huanghaibin-dev/CalendarView · warning

e.printStackTrace()

Error message

e.printStackTrace()

What it means

MonthViewPager.instantiateItem reflectively constructs the configured month view class. On failure it prints the stack trace and returns a DefaultMonthView as a fallback, so the calendar still renders but the custom month view silently never appears.

Solutions

1. Give the class a public constructor taking Context and keep it lightweight (no casting to Activity).
2. Make the class top-level or static nested and public.
3. Check logcat for the printed exception (NoSuchMethodException, InvocationTargetException, etc.).
4. Add a keep rule for the class and its constructor.
5. If a constructor throws, wrap its body in try/catch or move fragile initialization to onMeasure/onDraw.

Example fix

// before
public CustomMonthView(Context context) {
    super(context);
    ((MyActivity) context).getData(); // throws ClassCastException at instantiation
}
// after
public CustomMonthView(Context context) {
    super(context);
    // defer data access; obtain via listener/setup after construction
}

Class<?> cls = Class.forName("com.example.CustomMonthView");
cls.getConstructor(Context.class); // throws early if reflection will fail at bind time

static boolean instantiableMonthView(Class<?> cls) {
    try {
        return BaseMonthView.class.isAssignableFrom(cls)
            && cls.getConstructor(Context.class) != null;
    } catch (NoSuchMethodException e) { return false; }
}

// The library already falls back to DefaultMonthView; add your own guard:
try {
    Constructor<?> ctor = CustomMonthView.class.getConstructor(Context.class);
    ctor.newInstance(context);
} catch (Throwable t) {
    Log.w("Calendar", "CustomMonthView unavailable, default used", t);
}

When it happens

Trigger: Custom month view class configured via app:calendar_month_view_class lacks a public (Context) constructor, is a non-static inner class, throws in its constructor, or fails newInstance due to access/obfuscation issues.

Common situations: Declaring the custom view as an inner class of an Activity; constructor doing context.cast to Activity and throwing; ProGuard stripping the constructor; class instantiated during RecyclerView binding right after app start.

Related errors

• e.printStackTrace()
• e.printStackTrace()
• e.printStackTrace()
• e.printStackTrace()

AI-assisted analysis of huanghaibin-dev/CalendarView@f5479ea3ba (2026-09-11). Data as JSON: /api/errors/3e43931df20ddbba. Report an issue: GitHub.

Appendix: source

Thrown at calendarview/src/main/java/com/haibin/calendarview/MonthViewPager.java:624

            return isUpdateMonthView ? POSITION_NONE : super.getItemPosition(object);
        }

        @Override
        public boolean isViewFromObject(View view, @NonNull Object object) {
            return view.equals(object);
        }

        @NonNull
        @Override
        public Object instantiateItem(@NonNull ViewGroup container, int position) {
            int year = (position + mDelegate.getMinYearMonth() - 1) / 12 + mDelegate.getMinYear();
            int month = (position + mDelegate.getMinYearMonth() - 1) % 12 + 1;
            BaseMonthView view;
            try {
                Constructor constructor = mDelegate.getMonthViewClass().getConstructor(Context.class);
                view = (BaseMonthView) constructor.newInstance(getContext());
            } catch (Exception e) {
                e.printStackTrace();
                return new DefaultMonthView(getContext());
            }
            view.mMonthViewPager = MonthViewPager.this;
            view.mParentLayout = mParentLayout;
            view.setup(mDelegate);
            view.setTag(position);
            view.initMonthWithDate(year, month);
            view.setSelectedCalendar(mDelegate.mSelectedCalendar);
            container.addView(view);
            return view;
        }

        @Override
        public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
            BaseView view = (BaseView) object;
            view.onDestroy();
            container.removeView(view);
        }

View on GitHub (pinned to f5479ea3ba)