android studio ndk编程(二)——两种方式编译

序言

  android studio自2.2版本以后,强化了c++的开发能力,可以直接在studio中采用ndk-build或者cmake方式将c/c++代码构建成native libary,然后打包到apk中,比直接用grandle编译c/c++代码更好.本文将介绍这两种方式的ndk开发.

环境配置

需要下载的工具 有:

• The Android Native Development Kit (NDK): 让你能在 Android 上面使用 C 和 C++ 代码的工具集。

• CMake: 外部构建工具。如果你准备只使用 ndk-build 的话，可以不使用它。

• LLDB: Android Studio 上面调试本地代码的工具。

相关的环境配置可参考上一篇博客android studio NDK编程（一）

ndk-build方式编译

在以上环境都配置成功的条件下,ndk-build方式编译c/c++代码,需要以下五个步骤:

• 在android project中在main文件夹下建立与java目录同级的jni目录，如图所示
  

• 在jni目录下新建c/c++文件，文件内容为native方法对应的实现方法。实例为：

/* * 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. * */#include <string.h>#include <jni.h>/* This is a trivial JNI example where we use a native method * to return a new VM String. See the corresponding Java source * file located at: * *   apps/samples/hello-jni/project/src/com/example/hellojni/HelloJni.java */jstringJava_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,                                                  jobject thiz ){#if defined(__arm__)  #if defined(__ARM_ARCH_7A__)    #if defined(__ARM_NEON__)      #if defined(__ARM_PCS_VFP)        #define ABI "armeabi-v7a/NEON (hard-float)"      #else        #define ABI "armeabi-v7a/NEON"      #endif    #else      #if defined(__ARM_PCS_VFP)        #define ABI "armeabi-v7a (hard-float)"      #else        #define ABI "armeabi-v7a"      #endif    #endif  #else   #define ABI "armeabi"  #endif#elif defined(__i386__)   #define ABI "x86"#elif defined(__x86_64__)   #define ABI "x86_64"#elif defined(__mips64)  /* mips64el-* toolchain defines __mips__ too */   #define ABI "mips64"#elif defined(__mips__)   #define ABI "mips"#elif defined(__aarch64__)   #define ABI "arm64-v8a"#else   #define ABI "unknown"#endif    return (*env)->NewStringUTF(env, "Hello from JNI !  Compiled with ABI " ABI ".");}

• 在jni目录中新建Application.mk文件，此文件主要用于将要编译几种类型的so文件。实例代码：

APP_ABI := all

• 在jni目录中新建Android.mk文件。该脚本用来编译c/c++文件。实例代码：

# 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)#编译的模块名,也是activity调用的so库名字LOCAL_MODULE    := hello-jni#需要编译的文件LOCAL_SRC_FILES := hello-jni.c#编译共享库include $(BUILD_SHARED_LIBRARY)

• 将Android.mk文件与grandle关联到一起，Gradle 会将 ndk-build作为一个依赖运行，然后将so打包到 apk 中，编译好的so在目录/build/intermediates/ndkBuild下面。使用方式:鼠标右键要链接的本地库所在的模块，选择Link C++ Project with Gradle，在弹出的对话框中选择Build System为ndk-build，再指定Amdroid.mk的路径点击ok即可.如图所示：
  

以上都完成后，就可以运行项目，会自动编译好so文件。最后附上两张编译完成后demo的结构图。

最后，demo下载地址：链接: https://pan.baidu.com/s/1nuJDP7F 密码: pus9

PS：如果引入第三方so文件，需要在grandle中设置abiFilters。

cmake方式编译

cmake方式编译可参考文章 在 Android Studio 2.2 中愉快地使用 C/C++