在 fragment 之间传递字符串时出现 java.lang.NullPointerException

Question

我有两个 fragment ScanFragment.java 和 ProductViewFragment.java 我想将字符串 pid 的值从 ScanFragment 传递到 ProductViewFragment。但是，我得到了 java.lang.NullPointerException。

1) ScanFragment.java

PreviewCallback previewCb = new PreviewCallback() {
        public void onPreviewFrame(byte[] data, Camera camera) {
            Parameters parameters = camera.getParameters();
            Size size = parameters.getPreviewSize();

            Image barcode = new Image(size.width, size.height, "Y800");
            barcode.setData(data);

            int result = scanner.scanImage(barcode);

            if (result != 0) {
                previewing = false;
                mCamera.setPreviewCallback(null);
                mCamera.stopPreview();

                SymbolSet syms = scanner.getResults();
                for (Symbol sym : syms) {
                    scanText.setText(/**"barcode result " + **/sym.getData());
                    barcodeScanned = true;
                }
                String pid = ((TextView) getView().findViewById(R.id.scanText)).getText()
                        .toString();

                Bundle bundle = new Bundle();
                bundle.putString("pid", pid);

                ProductViewFragment fragment = new ProductViewFragment();
                fragment.setArguments(bundle);

                FragmentTransaction mFragmentTransaction = getFragmentManager().beginTransaction();
                mFragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE); 
                mFragmentTransaction.replace(R.id.frame_container, new ProductViewFragment(), "Product view");
                mFragmentTransaction.addToBackStack(null);
                mFragmentTransaction.commit();
            }
        }
    };

2) ProductViewFragment.java

public class ProductViewFragment extends Fragment {

public ProductViewFragment(){}

TextView txtName;
TextView txtPrice;
TextView txtDesc;
TextView productErrorMsg;
EditText editTextQuantity;
ImageView image;
Button btnAddtocart;
Button btnCancel;
public static String pid;

// JSON parser class
JSONParser1 jsonParser = new JSONParser1();

// single product url
private static final String url_product_details = "http://www.zulanawi.com/learn2crack_login_api/";

// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCT = "product";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
private static final String TAG_PRICE = "price";
private static final String TAG_DESCRIPTION = "description";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_product, container, false);
    // Loader image - will be shown before loading image
    int loader = R.drawable.loader;
    // save button
    btnAddtocart = (Button) rootView.findViewById(R.id.btnAddtocart);
    btnCancel = (Button) rootView.findViewById(R.id.btnCancel);
    productErrorMsg = (TextView) rootView.findViewById(R.id.product_error);
    // Imageview to show
    image = (ImageView) rootView.findViewById(R.id.image);

    // getting product details from intent
    //Intent i = getIntent();

    // getting product id (pid) from intent
    //pid = getActivity().getIntent().getStringExtra(TAG_PID);

    //Bundle bundle = this.getArguments();
    pid = getArguments().getString("pid");

    // Image url
    String image_url = "http://xxx.xxx.com/upload/products/" + pid +".jpg";

    // ImageLoader class instance
    ImageLoader imgLoader = new ImageLoader(getActivity().getApplicationContext());

    // whenever you want to load an image from url
    // call DisplayImage function
    // url - image url to load
    // loader - loader image, will be displayed before getting image
    // image - ImageView 
    imgLoader.DisplayImage(image_url, loader, image);


    // Getting complete product details in background thread
    //new NetCheck().execute();
    new GetProductDetails().execute();

    // Add to cart button click event
    btnAddtocart.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // starting background task to update product
            //new SaveProductDetails().execute();

            //Get Global Controller Class object (see application tag in AndroidManifest.xml)
            //Product arraylist size
            //Intent addToCart = new Intent(getActivity().getApplicationContext(), ScreenFirstFragment.class);
            //startActivity(addToCart);
            FragmentTransaction mFragmentTransaction = getFragmentManager().beginTransaction();
            mFragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE); 
            mFragmentTransaction.replace(R.id.frame_container, new ScreenFirstFragment(), "First Screen");
            mFragmentTransaction.commit();

        }
    });

3)

The log. 03-31 15:46:36.230: E/AndroidRuntime(6971):    at info.androidhive.slidingmenu.ProductViewFragment.onCreateView(ProductViewFragment.java:99) is pid = getArguments().getString("pid"); at ProductViewFragment

    03-31 15:45:57.735: E/(6971): Device driver API match
    03-31 15:45:57.735: E/(6971): Device driver API version: 17
    03-31 15:45:57.735: E/(6971): User space API version: 17 
    03-31 15:45:57.755: E/(6971): mali: REVISION=Linux-r3p1-01rel1 BUILD_DATE=Tue Jul  2 15:06:24 KST 2013 
    03-31 15:46:36.230: E/AndroidRuntime(6971): FATAL EXCEPTION: main
    03-31 15:46:36.230: E/AndroidRuntime(6971): java.lang.NullPointerException
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at   info.androidhive.slidingmenu.ProductViewFragment.onCreateView(ProductViewFragment.java:99)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at   android.app.Fragment.performCreateView(Fragment.java:1695)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:903)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.BackStackRecord.run(BackStackRecord.java:682)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.os.Handler.handleCallback(Handler.java:725)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.os.Handler.dispatchMessage(Handler.java:92)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.os.Looper.loop(Looper.java:137)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at android.app.ActivityThread.main(ActivityThread.java:5279)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at java.lang.reflect.Method.invokeNative(Native Method)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at java.lang.reflect.Method.invoke(Method.java:511)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
    03-31 15:46:36.230: E/AndroidRuntime(6971):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

使用

mFragmentTransaction.replace(R.id.frame_container,fragment, "Product view");

传递您正在调用 setArguments 的 ProductViewFragment 实例，而不是通过 new ProductViewFragment() 传递新实例。