Android studio 使用Cmake完成C/C++ 的使用以及生成so檔案
Android studio 2.2版本以後對C/C++的支援可以說很方便了,當然官方推薦使用Cmake完成對C/C++的支援
2.2版本以上的同學新建一個專案就知道了,步驟如下:
File -> New -> New Project,如下圖:
然後勾選Include C++ support,一直next ,最後Finish以後,專案就出現了,和一般的專案略有不同,其實只要多了幾個檔案,而已:
1:目錄下多了個CmakeLists.txt檔案
2:src目錄下多了一個cpp目錄,裡面有個.cpp檔案,C++檔案都是以.cpp結尾的。
3:就是build.gradle內容中添加了幾行配置
一一解讀一下,先來看看CmakeLists.txt 檔案裡面的內容是什麼:
# 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} )
這裡有設定Cmake版本啊,引用的cpp檔案的路徑啊等等,如果自己引用的話 其實值需要修改引用的cpp路徑即可,
其他的暫時不需要動
看下native_lib.cpp檔案內容:
#include <jni.h> #include <string> extern "C" JNIEXPORT jstring JNICALL Java_com_process_main_myapplication_MainActivity_stringFromJNI( JNIEnv* env, jobject /* this */) { std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str()); }
很簡單 其實就是輸出Hello from C++這段文字:
再看下build.gradle的配置改變:
apply plugin: 'com.android.application'
android {
compileSdkVersion 25
buildToolsVersion "25.0.2"
defaultConfig {
applicationId "com.process.main.myapplication"
minSdkVersion 22
targetSdkVersion 25
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags ""
}
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:25.1.1'
compile 'com.android.support.constraint:constraint-layout:1.0.0-beta4'
testCompile 'junit:junit:4.12'
}
主要多了兩個地方的改變:
1:defaultConfig中新增:
externalNativeBuild {
cmake {
cppFlags ""
}
}
2:在android{}中新增:
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
其實也就是引用CmakeLists.txt檔案。
說到這裡,大致知道C++專案的大致結構了。那麼原始專案怎麼新增C++呢,步驟如下:
1,現在src/main目錄下新建cpp目錄和java目錄同級,然後在cpp目錄中新建一個.cpp檔案,這裡以native-lib.cpp為例子直接copy進去
2,右鍵專案(選中專案,然後右鍵)如下:
選擇第二個Link C++ Project with Gradle,出現以下介面:
關於Project Path是選擇CmakeLists.txt檔案的路徑,這裡先把之前的CmakeLists.txt檔案直接copy過來,然後相應的修改即可:
選擇CmakeLists檔案然後點選OK按鈕。修改CmakeLists.txt檔案中的cpp檔案引用目錄即可(add_library {第三行})。
接下來,在java程式碼中呼叫C++程式碼啦,看下MainActivity中的程式碼:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Example of a call to a native method
TextView tv = (TextView) findViewById(R.id.sample_text);
tv.setText(stringFromJNI());
}
/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native String stringFromJNI();
// Used to load the 'native-lib' library on application startup.
static {
System.loadLibrary("native-lib");
}
}
這裡注意System.loadLibrary("native-lib"),載入(native-lib)Library,這裡是CmakeLists檔案中配置好的Library名字要對應。
然後就是native呼叫stringFromJNI ()方法啦》
最後編譯一下app,Make Project build一下,然後run到手機上就可以運行了。
這裡有同學想問那.so檔案在哪裡找啊 ,如下圖:
這裡的so檔案就可以用到其他專案中啦;
至此一個簡單的使用C++專案就完成啦