[英]App crashes when running code from in fragment
我正在 android studio 中制作我的第一個應用程序。 到目前為止,我已經使用片段構建了一個底部導航欄。 我現在正在嘗試向其中一個片段添加日歷功能,我復制了一個使用活動來運行代碼的教程,並認為使用“視圖”存在問題。
這是打開導航欄以打開片段的代碼。
@Override
public boolean onNavigationItemSelected(MenuItem item) {
switch (item.getItemId()){
case R.id.home:
getSupportFragmentManager().beginTransaction().replace(R.id.container,homeFragment).commit();
return true;
case R.id.calendar:
getSupportFragmentManager().beginTransaction().replace(R.id.container,calendarFragment).commit();
return true;
case R.id.wellbeing:
getSupportFragmentManager().beginTransaction().replace(R.id.container,wellbeingFragment).commit();
return true;
}
return false;
這是我的日歷片段中的 java,當從導航欄打開時,應用程序會崩潰
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
initWidgets();
selectedDate = LocalDate.now();
setMonthView();
return inflater.inflate(R.layout.fragment_calendar, container, false);
}
private void initWidgets()
{
calendarRecyclerView = requireView().findViewById(R.id.calendarRecyclerView);
monthYearText = requireView().findViewById(R.id.monthYearTV);
}
private void setMonthView()
{
monthYearText.setText(monthYearFromDate(selectedDate));
ArrayList<String> daysInMonth = daysInMonthArray(selectedDate);
CalendarAdapter calendarAdapter = new CalendarAdapter(daysInMonth, this);
RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getContext(),7);
calendarRecyclerView.setLayoutManager(layoutManager);
calendarRecyclerView.setAdapter(calendarAdapter);
}
這是我在 logcat 中收到的錯誤消息
2022-05-12 12:45:05.305 10950-10950/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 10950
java.lang.IllegalStateException: Fragment CalendarFragment{c4de180} (94b1c782-ca39-403f-b45b-5d0d7a042f15 id=0x7f080087) did not return a View from onCreateView() or this was called before onCreateView().
at androidx.fragment.app.Fragment.requireView(Fragment.java:1964)
at com.example.myapplication.CalendarFragment.initWidgets(CalendarFragment.java:41)
at com.example.myapplication.CalendarFragment.onCreateView(CalendarFragment.java:30)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2963)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2100)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:524)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7842)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
我相信日歷代碼中沒有錯誤,並且與片段代碼中的onCreateView
有關。
在從onCreateView()
返回非空值之前,您不能調用requireView()
) 。
移動這些行
initWidgets();
selectedDate = LocalDate.now();
setMonthView();
(其中initWidgets()
調用 requireView( requireView()
)從onCreateView()
到例如onViewCreated()
。
是的,它崩潰了,因為在返回 inflater 之前沒有從 fragment_calendar 布局調用 findViewById,因此在 return 語句之后調用的任何內容都不會被執行,並將返回 NullPointerException。 除非你重寫 onViewCreated 方法並記下代碼
所以為了避免這種情況,你需要重寫 onViewCreated 方法或者你必須返回視圖。 請記住,如果要返回視圖,則必須在返回視圖語句之前到達所有代碼或公共方法。 否則會因為異常而崩潰
檢查此代碼,它將正確修復
public class TestFragment extends Fragment {
RecyclerView calendarRecyclerView;
TextView monthYearText;
@Nullable
@org.jetbrains.annotations.Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable @org.jetbrains.annotations.Nullable ViewGroup container, @Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
selectedDate = LocalDate.now();
return inflater.inflate(R.layout.fragment_calendar, container, false);
}
@Override
public void onViewCreated(@NonNull View view, @Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
initWidgets(view);
setMonthView();
}
private void initWidgets(View view) {
calendarRecyclerView = view.findViewById(R.id.calendarRecyclerView);
monthYearText = view.findViewById(R.id.monthYearTV);
}
private void setMonthView() {
monthYearText.setText(monthYearFromDate(selectedDate));
ArrayList<String> daysInMonth = daysInMonthArray(selectedDate);
CalendarAdapter calendarAdapter = new CalendarAdapter(daysInMonth, getActivity());
RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getActivity(), 7);
calendarRecyclerView.setLayoutManager(layoutManager);
calendarAdapter.setAdapter(calendarAdapter);
}
}
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