprecatedNdk=true

2.定义Native方法

在MainActivity下创建sayHello方法

public native String sayHello();

可以新建一个类用来保存相关的Native方法，如HelloJni.java

3.新建jni文件夹，用于存放c文件以及头文件和 .mk文件

在jni目录下创建c文件hello.c

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

//jstring:返回值类型
//Java_所要实现的方法名所在java类用下划线替代点的引用地址_方法名(JNI环境变量 env,JNI环境对象 jobj)
//yuiaragaki.microfun.com.dsaa
jstring Java_yuiaragaki_microfun_com_dsaa_MainActivity_sayHello(JNIEnv *env, jobject thiz)
{
    return (*env)->NewStringUTF(env, "Hello from JNI!");
}

由于手工定义c函数很容易出错，可以借助javah来完成（还没弄明白，之后加上）

4.在jni目录下创建Android.mk文件

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := hello  //ndk编译完之后的so名字  libhello.so
LOCAL_SRC_FILES := hello.c  //指定编译的文件，不需要指定.h源文件，ndk会自动加载
include $(BUILD_SHARED_LIBRARY)

在注释的地方改成自己要编译的文件即可，多个文件写法参照下面

MY_SRC_FILES := $(wildcard $(LOCAL_PATH)/../../../../../Classes/Common/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/GamePlay/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/GridAnimationEditor/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Model/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/UI/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/jansson/*.c)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Algorithm/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Crash/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Effect/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Network/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Resource/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Social/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Common/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Display/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/IOS/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Platform/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Shader/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/UI/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Engine/Data/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Map/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/Scene/*.cpp)
MY_SRC_FILES += $(wildcard $(LOCAL_PATH)/../../../../../Classes/UnitTest/*.cpp)
MY_SRC_FILES := $(MY_SRC_FILES:$(LOCAL_PATH)/%=%)

LOCAL_SRC_FILES := main.cpp \
                   ../../../../../Classes/AppDelegate.cpp
LOCAL_SRC_FILES += $(MY_SRC_FILES)

5.在jni目录下使用idk-build编译c代码

localhost:jni yuiaragaki$ /Users/yuiaragaki/Documents/Android/sdk/ndk-bundle/ndk-build 

编译成功后会在libs 目录下生成libhello.so

6.在java代码中加载so文件即可

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