Android Studio向項目添加C/C++原生代碼

向項目添加C/C++代碼分爲兩種狀況:

• 一種是建立支持C/C++代碼的新項目
• 一種是向以前不支持的項目中添加C/C++代碼

建立支持C/C++原生代碼的新項目

1.1 下載NDK和構建工具

1.2 建立支持C/C++的新項目

菜單欄-File-new-new Project,新建項目

必定記得勾選箭頭指向的那個選項，否則建立出來的項目不會支持C/C++. 而後一路next。

這裏可能和咱們平時建立項目不同，可是這裏默認的就行了。點擊Finish。最後建立的項目目錄結構

咱們發現箭頭所指的兩處就是相對於普通項目多了的兩個文件。 External Build Files組用於存放CMake或ndk-build的構建腳本。 和Gradle須要build.gradle文件來指示如何構建應用同樣，CMake和ndk-build依照一個構建腳原本構建原生庫。 Android Studio建立了一個CMake構建腳本CMakeLists.txt（位於模塊的根目錄），用於指示編譯構建native-lib.cpp。

如今看下native-lib.cpp文件內容

#include <jni.h>
#include <string>

extern "C" JNIEXPORT jstring JNICALL
Java_com_cyy_jnidemo_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}
複製代碼

簡單的看出來他就是返回來一個字符串。

再看下CMakeLists.txt文件的內容?

# 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)

# 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.
        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)

# 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

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})
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cmake_minimum_required:生命要求的cmake最低版本。

add_library :建立共享庫（把工程內的cpp文件都建立成共享庫文件，方便經過頭文件來調用） find_package : 找到後面須要庫和頭文件的包 target_link_libraries:把剛剛生成的${PROJECT_NAME}庫和所需的其它庫連接起來.

具體的含義仍是去百度吧。拿出2-3個小時，這地方相信確定就看的懂了。

那看下他在activity中咋用的呢？

就是這麼簡單。。。

如今運行下：

在已有項目中支持C/C++原生代碼

其實很簡單就幾步：

• 咱們也在app模塊下建立個cpp包，而後在這個包下，也新建個native-lib.cpp文件，能夠把以前他自動建立的內容複製進來，也能夠本身寫。

• 而後在app模塊下，也建立個CMakeLists.txt文件。能夠把以前那個CMakeLists.txt內容複製進來，可是路徑記得必定要改爲本身的。

• 最後在app模塊下的build.gradle中添加這兩個：

就ok了。