片段中AsyncTask中的ProgressDialog崩溃

Question

我在Activity有一个带有AsyncTask的Fragment 。 但是在运行搜索时出现此异常：

Attempt to invoke virtual method 'android.content.res.Resources$Theme android.content.Context.getTheme()' on a null object reference.

它与Fragment不知道Activity是否正在运行有关，但是我不知道如何解决它。 请帮忙。 这是代码：

class Send_API extends AsyncTask<String, Void, String> {

        private ProgressDialog dialog;

        @Override
        protected void onPreExecute() {
            if (movieList != null){
                movieList.clear();
                adapter.notifyDataSetChanged();
            }

            dialog = new ProgressDialog(getActivity());
            dialog.setMessage("Searching...");
            dialog.show();
        }

        @Override
        protected String doInBackground(String... params) {
            String queryString = null;
            try {
                queryString = "" +
                        "s=" + URLEncoder.encode(txt, "utf-8");
            } catch (UnsupportedEncodingException e) {
            }
            return HttpHandler.get(params[0], queryString);
        }


        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            dialog.dismiss();
            if (result == null) {
                Toast.makeText(getActivity(), "error getting results...", Toast.LENGTH_LONG).show();

            } else {

                try {
                    JSONObject json = new JSONObject(result);

                    JSONArray searchArray = json.getJSONArray("Search");

                    for (int i = 0; i < searchArray.length(); i++) {
                        JSONObject searchObject = searchArray.getJSONObject(i);
                        String title = searchObject.getString("Title");
                        String type = searchObject.getString("Type");
                        String year = searchObject.getString("Year");
                        String imdbID = searchObject.getString("imdbID");
                        String poster_url = searchObject.getString("Poster");
                        movieList.add(new Movie(title, type, year, imdbID, poster_url));

                        Log.e(TAG, "MovieList is " + movieList);


                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                    Toast.makeText(getActivity(), "error parsing results...", Toast.LENGTH_LONG).show();
                }

                adapter.notifyDataSetChanged();

            }
        }

    }

Answer 1

  dialog = new ProgressDialog(getActivity());

初始化Fragment时， getActivity()将返回null。 您必须等到片段生命周期中的onAttach() ，它才能返回非null值。

这就是NPE的原因。

总体而言，片段中不要包含非默认构造函数。 仅在onCreateView()设置片段视图。

Answer 2

尝试将基本上下文传递给您的asynctask，并用它或getApplicationContext()替换getActivity() getApplicationContext()