上一篇通过gn构建系统利用部件构建了可执行程序、动态库和配置文件，以及部件内的引用，本篇通过实现跨部件的模块引用，通过实现部件间的使用方法，以此来达到复用三方部件和模块库的目的。
本节以实现两个自定义的部件为例，compdemo3部件为demo3model1_lib模块的动态库部件，compdemo4部件为demo4model1_bin模块为可执行程序部件，以此来描述如何跨部件的引用。
示例部件compdemo3和部件compdemo4完整目录结构如下
├── componentdemo3
│ ├── BUILD.gn
│ ├── bundle.json
│ ├── include
│ │ └── model1.h
│ └── src
│ └── model1.cpp
└── componentdemo4├── BUILD.gn├── bundle.json├── include│ └── model1.h└── src└── model1.cpp1.编写gn脚本/my_test/componentdemo3/BUILD.gn
import("//build/ohos.gni") # 导入编译模板，编译环境等依赖
ohos_shared_library("demo3model1_lib"){ # 动态库模块sources = [ # 模块源码"src/model1.c"]include_dirs = [ # 模块依赖头文件"include"]cflags = []cflags_c = []cflags_cc = []ldflags = []configs = []deps = [] # 部件内部依赖external_deps = [] # 跨部件的依赖，格式为"部件名:模块名"part_name = "compdemo3" # 模块所属部件名称
}注：复制代码时需要删除#及注释，否则无法编译通过2.编写/my_test/componentdemo3/bundle.json
{"name": "@ohos/compdemo3","description": "compdemo3 lib services","version": "3.1","license": "Apache License 2.0","publishAs": "code-segment","segment": {"destPath": "my_test/componentdemo3"},"dirs": {},"scripts": {},"component": {"name": "compdemo3","subsystem": "mycomptest","syscap": [],"features": [],"adapted_system_type": [ "mini", "small", "standard" ],"rom": "10KB","ram": "10KB", "deps": {"components": [],"third_party": [],"hisysevent_config": []},"build": {"sub_component": ["//my_test/componentdemo3:demo3model1_lib"],"inner_kits": [ # 声明部件下那些模块允许在子系统内部使用{"type": "so" # 类型为so"name": "//my_test/componentdemo3:demo3model1_lib" # 模块"header": { # 头信息"heads_files": [ # 头文件名称"model1.h"],"header_base": "//my_test/componentdemo3/include" # 头文件base路径}}],"test": []}}}3.对应src下创建model1.cpp文件，include下创建model1.h文件，文件内容示例如下
model1.h
#ifndef MODEL_1_H
#define MODEL_1_H
#ifdef __cplusplus
#if __cplusplus
extern "C" {
#endif
#endifvoid HelloPrintModel1();#ifdef __cplusplus
#if __cplusplus
}
#endif
#endif
#endifmodel1.cpp
#include <stdio.h>
#include "model1.h"int main(int argc, char **argv)
{HelloPrintModel1();return 0;
}void HelloPrintModel1()
{printf("This component dir is /my_test/componentdemo3 mycomptest->compdemo3->demo3model1_lib\n");
}4.编写gn脚本/my_test/componentdemo4/BUILD.gn
import("//build/ohos.gni") # 导入编译模板，编译环境等依赖
ohos_executable("demo4model1_bin"){ # 可执行模块sources = [ # 模块源码"src/model.cpp"]include_dirs = [ # 模块依赖头文件"include"]cflags = []cflags_c = []cflags_cc = []ldflags = []configs = []deps = [] # 部件内部依赖external_deps = [compdemo3:demo3model1_lib] # 跨部件的依赖，格式为"部件名:模块名"，引入外部部件的模块part_name = "compdemo4" # 模块所属部件名称install_enable = true # 是否安装(缺省默认不安装)
}注：复制代码时需要删除#及注释，否则无法编译通过5.编写/my_test/componentdemo4/bundle.json
{"name": "@ohos/compdemo4","description": "compdemo4 services","version": "3.1","license": "Apache License 2.0","publishAs": "code-segment","segment": {"destPath": "my_test/componentdemo4"},"dirs": {},"scripts": {},"component": {"name": "compdemo4","subsystem": "mycomptest","syscap": [],"features": [],"adapted_system_type": [ "mini", "small", "standard" ],"rom": "10KB","ram": "10KB", "deps": {"components": ["compdemo3"], # 引入外部部件compdemo3"third_party": [],"hisysevent_config": []},"build": {"sub_component": ["//my_test/componentdemo4:demo4model1_bin"],"inner_kits": [],"test": []}}}6.对应src下创建model.cpp文件，include下创建model.h文件，文件内容示例如下
model.h
#ifndef MODEL_H
#define MODEL_H
#ifdef __cplusplus
#if __cplusplus
extern "C" {
#endif
#endifvoid HelloPrint();#ifdef __cplusplus
#if __cplusplus
}
#endif
#endif
#endifmodel.cpp
#include <stdio.h>
#include "model.h"int main(int argc, char **argv)
{HelloPrint();return 0;
}void HelloPrint()
{printf("This component dir is /my_test/componentdemo4, mycomptest->compdemo4->demo4model_bin\n");
}7.在/build/subsystem_config.json文件最后增加如下内容
,"mycomptest": {"path": "my_test","name": "mycomptest"}...
}# 注：以上...}代表内容放在文件最后一级}下注：subsystem_config.json文件此处的"subsystem": "mycomptest"为bundle.json中的"subsystem": "mycomptest"。
8.在/vender/{产品解决方案厂商}/{产品名称}/config.json文件最后增加如下内容，如rk3568芯片则路径为：/vendor/hihope/rk3568/config.json
,{"subsystem":"mycomptest","components": [{"component": "compdemo3","features": []},{"component": "compdemo4","features": []}]}...]
}注：以上...]}代表以上内容放在文件中最后一级数组中注：config.json文件中此处的"subsystem":"mycomptest"为subsystem_config.json文件中的"name": "mycomptest"；"component": "compdemo3"和"component": "compdemo3"为BUILD.gn中的part_name = "compdemo3"和part_name = "compdemo4"。
9.编译
可以使用整编命令
./build.sh --product-name rk3568 --no-prebuilt-sdk也可以使用“–build-target 模块名"单独编译，编译命令如下：
./build.sh --product-name rk3568 --build-target demo4model1_bin --ccache还可以编译模块所在的部件：
./build.sh --product-name rk3568 --build-target compdemo4 --ccache10.烧录到设备后，输入模块命令即可打印
demo4model1_bin后记：
gn 中其他用法
1.成员变量
import("//build/ohos.gni") abc = true
bcd = "123"...if(abc == false){print("This priint is gn key abc is false")
}if(bcd == "123") {print("This priint is gn key bcd is 123")
}if(defined(abc)) { # 变量被定义print("This priint is gn key abc define")
}2.gn定义宏变量
import("//build/ohos.gni")
ohos_shared_library("demo3model1_lib"){...defines = ["SN"] # 定义宏变量方式1cflags = ["-DUUID"] # 定义宏变量方式2 -DXXX，中间无空格cflags_c = []cflags_cc = []ldflags = []configs = []...
}注：复制代码时需要删除#及注释，否则无法编译通过在c代码中使用
#include <stdio.h>
#include "model1.h"int main(int argc, char **argv)
{HelloPrintModel1();return 0;
}void HelloPrintModel1()
{
#ifdef SNprintf("This define SN print");
#endif
#ifdef UUIDprintf("This define UUID print");
#endifprintf("This component dir is /my_test/componentdemo3 mycomptest->compdemo3->demo3model1_lib\n");
}
)
