[MaterialDatePicker] Fix for issue that causes the month view not to …

…expand to show all days in a month.

Resolves #1676

PiperOrigin-RevId: 436812359

lib/java/com/google/android/material/datepicker/MonthAdapter.java

@@ -42,6 +42,12 @@ class MonthAdapter extends BaseAdapter {
    */
   static final int MAXIMUM_WEEKS = UtcDates.getUtcCalendar().getMaximum(Calendar.WEEK_OF_MONTH);
 
+  /** The maximum number of cells needed in the month grid view. */
+  private static final int MAXIMUM_GRID_CELLS =
+      UtcDates.getUtcCalendar().getMaximum(Calendar.DAY_OF_MONTH)
+          + UtcDates.getUtcCalendar().getMaximum(Calendar.DAY_OF_WEEK)
+          - 1;
+
   final Month month;
   /**
    * The {@link DateSelector} dictating the draw behavior of {@link #getView(int, View, ViewGroup)}.
@@ -76,7 +82,7 @@ public boolean hasStableIds() {
   @Nullable
   @Override
   public Long getItem(int position) {
-    if (position < month.daysFromStartOfWeekToFirstOfMonth() || position > lastPositionInMonth()) {
+    if (position < firstPositionInMonth() || position > lastPositionInMonth()) {
       return null;
     }
     return month.getDay(positionToDay(position));
@@ -88,16 +94,15 @@ public long getItemId(int position) {
   }
 
   /**
-   * Returns the number of days in a month plus the amount required to off-set for the first day to
-   * the correct position within the week.
+   * Returns the maximum number of item views needed to display a calender month.
    *
-   * <p>{@see MonthAdapter#firstPositionInMonth}.
+   * <p>{@see MonthAdapter#MAXIMUM_GRID_CELLS}.
    *
    * @return The maximum valid position index
    */
   @Override
   public int getCount() {
-    return month.daysInMonth + firstPositionInMonth();
+    return MAXIMUM_GRID_CELLS;
   }
 
   @NonNull
@@ -220,7 +225,7 @@ int firstPositionInMonth() {
    * not match the number of days in the month.
    */
   int lastPositionInMonth() {
-    return month.daysFromStartOfWeekToFirstOfMonth() + month.daysInMonth - 1;
+    return firstPositionInMonth() + month.daysInMonth - 1;
   }
 
   /**
@@ -231,7 +236,7 @@ int lastPositionInMonth() {
    *     less than {@link MonthAdapter#firstPositionInMonth()}.
    */
   int positionToDay(int position) {
-    return position - month.daysFromStartOfWeekToFirstOfMonth() + 1;
+    return position - firstPositionInMonth() + 1;
   }
 
   /** Returns the adapter index representing the provided day. */

lib/javatests/com/google/android/material/datepicker/MonthAdapterTest.java

@@ -17,6 +17,7 @@
 
 import com.google.android.material.R;
 
+import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
@@ -166,25 +167,25 @@ private void assertPositionsForDays(Map<MonthAdapter, Integer> localizedPosition
   @Test
   public void usItemCount() {
     setupLocalizedCalendars(Locale.US);
-    assertEquals(30, monthFeb2016.getCount());
-    assertEquals(31, monthJuly2018.getCount());
-    assertEquals(33, monthFeb2019.getCount());
+    assertThat(monthFeb2016.getCount()).isAtLeast(30);
+    assertThat(monthJuly2018.getCount()).isAtLeast(31);
+    assertThat(monthFeb2019.getCount()).isAtLeast(33);
   }
 
   @Test
   public void frItemCount() {
     setupLocalizedCalendars(Locale.FRANCE);
-    assertEquals(29, monthFeb2016.getCount());
-    assertEquals(37, monthJuly2018.getCount());
-    assertEquals(32, monthFeb2019.getCount());
+    assertThat(monthFeb2016.getCount()).isAtLeast(29);
+    assertThat(monthJuly2018.getCount()).isAtLeast(37);
+    assertThat(monthFeb2019.getCount()).isAtLeast(32);
   }
 
   @Test
   public void ilItemCount() {
     setupLocalizedCalendars(ISRAEL);
-    assertEquals(30, monthFeb2016.getCount());
-    assertEquals(31, monthJuly2018.getCount());
-    assertEquals(33, monthFeb2019.getCount());
+    assertThat(monthFeb2016.getCount()).isAtLeast(30);
+    assertThat(monthJuly2018.getCount()).isAtLeast(31);
+    assertThat(monthFeb2019.getCount()).isAtLeast(33);
   }
 
   @Test