Abstract
本文介紹如何在現(xiàn)有Android studio工程中添加C/C++代碼以及相關(guān)native方法抱婉,并編譯成.so庫科汗。開發(fā)環(huán)境Android Studio 3.x脐嫂,請確認(rèn)已正確安裝NDK晃酒,LLDB,CMake(Tools-SDK Manager-SDK Tools)隙咸。ps:如果是新建項(xiàng)目沐悦,new project時(shí)直接勾選Include c++ support即可。
Step1 添加C/C++代碼
project視圖下五督,定位到app/src/main藏否,右鍵main - New - Directory,命名為cpp充包,在cpp目錄下新建include目錄副签,并添加以下c/c++代碼(注意目錄結(jié)構(gòu))。如圖
c_test.h
#ifndef NDKDEMO_C_TEST_H
#define NDKDEMO_C_TEST_H
const char * cFunction();
#endif
c_test.c
#include "stdio.h"
const char * cFunction(){
const char * str = "String from C !";
return str;
}
cpp_test.h
#ifndef NDKDEMO_CPP_TEST_H
#define NDKDEMO_CPP_TEST_H
const char * cppFunction();
#endif
cpp_test.cpp
#include <iostream>
using namespace std;
const char * cppFunction(){
const char * str = "String from C++ !";
return str;
}
Step2 添加CMakeLists.txt文件
右鍵app/ - New - File误证,命名為CMakeLists.txt继薛,添加內(nèi)容如下(參見注釋)
CMakeLists.txt
cmake_minimum_required(VERSION 3.4.1)
#設(shè)置生成的so動態(tài)庫最后輸出的路徑
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/libs/${ANDROID_ABI})
#.h文件目錄
include_directories(
${CMAKE_SOURCE_DIR}/src/main/cpp/include #h文件目錄
)
add_library( # Sets the name of the library.
ndkdemo-lib #c/cpp代碼將要編譯成為so庫的名稱,java代碼加載庫文件要用這個(gè)名稱
SHARED #動態(tài)庫
src/main/cpp/c_test.c #cpp代碼文件路徑 可以在下面接著隨意添加c愈捅、c++文件
src/main/cpp/cpp_test.cpp
src/main/jni/ndkdemo-lib.c #參見step 5
src/main/jni/ndkdemo-lib.cpp #參見step 5
)
find_library( #調(diào)用系統(tǒng)庫
log-lib #打印用
log )
target_link_libraries( # Specifies the target library.
ndkdemo-lib
${log-lib} )
Step3 Link C++ Project with Gradle
切換到Android視圖,右鍵app慈鸠,選擇" Link C++ Project with Gradle"
設(shè)置step2中新建的CMakeLists.txt的路徑
Step4 添加java代碼
在MainActivity中蓝谨,System.loadLibrary()加載so庫,并添加相關(guān)native方法青团,代碼如下:
public class MainActivity extends AppCompatActivity {
private TextView ctxt;
private TextView cpptxt;
static {
System.loadLibrary("ndkdemo-lib");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ctxt = findViewById(R.id.ctxt);
ctxt.setText(stringFromC());
cpptxt = findViewById(R.id.cpptxt);
cpptxt.setText(stringFromCpp());
}
public static native String stringFromC();
public static native String stringFromCpp();
}
布局文件(activity_main.xml)如下:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="@+id/ctxt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
<TextView
android:id="@+id/cpptxt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
Step5 添加JNI層代碼
光標(biāo)定位到MainActivity中的public static native String stringFromC()譬巫,Alt+Enter后AS會自動新建ndkdemo-lib.c文件和相關(guān)函數(shù)頭,在ndkdemo-lib.c添加以下代碼:
#include <jni.h>
#include "c_test.h"
JNIEXPORT jstring JNICALL
Java_com_example_chaoyc_ndkdemo_MainActivity_stringFromC(JNIEnv *env, jclass type)
{
const char * cStr = cFunction();
return (*env)->NewStringUTF(env, cStr);
}
注:C++代碼調(diào)用的不同
在step5路徑(即app/src/main/jni/)新建ndkdemo-lib.cpp文件督笆,添加代碼如下:
#include <jni.h>
#include "cpp_test.h"
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_chaoyc_ndkdemo_MainActivity_stringFromCpp(
JNIEnv *env,
jclass type)
{
const char * cppStr = cppFunction();
return env->NewStringUTF(cppStr);
}
Step6 查看運(yùn)行結(jié)果和編譯生成的.so庫
運(yùn)行結(jié)果如下:
根據(jù)CMakeLists.txt中指定的路徑芦昔,生成的.so庫如下:
Ref
https://developer.android.google.cn/studio/projects/add-native-code
注
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