{"record":{"id":"3e43931df20ddbba","repo":"huanghaibin-dev/CalendarView","slug":"e-printstacktrace-3e4393","errorCode":null,"errorMessage":"e.printStackTrace()","messagePattern":"e\\.printStackTrace\\(\\)","errorType":"console","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"calendarview/src/main/java/com/haibin/calendarview/MonthViewPager.java","lineNumber":624,"sourceCode":"            return isUpdateMonthView ? POSITION_NONE : super.getItemPosition(object);\n        }\n\n        @Override\n        public boolean isViewFromObject(View view, @NonNull Object object) {\n            return view.equals(object);\n        }\n\n        @NonNull\n        @Override\n        public Object instantiateItem(@NonNull ViewGroup container, int position) {\n            int year = (position + mDelegate.getMinYearMonth() - 1) / 12 + mDelegate.getMinYear();\n            int month = (position + mDelegate.getMinYearMonth() - 1) % 12 + 1;\n            BaseMonthView view;\n            try {\n                Constructor constructor = mDelegate.getMonthViewClass().getConstructor(Context.class);\n                view = (BaseMonthView) constructor.newInstance(getContext());\n            } catch (Exception e) {\n                e.printStackTrace();\n                return new DefaultMonthView(getContext());\n            }\n            view.mMonthViewPager = MonthViewPager.this;\n            view.mParentLayout = mParentLayout;\n            view.setup(mDelegate);\n            view.setTag(position);\n            view.initMonthWithDate(year, month);\n            view.setSelectedCalendar(mDelegate.mSelectedCalendar);\n            container.addView(view);\n            return view;\n        }\n\n        @Override\n        public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {\n            BaseView view = (BaseView) object;\n            view.onDestroy();\n            container.removeView(view);\n        }","sourceCodeStart":606,"sourceCodeEnd":642,"githubUrl":"https://github.com/huanghaibin-dev/CalendarView/blob/f5479ea3baefdbba2453cea19a208eca83baeb9e/calendarview/src/main/java/com/haibin/calendarview/MonthViewPager.java#L606-L642","documentation":"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.","triggerScenarios":"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.","commonSituations":"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.","solutions":["Give the class a public constructor taking Context and keep it lightweight (no casting to Activity).","Make the class top-level or static nested and public.","Check logcat for the printed exception (NoSuchMethodException, InvocationTargetException, etc.).","Add a keep rule for the class and its constructor.","If a constructor throws, wrap its body in try/catch or move fragile initialization to onMeasure/onDraw."],"exampleFix":"// before\npublic CustomMonthView(Context context) {\n    super(context);\n    ((MyActivity) context).getData(); // throws ClassCastException at instantiation\n}\n// after\npublic CustomMonthView(Context context) {\n    super(context);\n    // defer data access; obtain via listener/setup after construction\n}","handlingStrategy":"fallback","validationCode":"Class<?> cls = Class.forName(\"com.example.CustomMonthView\");\ncls.getConstructor(Context.class); // throws early if reflection will fail at bind time\n","typeGuard":"static boolean instantiableMonthView(Class<?> cls) {\n    try {\n        return BaseMonthView.class.isAssignableFrom(cls)\n            && cls.getConstructor(Context.class) != null;\n    } catch (NoSuchMethodException e) { return false; }\n}","tryCatchPattern":"// The library already falls back to DefaultMonthView; add your own guard:\ntry {\n    Constructor<?> ctor = CustomMonthView.class.getConstructor(Context.class);\n    ctor.newInstance(context);\n} catch (Throwable t) {\n    Log.w(\"Calendar\", \"CustomMonthView unavailable, default used\", t);\n}","preventionTips":["Avoid casting Context to Activity inside the view constructor.","Declare the class public and static; never anonymous or inner.","Do heavy work in setup()/onDraw, not the constructor.","Add a ProGuard keep rule for the constructor signature.","Visually verify the custom month view in a release build."],"tags":["android","reflection","fallback","month-view"],"backgroundTag":"class-not-found","analyzedSha":"f5479ea3baefdbba2453cea19a208eca83baeb9e","analyzedAt":"2026-09-11T10:11:54.823Z","contentChangedAt":"2026-09-11T10:11:54.823Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}