Java OpenCV：关于Sobel衍生变量的教程；无法在Android上工作，nullpointerexception

我试图将这个C/C++代码翻译成Java for Android。 不幸的是，它不起作用

我的代码：`公共类MainActivity扩展活动{

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main); 
}

private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
    @Override
    public void onManagerConnected(int status) {
        if (status == LoaderCallbackInterface.SUCCESS ) {
            // now we can call opencv code !
            try {
                krawedz();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Log.e("moje", "brak obrazka");
                e.printStackTrace();
            }
        } else {
            super.onManagerConnected(status);
        }
    }
};

@Override
public void onResume() {
    super.onResume();
    OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_5,this, mLoaderCallback);
}

public void krawedz() throws IOException{
    Mat src, src_gray = null;
    Mat grad_x = null, grad_y = null;
    Mat abs_grad_x = null, abs_grad_y = null;
    Mat grad = null;
    int skala = 1;
    int delta = 0;
    int depth = 3; //CV16_S

    //załaduj obrazek
    src = Utils.loadResource(this, R.drawable.obraz);
    if(src.empty()){
        Log.e("moje", "brak obrazka");
    }
    //na szaro

    Imgproc.GaussianBlur(src, src_gray, new org.opencv.core.Size(3,3), 0, 0);
    Imgproc.cvtColor(src, src_gray, 7 ); //7=CV_RGB2GRAY

    //Gradient x
    //Imgproc.Scharr(src_gray, grad_x, depth, 1, 0, skala, delta, Imgproc.BORDER_DEFAULT);
    Imgproc.Sobel(src_gray, grad_x, depth, 1, 0, 3, skala, delta, Imgproc.BORDER_DEFAULT);
    Core.convertScaleAbs(grad_x, abs_grad_x);

    //Gradient Y
    //Imgproc.Scharr(src_gray, grad_y, depth, 0, 1, skala, delta, Imgproc.BORDER_DEFAULT);
    Imgproc.Sobel(src_gray, grad_y, depth, 0, 1, 3, skala, delta, Imgproc.BORDER_DEFAULT);
    Core.convertScaleAbs(grad_y, abs_grad_y);

    Core.addWeighted(abs_grad_x, 0.5, abs_grad_y, 0.5, 0, grad);

    // zamiana macierzy na bitmape:
    Bitmap bm = Bitmap.createBitmap(grad.cols(), grad.rows(),Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(grad, bm);

    // rysowanie bitmapy
    ImageView iv = (ImageView) findViewById(R.id.imageView1);
    iv.setImageBitmap(bm);
}

}`

LogCat对此代码的看法：

    03-14 16:45:52.944: E/AndroidRuntime(25349): FATAL EXCEPTION: main
03-14 16:45:52.944: E/AndroidRuntime(25349): Process: com.example.wykrywanie_krawedzi, PID: 25349
03-14 16:45:52.944: E/AndroidRuntime(25349): java.lang.NullPointerException
03-14 16:45:52.944: E/AndroidRuntime(25349):    at org.opencv.imgproc.Imgproc.GaussianBlur(Imgproc.java:533)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at com.example.wykrywanie_krawedzi.MainActivity.krawedz(MainActivity.java:73)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at com.example.wykrywanie_krawedzi.MainActivity$1.onManagerConnected(MainActivity.java:38)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at org.opencv.android.AsyncServiceHelper$1.onServiceConnected(AsyncServiceHelper.java:318)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1110)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1127)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.os.Handler.handleCallback(Handler.java:733)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.os.Handler.dispatchMessage(Handler.java:95)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.os.Looper.loop(Looper.java:136)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at android.app.ActivityThread.main(ActivityThread.java:5086)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at java.lang.reflect.Method.invokeNative(Native Method)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at java.lang.reflect.Method.invoke(Method.java:515)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
03-14 16:45:52.944: E/AndroidRuntime(25349):    at dalvik.system.NativeStart.main(Native Method)

替换

grad_x = null, grad_y = null, abs_grad_x = null, abs_grad_y = null, grad = null 

借

---

还必须初始化src_gray（这是日志文件中出现空指针异常的原因）：src_gray=new Mat（）；

grad_x = new Mat(), grad_y = new Mat(), abs_grad_x = new Mat(), abs_grad_y = new Mat(), grad = new Mat();