and cmake 链接库及播放例子 及读文件

建一个Native-cpp工程

1、引入android库的方法

CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)

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 )

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 )
find_library( # Sets the name of the path variable.
        android-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        android )

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib}   ${android-lib})

2、java

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
    }
    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();

    public native void playRgb(Surface sf);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));
        /*
        setContentView(R.layout.activity_main);

        // Example of a call to a native method
        TextView tv = findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
        */
    }

    //------------------------------>
    //视图内部类
    class MyView extends SurfaceView implements SurfaceHolder.Callback
    {
        private SurfaceHolder holder;
        private MyThread myThread;
        public MyView(Context context) {
            super(context);
            // TODO Auto-generated constructor stub
            holder = this.getHolder();
            holder.addCallback(this);
            myThread = new MyThread(holder);//创建一个绘图线程
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width,
                                   int height) {
            // TODO Auto-generated method stub

        }

        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            // TODO Auto-generated method stub
            myThread.isRun = true;
            myThread.start();
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            // TODO Auto-generated method stub
            myThread.isRun = false;
        }

    }
    //线程内部类
    class MyThread extends Thread
    {
        private SurfaceHolder holder;
        public boolean isRun ;
        public  MyThread(SurfaceHolder holder)
        {
            this.holder =holder;
            isRun = true;
        }
        @Override
        public void run()
        {
            int count = 0;
            while(isRun)
            {
                Canvas c = null;
                try
                {
                    synchronized (holder)
                    {
                        //new Hello().playRgb();
                        playRgb(holder.getSurface());

                        Thread.sleep(1000);//睡眠时间为1秒
                    }
                }
                catch (Exception e) {
                    // TODO: handle exception
                    e.printStackTrace();
                }
                finally
                {
                    if(c!= null)
                    {
                        holder.unlockCanvasAndPost(c);//结束锁定画图，并提交改变。

                    }
                }
            }
        }
    }

}

3、cpp  看来该有的头文件和库都有了

#include <jni.h>
#include <string>
#include <unistd.h>
#include <android/native_window_jni.h>
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_testnativecpp_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}
char rgb[640*480*4];
extern "C" JNIEXPORT void JNICALL
Java_com_example_testnativecpp_MainActivity_playRgb(
        JNIEnv* env,
        jobject /* this */,
        jobject surface) {

    int outWidth = 640;
    int outHeight = 480;
    //char *rgb =  (char* )malloc(outWidth * outHeight * 4);
    ANativeWindow *nwin = ANativeWindow_fromSurface(env, surface);
    ANativeWindow_setBuffersGeometry(nwin, outWidth, outHeight, WINDOW_FORMAT_RGBA_8888);

    for(int i=0;i<255;i++){
        memset(rgb,i,640*480);
        memset(rgb+640*480,255-i,640*480);

        ANativeWindow_Buffer wbuf;
        ANativeWindow_lock(nwin, &wbuf, 0);
        uint8_t *dst = (uint8_t *) wbuf.bits;
        memcpy(dst, rgb, outWidth * outHeight * 4);
        ANativeWindow_unlockAndPost(nwin);
        usleep(100);
    }
}

试试读文件竟然直接可以

char StrLine[1024]={0};
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_testnativecpp_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    FILE *fp;
    char ch;
    char *strFile = "data/data/com.example.testnativecpp/1.txt";
    if((fp=fopen(strFile,"r"))==NULL){
       // printf("
Cannot open file strike any key exit!");

        return env->NewStringUTF("wrong!");
    }
    fgets(StrLine,1023,fp);
    fclose(fp);
    return env->NewStringUTF(StrLine);
}