建立一個跨平臺可複用C++代碼的實例工程（windows vs2017,android studio 可用）

一直想建立一個可複用c/c++代碼的跨平臺交叉編譯的工程，特別是能分別使用vs2017,android studio , xcode 三種ide來在各自平臺進行編碼。這樣就可以做到算法用c/c++多平臺複用，平臺特有api直接用nactive編碼。最後再結合每個平臺上的webview來實現界面web化，用h5來寫界面。
這樣一套就是，界面用H5,平臺IO訪問接口（除了文件IO,和socket io,因爲c/c++代碼完全可以進行文件io和socketio）用原生代碼,算法用c/c++編寫，做到寫一次交叉編譯到多個平臺，節約編碼時間和跨平臺難度。
最近在github.com就發現了一個開源工程，實現了，用vs2017,anroid studio,xcode 協調編輯同一套代碼，並分發不同平臺的功能，但是他的as工程用的ndk build模式，as 3.1已經不推薦使用了，因爲代碼比較多，遷移起來好像狠麻煩，於是想自己做。得益於as遷移到用CMake來組織JNI工程代碼，好像實現起來也狠順利。
首先新建一個根目錄 Shot4Read。三個平臺的project都放在這個目錄。
結構如下,其中Prj.Android 放的as 工程。Prj.Windows放的vs2017工程。ddmcore放的是可三端複用的c/c++代碼。

H:\DEVTOOLS\project\git\Shot4Read>dir
 驅動器 H 中的卷沒有標籤。
 卷的序列號是 CC73-754C

 H:\DEVTOOLS\project\git\Shot4Read 的目錄

2019-07-02  16:37    <DIR>          .
2019-07-02  16:37    <DIR>          ..
2019-07-02  18:45               419 .gitignore
2019-07-02  18:36    <DIR>          ddmcore
2019-06-28  16:54    <DIR>          Prj.Android
2019-07-02  17:04    <DIR>          Prj.Windows
               1 個文件            419 字節
               6 個目錄 11,622,670,336 可用字節

在Shot4Read目錄建好後，還是空的時候，先用vs2017建立一個MFC對話框工程放到Prj.Windows目錄，然後再建立一個dll工程名字就是ddmcore，放到shot4read目錄。這樣windows工程就建立好了。
然後在shot4read目錄建立一個as的jni工程，放到Prj.Android目錄中。要使as能勾複用dmmcore中的代碼，需要在cpp/CMakeLists.txt文件中改變如下：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)
set(CMAKE_VERBOSE_MAKEFILE ON)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.


#定義CASSDK位置 // 這裏就是導入複用的c/c++代碼目錄。
if(NOT DDMCORE_DIR)
    set( DDMCORE_DIR ${CMAKE_SOURCE_DIR}/../../../../../ddmcore)
endif()
if( IS_DIRECTORY ${DDMCORE_DIR} )
    # Add header file include directories
    include_directories(${DDMCORE_DIR})#添加多目錄的路徑
    # Add block directories
    # 第二個cassdk.out參數用於指定外部文件夾在輸出文件夾中的位置
    add_subdirectory( ${DDMCORE_DIR} cassdk.out)
else()
    message(FATAL_ERROR   "INVALID FOLDER 'CASSDK_DIR'=${DDMCORE_DIR}" )
endif()






add_library( # Sets the name of the library.
        native-lib

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        native-lib.cpp)

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
        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.
        native-lib
        ddmcore-lib
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

然後還需要在ddmcore目錄創建一個CMakeLists.txt,內容如下：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)
set(CMAKE_VERBOSE_MAKEFILE ON)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.




add_library( # Sets the name of the library.
        ddmcore-lib ##引入ddmcore庫

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        apitest.cpp)

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
        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.
        ddmcore-lib #連接ddmcore-lib。
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

這兩個CMakeLists.txt文件編輯好後，刷新as之後，可以發現as直接把ddmcore目錄的代碼自動包含到工程了。如下圖：

至此就成功了。完整代碼可以在阿里雲git庫查看：(點此查看) 這個是windows vs2017 + android studio 分支。。。xcode分支因爲還沒搞定黑蘋果，暫時弄不了。弄好了再創建一個三端分支。。。