[DatePicker] Fix wrong month title with certain months

The issue is caused by failing to correctly take the daylight saving time into account - internally we use UTC time to represent dates, however when generating month titles we try to calculate the time difference of the UTC time and the local time, which can result in off-by-one errors when the first day of the month is also the first day of the daylight saving time, e.g., April 1, 1979 in Poland. Fixes this by always using UTC time to generate month titles. Also clears the relevant implementation for a little bit since context is actually not required when we only need to format years and months. Resolves #1935 PiperOrigin-RevId: 413505587
material-components · Dec 2, 2021 · 62e8993 · 62e8993
1 parent 2e73d1a
commit 62e8993
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Showing 5 changed files with 11 additions and 17 deletions.
diff --git a/lib/java/com/google/android/material/datepicker/DateStrings.java b/lib/java/com/google/android/material/datepicker/DateStrings.java
@@ -15,7 +15,6 @@
  */
 package com.google.android.material.datepicker;
 
-import android.content.Context;
 import android.icu.text.DateFormat;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
@@ -26,17 +25,15 @@
 import java.util.Calendar;
 import java.util.Date;
 import java.util.Locale;
-import java.util.TimeZone;
 
 /** Util methods for formatting date strings for use in {@link MaterialDatePicker}. */
 class DateStrings {
 
   private DateStrings() {}
 
-  static String getYearMonth(Context context, long timeInMillis) {
-    int flags = DateUtils.FORMAT_SHOW_YEAR | DateUtils.FORMAT_NO_MONTH_DAY;
-    long offsetMillis = TimeZone.getDefault().getOffset(timeInMillis);
-    return DateUtils.formatDateTime(context, timeInMillis - offsetMillis, flags);
+  static String getYearMonth(long timeInMillis) {
+    int flags = DateUtils.FORMAT_SHOW_YEAR | DateUtils.FORMAT_NO_MONTH_DAY | DateUtils.FORMAT_UTC;
+    return DateUtils.formatDateTime(null, timeInMillis, flags);
   }
 
   static String getYearMonthDay(long timeInMillis) {

diff --git a/lib/java/com/google/android/material/datepicker/MaterialCalendar.java b/lib/java/com/google/android/material/datepicker/MaterialCalendar.java
@@ -390,7 +390,7 @@ public void onInitializeAccessibilityNodeInfo(
     yearFrame = root.findViewById(R.id.mtrl_calendar_year_selector_frame);
     dayFrame = root.findViewById(R.id.mtrl_calendar_day_selector_frame);
     setSelector(CalendarSelector.DAY);
-    monthDropSelect.setText(current.getLongName(root.getContext()));
+    monthDropSelect.setText(current.getLongName());
     recyclerView.addOnScrollListener(
         new OnScrollListener() {
           @Override

diff --git a/lib/java/com/google/android/material/datepicker/Month.java b/lib/java/com/google/android/material/datepicker/Month.java
@@ -15,7 +15,6 @@
  */
 package com.google.android.material.datepicker;
 
-import android.content.Context;
 import android.os.Parcel;
 import android.os.Parcelable;
 import androidx.annotation.IntDef;
@@ -189,9 +188,9 @@ Month monthsLater(int months) {
 
   /** Returns a localized String representation of the month name and year. */
   @NonNull
-  String getLongName(Context context) {
+  String getLongName() {
     if (longName == null) {
-      longName = DateStrings.getYearMonth(context, firstOfMonth.getTimeInMillis());
+      longName = DateStrings.getYearMonth(firstOfMonth.getTimeInMillis());
     }
     return longName;
   }

diff --git a/lib/java/com/google/android/material/datepicker/MonthsPagerAdapter.java b/lib/java/com/google/android/material/datepicker/MonthsPagerAdapter.java
@@ -37,7 +37,6 @@
  */
 class MonthsPagerAdapter extends RecyclerView.Adapter<MonthsPagerAdapter.ViewHolder> {
 
-  private final Context context;
   @NonNull private final CalendarConstraints calendarConstraints;
   private final DateSelector<?> dateSelector;
   private final OnDayClickListener onDayClickListener;
@@ -63,7 +62,6 @@ class MonthsPagerAdapter extends RecyclerView.Adapter<MonthsPagerAdapter.ViewHol
     int labelHeight =
         MaterialDatePicker.isFullscreen(context) ? MaterialCalendar.getDayHeight(context) : 0;
 
-    this.context = context;
     this.itemHeight = daysHeight + labelHeight;
     this.calendarConstraints = calendarConstraints;
     this.dateSelector = dateSelector;
@@ -106,7 +104,7 @@ public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType)
   @Override
   public void onBindViewHolder(@NonNull MonthsPagerAdapter.ViewHolder viewHolder, int position) {
     Month month = calendarConstraints.getStart().monthsLater(position);
-    viewHolder.monthTitle.setText(month.getLongName(viewHolder.itemView.getContext()));
+    viewHolder.monthTitle.setText(month.getLongName());
     final MaterialCalendarGridView monthGrid = viewHolder.monthGrid.findViewById(R.id.month_grid);
 
     if (monthGrid.getAdapter() != null && month.equals(monthGrid.getAdapter().month)) {
@@ -141,7 +139,7 @@ public int getItemCount() {
 
   @NonNull
   CharSequence getPageTitle(int position) {
-    return getPageMonth(position).getLongName(context);
+    return getPageMonth(position).getLongName();
   }
 
   @NonNull

diff --git a/lib/javatests/com/google/android/material/datepicker/MonthsPagerAdapterTest.java b/lib/javatests/com/google/android/material/datepicker/MonthsPagerAdapterTest.java
@@ -126,10 +126,10 @@ public void pageTitles() {
                 .build(),
             /* onDayClickListener= */ null);
     assertEquals(
-        feb2016.getLongName(context), monthsAdapter.getPageTitle(/* position= */ 0).toString());
+        feb2016.getLongName(), monthsAdapter.getPageTitle(/* position= */ 0).toString());
     assertEquals(
-        march2016.getLongName(context), monthsAdapter.getPageTitle(/* position= */ 1).toString());
+        march2016.getLongName(), monthsAdapter.getPageTitle(/* position= */ 1).toString());
     assertEquals(
-        april2016.getLongName(context), monthsAdapter.getPageTitle(/* position= */ 2).toString());
+        april2016.getLongName(), monthsAdapter.getPageTitle(/* position= */ 2).toString());
   }
 }