android ndk编程学习记录-1

• 使用cmake配合CMakeLists.txt脚本进行编译的C/C++编程要将源码文件在CMakeLists.txt中添加到工程中才会有对应的代码提示

• build.grale的配置

android{
    defaultConfig{
        externalNativeBuild {
            cmake{
                abiFilters "armeabi-v7a", "arm64-v8a"
            }
        }
        sourceSets {
            main {
                jniLibs.srcDirs = ['libs']
            }
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    ...
}

• 注意：sourceSets必须配置，不然在运行时会抛出java.lang.UnsatisfiedLinkError: dlopen failed: library "xxx.so" not found的异常

• 注意这里关于LIB_DIR的定义，在CMakeLists.txt中编译系统会传入诸多的变量，我们可以在cmake脚本中可以使用，比如这里的CMAKE_CURRENT_SOURCE_DIR表示的就是脚本所在目录，ANDROID_ABI表示的就是打包对应的ABI等等
• 使用预编译好的.so库的时候需要将.so在脚本中导入并作为依赖通过target_link_libraries设置给目标项目，这里引入的方式是通过add_library与set_target_properties两个方法配合

cmake_minimum_required(VERSION 3.4.1)
#project(pngCompress)

set(SRC_DIR src/main/jni)
set(LIB_DIR ${CMAKE_CURRENT_SOURCE_DIR}/libs/${ANDROID_ABI})
include_directories(${SRC_DIR}/include)


add_library(libpng SHARED IMPORTED)
set_target_properties(libpng PROPERTIES IMPORTED_LOCATION ${LIB_DIR}/libpng.so)

add_library(pngcompress SHARED ${SRC_DIR}/pngcompress.cpp)

find_library(
        log-lib
        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log)

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
        pngcompress
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib} libpng)