通过CmakeLists.txt或Android.mk向Android工程添加c++代码
一、Cmake Build /main/.Java->main/.cpp->app/CmakeLists.txt->app/build.gradle
1.创建java侧接口文件
目的是以后将这些native方法当java方法使用，java侧只关心这几个方法。
publicclassTestJNI{
//加载.so库：
//1.加载之后，sayHello就与so库里面的cpp中的函数对应起来，不需要头文件
static{
System.loadLibrary("TestJNI");
}
Public static native String sayHello();
}
2.根据.h文件的函数命名规则编写cpp文件
3.编译java接口文件对应的.h文件，根据.h文件的函数名称实现对应的cpp文件，cpp文件一般放在main文件夹下的cpp文件夹下
根据Java方法编译出JNI的.h头文件。命令行进入到java代码目录下，即app/src/main/java，输入以下命令：
javah -jni xxxx.com.jnitech.JniInterface
JniInterface为class的类名，然后在对应java文件的目录下生成对应的.h文件
4.在app文件夹下新建CmakeLists.txt文件添加源文件依赖关系
4.1 添加源代码依赖：
add_library( # Specifies the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
src/main/cpp/native-lib.cpp )
4.2 添加原生API和库依赖，例如下面将原生log库作为依赖保存到log-lib变量
原生库依赖：
find_library( # Defines the name of the path variable that stores the
# location of the NDK library.
log-lib
# Specifies the name of the NDK library that
# CMake needs to locate.
log )
# Links your native library against one or more other native libraries.
target_link_libraries( # Specifies the target library.
native-lib
# Links the log library to the target library.
${log-lib} )
原生API依赖：
add_library( app-glue
STATIC
${ANDROID_NDK}/sources/android/native_app_glue/android_native_app_glue.c )
# You need to link static libraries against your shared native library.
target_link_libraries( native-lib app-glue )
4.3 添加已经编译好的.so库依赖
add_library( imported-lib
SHARED
IMPORTED )
set_target_properties( # Specifies the target library.
imported-lib
# Specifies the parameter you want to define.
PROPERTIES IMPORTED_LOCATION
# Provides the path to the library you want to import.
imported-lib/src/${ANDROID_ABI}/libimported-lib.so )
include_directories( imported-lib/include/ ) #已经编译好的库可能有头文件也要引入
4.5 如果自身的.so库用到了上述的依赖API或库还需要关联到自身库中
target_link_libraries( #自身的cpp将要生成的.so库文件名
native-lib
#依赖的其他的库名
imported-lib #外部库
app-glue #原生API
${log-lib} ) #原生库
在app的build.gradle里面关联CmakeLists.txt
// Encapsulates your external native build configurations.
externalNativeBuild {
// Encapsulates your CMake build configurations.
cmake {
// Provides a relative path to your CMake build script.
path "CMakeLists.txt"
}
}
默认是NDK支持的ABI全部打包到APK中，通过下面的配置可以打包指定ABI类型的.so库到APK中
defaultConfig {
...
externalNativeBuild {
cmake {...}
// or ndkBuild {...}
}
ndk {
// Specifies the ABI configurations of your native
// libraries Gradle should build and package with your APK.
abiFilters 'x86', 'x86_64', 'armeabi', 'armeabi-v7a',
'arm64-v8a'
}
}
二、Ndk Build main/.Java->main/jni/.cpp->PROJECT_PATH/jni/Android.mk->PROJECT_PATH/Application/mk
1.创建java接口文件，如上述第一点
2.在main目录下右键–>New–>Folder–>JNI Folder，再创建cpp文件，如上述第二点
Java_com_huawei_hicode_ndk_JniUtils_getStringFromC(
JNIEnv *env,
jclass type) {
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}
3.在工程目录下先创建jni文件夹，再创建Application.mk如下：
APP_STL := c++_static #默认提供最小运行时库，这里是添加c++静态库，使string\vector\iostream能够包含进来
4.在app目录或者上述jni目录创建Android.mk目录。如下：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := TestJNI
LOCAL_SRC_FILES := $(LOCAL_PATH)/../app/src/main/jni/com_huawei_hicode_ndk_JniUtils.cpp
include $(BUILD_SHARED_LIBRARY)
5.在app/build.gradle中添加：
externalNativeBuild {
ndkBuild {
path '../jni/Android.mk'
}
}