1、先新建一个JNI目录，并新建一个cpp文件命名jniclass.cpp
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2、在jni目录新建文件，命名为CMakeLists.txt
# Sets the minimum version of CMake required to build your native library.
# This ensures that a certain set of CMake features is available to
# your build.
#指定最小编译cmake的版本
cmake_minimum_required(VERSION 3.6.4)
# Specifies a library name, specifies whether the library is STATIC or
# SHARED, and provides relative paths to the source code. You can
# define multiple libraries by adding multiple add_library() commands,
# and CMake builds them for you. When you build your app, Gradle
# automatically packages shared libraries with your APK.
add_library(
#指定依赖库的名字
# Specifies the name of the library.
jniclass
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
jniclass.cpp
)
# Specifies a path to native header files.
include_directories(include/)
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(
#同上面依赖库的名字
# Specifies the target library.
jniclass
# Links the log library to the target library.
${log-lib})
3、选择LinkC++ Project，选择CMakeLists.txt
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4、在app或module的build.gradle添加
externalNativeBuild {
cmake {
...
version('3.10.2')
}
}
5、调用生成Jni的方法
static {
System.loadLibrary("jniclass");
}
public native String JniGetString();
报错按照提示生成方法
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发现生成的是.c文件，并没有生成方法，可能Android Studio的问题，好，现在先修改.c文件包含在CMakeLists.txt,并同步项目，删除jniclass.c的内容，重新生成，发现已经生成了JNI方法。
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把C文件内容复制到cpp中，然后再把CmakeLists.txt的路径修改成cpp文件，把.c文件删除，并同步工厂，发现cpp报红，按照提示修改
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好然后以后生成的JNI方法都会在cpp文件生成了。
6、调用JNI方法获取字符串
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