NDK(23) 使用CMake 构建 c/c++代码库

1.官网

　　https://developer.android.com/studio/projects/add-native-code.html

2.android studio 安装相关工具

1. 在打开的项目中，从菜单栏选择 Tools > Android > SDK Manager。
2. 点击 SDK Tools 标签。
3. 选中 LLDB、CMake 和 NDK 旁的复选框，如图所示.

　　　　

3.新建支持c/c++的项目

1. 在android studio 3.4.1 新建向导里选 Native C++ 模板.

2.选择想要使用的c++标准,如C++14.

3.最后 生成的项目以下:

其中:

• • CMakeLists.txt 是cmake构建工程要用的项目配置文件,相似android.mk.
  • native-lib.cpp是源文件

4.编辑代码,使用本地程序....

4.在现有项目中添加 c/c++库

4.1 建立 jni目录

　　项目名(或者File) ---> 右键 --->  New ---> Folder ---> JNI Folder

4.2 建立 CMakeLists.txt文件 

　　在上一步上建立的jni目录(当前版本目录名是cpp) 右键 ---> New ---> File 输入CMakeLists.txt

4.3 配置CMakeLists.txt 文件

 1 # Sets the minimum version of CMake required to build your native library.
 2 # This ensures that a certain set of CMake features is available to
 3 # your build.
 4 
 5 cmake_minimum_required(VERSION 3.4.1)
 6 
 7 # Specifies a library name, specifies whether the library is STATIC or
 8 # SHARED, and provides relative paths to the source code. You can
 9 # define multiple libraries by adding multiple add.library() commands,
10 # and CMake builds them for you. When you build your app, Gradle
11 # automatically packages shared libraries with your APK.
12 
13 add_library( # Specifies the name of the library.
14              # 本地库名
15              student-lib
16 
17              # Sets the library as a shared library.
18              # 本地库的类型
19              SHARED
20 
21              # Provides a relative path to your source file(s).
22              # 要编译的源文件 ,多个之间用空格.
23              student.cpp school.cpp)
24 
25 # Specifies a path to native header files.
26 include_directories(inc)
27 
28 
29 #添加本地代码依赖的其它系统库.
30 find_library( # Defines the name of the path variable that stores the
31               # location of the NDK library.
32               log-lib
33 
34               # Specifies the name of the NDK library that
35               # CMake needs to locate.
36               log )
37 
38 # Links your native library against one or more other native libraries.
39 target_link_libraries( # Specifies the target library.
40                        student-lib
41 
42                        # Links the log library to the target library.
43                        ${log-lib} )

• 注意CMakeLists.txt中源文件和include的路径引用问题,这里是和源文件同级.
• CMakeLists.txt 经常使用函数含义
• 下面是经常使用的cmake命令.

　　　　cmake命令官网 : https://cmake.org/cmake/help/latest/manual/cmake-commands.7.html 

add_library()	向您的 CMake 构建脚本添加源文件或库 1 add_library( # Specifies the name of the library. 2 native-lib 3 4 # Sets the library as a shared library. 5 SHARED 6 7 # Provides a relative path to your source file(s). 8 src/main/cpp/native-lib.cpp )
include_directories	指定头文件的路径 1 add_library(...) 2 3 # Specifies a path to native header files. 4 include_directories(src/main/cpp/include/)
find_library()	添加引用的NDK 库 1 find_library( # Defines the name of the path variable that stores the 2 # location of the NDK library. 3 log-lib 4 5 # Specifies the name of the NDK library that 6 # CMake needs to locate. 7 log )
target_link_libraries()	连接多个库 1 target_link_libraries( native-lib imported-lib app-glue ${log-lib} )
add_library()	将其它源代码编译到本地库中. 1 add_library( app-glue 2 STATIC 3 ${ANDROID_NDK}/sources/android/native_app_glue/android_native_app_glue.c ) 4 5 # You need to link static libraries against your shared native library. 6 target_link_libraries( native-lib app-glue ${log-lib} )
set_target_properties 和 IMPORTED	IMPORTED不是个函数,只是add_library的参数,添加其余预构建的本地库  而后，您须要使用 set_target_properties() 命令指定库的路径.

