访问列表视图时应用程序不断崩溃

Question

在我的应用中，我在列表视图中显示数据。滚动浏览列表视图时，我的应用程序崩溃了。我应该做出哪些改变？

正如错误中给出的，我的 RecipeListFragment.java 文件是：

public class RecipeListFragment extends Fragment {
MyDatabase db;
boolean isfav = false;
Context context;
ListView lvrecipe;

ArrayList<RecipePojo> recipelist = new ArrayList<RecipePojo>();  
LinearLayout ll;
DisplayImageOptions options;
private ProgressDialog progress;
int position;
String recipeid;
int checkcounter = 0;

private Custom_Adapter adapter;

public RecipeListFragment() {

}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.activity_recipe_list_actvity, container, false);
    context = getActivity();

    lvrecipe = (ListView) rootView.findViewById(R.id.lvrecipe);
    //  adView = (MoPubView)rootView. findViewById(R.id.mopub_sample_ad);

    new getrecipe().execute();


    db = new MyDatabase(getActivity());


    //  recipelist = DataManager.recipelist;
    position = DataManager.selectedposition;
    adapter = new Custom_Adapter(getActivity());
    adapter.notifyDataSetChanged();
    lvrecipe.setAdapter(adapter);

    /*  if(recipeid!=null){
        checkcounter = db.checkrecipefav(recipeid);
        }


    if (checkcounter > 0) {
        isfav = true;
    } else {
        isfav = false;
    }

    db.close();*/


    lvrecipe.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            DataManager.selectedposition = position;
            Intent i = new Intent(getActivity(), RecipeDescription.class);
            i.putExtra("cusinename", DataManager.cusinename);
            startActivity(i);
            getActivity().finish();
        }
    });

    //  adddisplay();

    return rootView;
}

@Override
public void onResume() {
    super.onResume();
}


public class Custom_Adapter extends BaseAdapter {

    private LayoutInflater mInflater;

    public Custom_Adapter(Context c) {
        mInflater = LayoutInflater.from(c);
    }

    @Override
    public int getCount() {
        if (recipelist != null) {
            return recipelist.size();
        } else {
            return 0;
        }
    }

    @Override
    public Object getItem(int position) {
        if (recipelist != null) {
            return recipelist.get(position);
        } else {
            return 0;
        }
    }

    @Override
    public long getItemId(int position) {
        if (recipelist != null) {
            return position;
        } else {
            return 0;
        }
    }

    @SuppressWarnings("deprecation")
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.recipelist, null);
            holder = new ViewHolder();

            holder.txttile = (TextView) convertView.findViewById(R.id.txttile);
            holder.imgrecipe = (ImageView) convertView.findViewById(R.id.imgrecipe);
            holder.fav_unfav = (ImageView) convertView.findViewById(R.id.fav_unfav);
            holder.ratingbar = (RatingBar) convertView.findViewById(R.id.ratingbar);
            holder.txtduration = (TextView) convertView.findViewById(R.id.txtduration);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }


        if (recipelist != null) {
            recipeid = recipelist.get(position).getRecipeid();
            checkcounter = db.checkrecipefav(recipeid);
        }

        if (checkcounter > 0) {
            isfav = true;
        } else {
            isfav = false;
        }

        db.close();

        if (isfav) {
            holder.fav_unfav.setImageResource(R.drawable.favourite);
        } else {
            holder.fav_unfav.setImageResource(R.drawable.favourites);
        }

        Typeface face1 = Typeface.createFromAsset(getActivity().getAssets(), "sinkin_sans_300_light.ttf");
        Typeface face2 = Typeface.createFromAsset(getActivity().getAssets(), "sinkin_sans_400_regular.ttf");

        holder.txttile.setTypeface(face2);
        holder.txtduration.setTypeface(face1);


        holder.txttile.setText(recipelist.get(position).getRecipename());

        try {
            String[] prep = recipelist.get(position).getPrep_time().split(" ");
            String[] cook = recipelist.get(position).getCooking_time().split(" ");

            int totalTime = Integer.parseInt(prep[0]) + Integer.parseInt(cook[0]);

            holder.txtduration.setText(""+totalTime+" min");

        } catch (NumberFormatException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }


        String url = DataManager.photourl + "recipe/" + recipelist.get(position).getRecipeid() + ".jpg";

        try {
            url = URLDecoder.decode(url, "UTF-8");
            url = url.replaceAll(" ", "%20");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }


        if (recipelist.get(position).getVideo_link().equals("none")) {
            //  holder.imgvideo.setVisibility(View.GONE);
        }

        String rating = recipelist.get(position).getRatings();

        if (rating != null && rating.trim().length() > 0) {
            holder.ratingbar.setRating(Float.valueOf(rating));
        }

