我有一个名为 CBT_practice 的活动，其中包含以下片段： objective_fragment ， subjective_fragment 和 theory_fragment 。这些片段通过viewpager动态添加到活动中。
但是将Objective_fragment添加到viewpager之后，我遇到了问题。父活动（CBT_practice）使用LoaderManager进行sqlite db查询以检索问题列表，然后这些片段在其onCreateView生命周期中被片段访问，然后存储在变量中。
但是，只有在我最小化并还原了电话屏幕（即，活动被暂停然后恢复）之后，我才尝试从父活动（CBT_practice）中调用Objective_fragment（getScore()）中的方法单击按钮后，我收到一条错误消息，指出列表的大小为0。当我不最小化并恢复活动时，不会发生这种情况
列表是派生的 来自父活动并通过
OnCreateView方法分配暂停并恢复活动后， listSize 以
OnCreateView方法返回60，而以getScore()方法返回0
令人惊讶的是，列表存储在全局变量中，然后通过onCreateView方法进行分配
这里是Parent活动加载器回调，它从db获取问题列表：
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
progressBarLN.setVisibility(View.GONE);
data.moveToFirst();
while(!data.isAfterLast()){
id = data.getString(data.getColumnIndex("_id"));
topic_id_selected = data.getString(data.getColumnIndex("topic_id"));
year_id_selected = data.getString(data.getColumnIndex("year_id"));
ques_num = data.getString(data.getColumnIndex("question_num"));
ques = data.getString(data.getColumnIndex("question"));
ans = data.getString(data.getColumnIndex("answer"));
ans_desc = data.getString(data.getColumnIndex("answer_desc"));
opt_ans_id = data.getString(data.getColumnIndex("option_answer_id"));
opt_1 = data.getString(data.getColumnIndex("option_A"));
opt_2 = data.getString(data.getColumnIndex("option_B"));
opt_3 = data.getString(data.getColumnIndex("option_C"));
opt_4 = data.getString(data.getColumnIndex("option_D"));
opt_5 = data.getString(data.getColumnIndex("option_E"));
ques_type_id = data.getString(data.getColumnIndex("question_type_id"));
selected_ans_id = data.getString(data.getColumnIndex("selected_answer_id"));
QuestionAnswerList ques_item = new QuestionAnswerList(ques_num, ques, ans, ans_desc, opt_ans_id, opt_1, opt_2, opt_3,
opt_4, opt_5, ques_type_id, selected_ans_id, topic_id_selected, year_id_selected);
topic_name = get_topic_name(topic_id_selected);
ques_item.set_topic_name(topic_name);
if(ques_item.opt_1!=null && ques_item.opt_2!=null && ques_item.opt_3!=null)
ques_item.setOptions(isShuffleOpt);
ques_ans_list.add(ques_item);
//ques_ans_list contains the list of questions retrieved from the db
data.moveToNext();
}
if(isShuffleQues) Collections.shuffle(ques_ans_list);
viewPager = (ViewPager)findViewById(R.id.viewpager);
//viewPager.setOffscreenPageLimit(ques_type_count);
setUpViewPager(viewPager, ques_type);
tabLayout = (TabLayout)findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
}
这是父活动中的代码，该事件在单击按钮后调用getScore（）方法
//get the objective_fragment
Fragment fragment = adapter.getItem(0);
//calls the getScore() method
((obj_fragment) fragment).getScore();
这是片段的OnCreateView
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
setHasOptionsMenu(true);
View view = inflater.inflate(R.layout.fragment_obj_tv, container, false);
preferences = this.getActivity().getSharedPreferences("pref", Context.MODE_PRIVATE);
quesNoTV = (TextView) view.findViewById(R.id.quesNoTV);
webView = (TextView) view.findViewById(R.id.webview);
rad1 = (RadioButton) view.findViewById(R.id.opt1);
rad2 = (RadioButton) view.findViewById(R.id.opt2);
rad3 = (RadioButton) view.findViewById(R.id.opt3);
rad4 = (RadioButton) view.findViewById(R.id.opt4);
rad5 = (RadioButton) view.findViewById(R.id.opt5);
radGrp = (RadioGroup) view.findViewById(R.id.radiogroup);
rad1.setOnClickListener(radClickListener);
rad2.setOnClickListener(radClickListener);
rad3.setOnClickListener(radClickListener);
rad4.setOnClickListener(radClickListener);
rad5.setOnClickListener(radClickListener);
submit = (Button) view.findViewById(R.id.submit);
next.setOnClickListener(clickListener);
previous = (Button) view.findViewById(R.id.previous);
previous.setOnClickListener(clickListener);
//getting the parent activity
activity = (CBT_Practice) getActivity();
//assigning the list from the parent activity to the fragment ques_list variable
ques_list = activity.ques_ans_list;
//listSize here is 60
listSize = ques_list.size();
ques_obj = ques_list.get(startIndex);
show_question(ques_obj);
return view;
}
这是片段的getScore()方法
public int getScore(){
Intent intent;
Bundle args = new Bundle();
ArrayList<QuestionAnswerList> casted_list = new ArrayList<>(ques_list);
int correct = 0;
for(QuestionAnswerList item : ques_list){
if(item.getPicked_ans_id()==item.get_shuffle_ans_id()&&item.getPicked_ans_id()!=-1) correct = correct+1;
}
int num = correct;
correct = (correct*100)/listSize;
//listSize here is 0
if(activity.ques_type.get(0).equals("0")) {
intent = new Intent(getActivity(), ResultActivity.class);
args.putInt("score", correct);
args.putInt("numOfQues", objective_list.size());
args.putInt("correct", num);
}
else
intent = new Intent(getActivity(), Answers.class);
args.putStringArrayList("types", new ArrayList<>(activity.ques_type));
args.putParcelableArrayList("list", casted_list);
intent.putExtras(args);
getActivity().startActivity(intent);
return correct;
}
我也有这个精确代码的副本，可以正常工作，但是由于我将Firebase添加到了项目中，所以我一直遇到错误。我不知道Firebase依赖项是否会导致错误。我也尝试过使用saveInstance状态并实现了某些活动生命周期，但无济于事