4.4 关联Gradle与 CMakeLists.txt　　

　　右键点击您想要关联的模块（例如 app 模块），并从菜单中选择 Link C++ Project with Gradle。关联到以前建立的CMakeLists.txt,点OK.

　　

4.5 完成本地的c/c++代码工做

　　　略...

5.在 Gradle 中使用 CMake 变量

　　https://developer.android.com/ndk/guides/cmake.html#variables

 1 android {
 2   ...
 3   defaultConfig {
 4     ...
 5     // This block is different from the one you use to link Gradle
 6     // to your CMake or ndk-build script.
 7     externalNativeBuild {
 8 
 9       // For ndk-build, instead use ndkBuild {}
10       cmake {
11 
12         // Passes optional arguments to CMake.
13         arguments "-DANDROID_ARM_NEON=TRUE", "-DANDROID_TOOLCHAIN=clang"
14 
15         // Sets optional flags for the C compiler.
16         cFlags "-D_EXAMPLE_C_FLAG1", "-D_EXAMPLE_C_FLAG2"
17 
18         // Sets a flag to enable format macro constants for the C++ compiler.
19         cppFlags "-D__STDC_FORMAT_MACROS"
20       }
21     }
22   }
23 
24   buildTypes {...}
25 
26     ...
27 }

6.指定本地库的cpu架构

　　默认状况下，Gradle 会针对 NDK 支持的 ABI 将您的原生库构建到单独的 .so 文件中，并将其所有打包到您的 APK 中。若是您但愿 Gradle 仅构建和打包原生库的特定 ABI 配置，您能够在模块级 build.gradle 文件中使用 ndk.abiFilters 标志指定这些配置.

 1 apply plugin: 'com.android.application'
 2 
 3 android {
 4     compileSdkVersion 28
 5     defaultConfig {
 6         applicationId "com.example.tocpp5"
 7         minSdkVersion 15
 8         targetSdkVersion 28
 9         versionCode 1
10         versionName "1.0"
11         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
12         // This block is different from the one you use to link Gradle
13         // to your CMake or ndk-build script.
14         externalNativeBuild {
15             // For ndk-build, instead use ndkBuild {}
16             cmake {
17                 // Passes optional arguments to CMake.
18                 arguments "-DANDROID_ARM_NEON=TRUE", "-DANDROID_TOOLCHAIN=clang"
19 
20                 // Sets optional flags for the C compiler.
21                 cFlags "-D_EXAMPLE_C_FLAG1", "-D_EXAMPLE_C_FLAG2"
22 
23                 // Sets a flag to enable format macro constants for the C++ compiler.
24                 cppFlags "-D__STDC_FORMAT_MACROS"
25 
26                 abiFilters 'armeabi-v7a','arm64-v8a'
27 
28             }
29         }
30         ndk {
31             // Specifies the ABI configurations of your native
32             // libraries Gradle should build and package with your APK.
33             abiFilters 'x86', 'x86_64', 'armeabi-v7a','arm64-v8a'
34         }
35     }
36     buildTypes {
37         release {
38             minifyEnabled false
39             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
40         }
41     }
42     externalNativeBuild {
43         cmake {
44             path file('src/main/jni/CMakeLists.txt')
45         }
46     }
47 }
48 
49 dependencies {
50     implementation fileTree(dir: 'libs', include: ['*.jar'])
51     implementation 'androidx.appcompat:appcompat:1.0.2'
52     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
53     testImplementation 'junit:junit:4.12'
54     androidTestImplementation 'androidx.test:runner:1.2.0'
55     androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
56 }

　　在 defaultConfig.externalNativeBuild.cmake {} 块

　　或 

　　defaultConfig.externalNativeBuild.ndkBuild {} 块

　　中配置另外一个 abiFilters 标志。Gradle 会构建defaultConfig.ndk中的 ABI 配置，不过仅会打包在 defaultConfig.cmake或者ndkBuild{} 块中指定的配置。