        //holder.imgrecipe.setImage(url,getResources().getDrawable(R.drawable.cusine));


        if (holder.imgrecipe != null) {

            if (url != null && url.trim().length() > 0) {
                //final ProgressBar pbar = holder.pbar;
                final ImageView imageView = holder.imgrecipe;
                //final RelativeLayout imgRL = holder.imageRL;

                ImageLoader.getInstance().displayImage(url, holder.imgrecipe, options, new SimpleImageLoadingListener() {
                    @Override
                    public void onLoadingComplete(String imageUri,
                                                  View view, Bitmap loadedImage) {
                        super.onLoadingComplete(imageUri, view, loadedImage);
                        imageView.setAdjustViewBounds(true);
                    }

                    @Override
                    public void onLoadingFailed(String imageUri, View view, FailReason failReason) {
                        super.onLoadingFailed(imageUri, view, failReason);
                    }

                    @Override
                    public void onLoadingStarted(String imageUri, View view) {
                        super.onLoadingStarted(imageUri, view);
                    }
                });

            } else {
            }

        }


        return convertView;
    }

    class ViewHolder {
        TextView txttile, txtduration;
        ImageView imgrecipe;
        ImageView fav_unfav;
        RatingBar ratingbar;
    }
}

public class getrecipe extends AsyncTask<String, Void, String> {
    boolean response = false;

    @Override
    protected void onPreExecute() {
        //progress = ProgressDialog.show(context, "Getting Data...","Please wait....");

        progress = new ProgressDialog(getActivity());
        progress.setMessage("Please wait....");
        progress.show();
    }

    @Override
    protected String doInBackground(String... params) {
        response = APIManager.getrecipebycusine(DataManager.CUISINE_ID);

        return "";
    }

    @Override
    protected void onPostExecute(String result) {

        progress.cancel();
        if (response) {

            if (DataManager.status.equalsIgnoreCase("1")) {
                recipelist = DataManager.recipelist;
                adapter.notifyDataSetChanged();
                //Intent i = new Intent(getActivity(),RecipeListActvity.class);

                //startActivity(i);

            } else {

                connectionerror();

            }
        } else {

            connectionerror();
        }

    }

    @Override
    protected void onProgressUpdate(Void... values) {

    }
}

public void alert() {
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(getActivity());

    alertDialog.setTitle("No Recipe!");

    alertDialog.setMessage("No Recipe for this Cusine");

    alertDialog.setPositiveButton("OK",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {

                }
            });

    alertDialog.show();
}

private static class AnimateFirstDisplayListener extends SimpleImageLoadingListener {

    static final List<String> displayedImages = Collections.synchronizedList(new LinkedList<String>());

    @Override
    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
        if (loadedImage != null) {
            ImageView imageView = (ImageView) view;
            boolean firstDisplay = !displayedImages.contains(imageUri);
            if (firstDisplay) {
                FadeInBitmapDisplayer.animate(imageView, 500);
                displayedImages.add(imageUri);
            }
        }
    }
}

public void connectionerror() {
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(getActivity());

    alertDialog.setTitle("Error!");

    alertDialog.setMessage("Connection Lost ! Try Again");

    alertDialog.setPositiveButton("Retry",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {

                    new getrecipe().execute();

                }
            });

    alertDialog.show();
}}

Crashlytics 中显示的错误是：

   Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources$Theme android.content.Context.getTheme()' on a null object reference
   at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:154)
   at android.app.AlertDialog$Builder.<init>(AlertDialog.java:379)
   at com.raccoonfinger.salad.RecipeListFragment.connectionerror(RecipeListFragment.java:381)
   at com.raccoonfinger.salad.RecipeListFragment$getrecipe.onPostExecute(RecipeListFragment.java:335)
   at com.raccoonfinger.salad.RecipeListFragment$getrecipe.onPostExecute(RecipeListFragment.java:296)
   at android.os.AsyncTask.finish(AsyncTask.java:632)
   at android.os.AsyncTask.access$600(AsyncTask.java:177)
   at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
   at android.os.Handler.dispatchMessage(Handler.java:102)
   at android.os.Looper.loop(Looper.java:135)
   at android.app.ActivityThread.main(ActivityThread.java:5312)
   at java.lang.reflect.Method.invoke(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:372)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

Answer 1

请不要在Fragment 中直接使用getActivity()，因为有时它会返回null..

始终将activity 作为构造函数中的参数传递..!!

请使用以下方法创建您的Fragment 并使用activity 引用而不是getActivity()..

public static AboutFragment newInstance(Activity activity) {
        AboutFragment aboutFragment = new AboutFragment();
        aboutFragment.mActivity = activity;
        return aboutFragment;
    }

希望它会有所帮助。

谢谢..!!