huanghaibin-dev/CalendarView · error

e.printStackTrace()

Error message

e.printStackTrace()

What it means

CalendarView.init() reflectively instantiates the custom WeekBar class configured via app:calendar_week_bar_view. The constructor lookup (Context argument) or newInstance fails, and the library swallows the exception with printStackTrace, leaving mWeekBar null, which then crashes on frameContent.addView(mWeekBar, 2) with a NullPointerException.

Solutions

1. Ensure the custom WeekBar class is public, top-level or static, and has an explicit public constructor taking Context: public MyWeekBar(Context context).
2. Check logcat for the swallowed stack trace (ClassNotFoundException / NoSuchMethodException) to identify the exact failure.
3. Add a ProGuard keep rule: -keep class com.example.MyWeekBar { public <init>(android.content.Context); }.
4. Verify app:calendar_week_bar_view in XML matches the fully-qualified class name exactly.
5. As a last resort, temporarily fall back to the default WeekBar (remove the XML attribute) to confirm the custom class is the problem.

Example fix

// before
public class CalendarActivity extends AppCompatActivity {
    class MyWeekBar extends WeekBar { public MyWeekBar(Context c){super(c);} }
}
// after
public class MyWeekBar extends WeekBar {
    public MyWeekBar(Context context) { super(context); }
}

// Before setting XML attribute, verify at startup:
Class<?> c = Class.forName("com.example.MyWeekBar");
if (!WeekBar.class.isAssignableFrom(c)) throw new IllegalStateException("Must extend WeekBar");
c.getConstructor(Context.class); // throws if constructor missing

static boolean isValidWeekBar(Class<?> cls) {
    return WeekBar.class.isAssignableFrom(cls)
        && java.lang.reflect.Modifier.isPublic(cls.getModifiers())
        && !cls.isMemberClass();
}

try {
    calendarView.setWeekBar(MyWeekBar.class);
} catch (Throwable t) {
    Log.e("Calendar", "Custom WeekBar failed, using default", t);
    // continue with library default
}

When it happens

Trigger: A custom WeekBar subclass is declared in XML (app:calendar_week_bar_view="com.example.MyWeekBar") but the class is not public, lacks a public MyWeekBar(Context) constructor, is an inner (non-static) class, or was ProGuard/R8-obfuscated or removed at build time.

Common situations: Developers subclass WeekBar inside an Activity as a non-static inner class; enabling minifyEnabled true without a keep rule for the custom view; typo in the fully-qualified class name; the custom class lives in a module not included as a dependency.

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/dd59d4c4464fafc3. Report an issue: GitHub.

Appendix: source

Thrown at calendarview/src/main/java/com/haibin/calendarview/CalendarView.java:108

        init(context);
    }

    /**
     * 初始化
     *
     * @param context context
     */
    private void init(Context context) {
        LayoutInflater.from(context).inflate(R.layout.cv_layout_calendar_view, this, true);
        FrameLayout frameContent = findViewById(R.id.frameContent);
        this.mWeekPager = findViewById(R.id.vp_week);
        this.mWeekPager.setup(mDelegate);

        try {
            Constructor constructor = mDelegate.getWeekBarClass().getConstructor(Context.class);
            mWeekBar = (WeekBar) constructor.newInstance(getContext());
        } catch (Exception e) {
            e.printStackTrace();
        }

        frameContent.addView(mWeekBar, 2);
        mWeekBar.setup(mDelegate);
        mWeekBar.onWeekStartChange(mDelegate.getWeekStart());

        this.mWeekLine = findViewById(R.id.line);
        this.mWeekLine.setBackgroundColor(mDelegate.getWeekLineBackground());
        LayoutParams lineParams = (LayoutParams) this.mWeekLine.getLayoutParams();
        lineParams.setMargins(mDelegate.getWeekLineMargin(),
                mDelegate.getWeekBarHeight(),
                mDelegate.getWeekLineMargin(),
                0);
        this.mWeekLine.setLayoutParams(lineParams);

        this.mMonthPager = findViewById(R.id.vp_month);
        this.mMonthPager.mWeekPager = mWeekPager;
        this.mMonthPager.mWeekBar = mWeekBar;

View on GitHub (pinned to f5479ea3ba)