[MaterialDatePicker][A11y] Disable next/prev button when the selected month is at the boundary

When user clicks on previous/next month button, the button will be disabled if the clicked month is at the boundary.

PiperOrigin-RevId: 738309727

Author: Material Design Team

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

@@ -347,6 +347,7 @@ void setCurrentMonth(Month moveTo) {
     } else {
       postSmoothRecyclerViewScroll(moveToPosition);
     }
+    updateNavigationButtonsEnabled(moveToPosition);
   }
 
   @Nullable
@@ -442,8 +443,12 @@ public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
             } else {
               currentItem = getLayoutManager().findLastVisibleItemPosition();
             }
-            current = monthsPagerAdapter.getPageMonth(currentItem);
+            Month moveToMonth = monthsPagerAdapter.getPageMonth(currentItem);
+            current = moveToMonth;
             monthDropSelect.setText(monthsPagerAdapter.getPageTitle(currentItem));
+
+            int currentMonthPosition = monthsPagerAdapter.getPosition(moveToMonth);
+            updateNavigationButtonsEnabled(currentMonthPosition);
           }
 
           @Override
@@ -468,21 +473,25 @@ public void onClick(View view) {
           @Override
           public void onClick(View view) {
             int currentItem = getLayoutManager().findFirstVisibleItemPosition();
-            if (currentItem + 1 < recyclerView.getAdapter().getItemCount()) {
-              setCurrentMonth(monthsPagerAdapter.getPageMonth(currentItem + 1));
-            }
+            setCurrentMonth(monthsPagerAdapter.getPageMonth(currentItem + 1));
           }
         });
     monthPrev.setOnClickListener(
         new OnClickListener() {
           @Override
           public void onClick(View view) {
             int currentItem = getLayoutManager().findLastVisibleItemPosition();
-            if (currentItem - 1 >= 0) {
-              setCurrentMonth(monthsPagerAdapter.getPageMonth(currentItem - 1));
-            }
+            setCurrentMonth(monthsPagerAdapter.getPageMonth(currentItem - 1));
           }
         });
+
+    int currentMonthPosition = monthsPagerAdapter.getPosition(current);
+    updateNavigationButtonsEnabled(currentMonthPosition);
+  }
+
+  private void updateNavigationButtonsEnabled(int currentMonthPosition) {
+    monthNext.setEnabled(currentMonthPosition + 1 < recyclerView.getAdapter().getItemCount());
+    monthPrev.setEnabled(currentMonthPosition - 1 >= 0);
   }
 
   private void postSmoothRecyclerViewScroll(final int position) {

tests/javatests/com/google/android/material/datepicker/MaterialDatePickerPagesTest.java

@@ -15,8 +15,14 @@
  */
 package com.google.android.material.datepicker;
 
+import static androidx.test.espresso.Espresso.onView;
+import static androidx.test.espresso.assertion.ViewAssertions.matches;
+import static androidx.test.espresso.matcher.ViewMatchers.isEnabled;
+import static androidx.test.espresso.matcher.ViewMatchers.withTagValue;
 import static com.google.android.material.datepicker.MaterialDatePickerTestUtils.findFirstVisibleItem;
 import static org.hamcrest.Matchers.lessThan;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.core.IsEqual.equalTo;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
@@ -141,4 +147,44 @@ public void accessibility_daySelection_notScrollable() {
 
     assertFalse(nodeInfo.isScrollable());
   }
+
+  @Test
+  public void previousButtonDisabledAtStartBoundary() {
+    MaterialDatePickerTestUtils.clickPrev();
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_PREV_TAG)))
+        .check(matches(not(isEnabled())));
+  }
+
+  @Test
+  public void nextButtonDisabledAtEndBoundary() {
+    MaterialDatePickerTestUtils.clickNext();
+    MaterialDatePickerTestUtils.clickNext();
+    MaterialDatePickerTestUtils.clickNext();
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_NEXT_TAG)))
+        .check(matches(not(isEnabled())));
+  }
+
+  @Test
+  public void nextButtonEnabledAtStartBoundary() {
+    MaterialDatePickerTestUtils.clickPrev();
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_NEXT_TAG)))
+        .check(matches(isEnabled()));
+  }
+
+  @Test
+  public void previousButtonEnabledAtEndBoundary() {
+    MaterialDatePickerTestUtils.clickNext();
+    MaterialDatePickerTestUtils.clickNext();
+    MaterialDatePickerTestUtils.clickNext();
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_PREV_TAG)))
+        .check(matches(isEnabled()));
+  }
+
+  @Test
+  public void navigationButtonsEnabledInMiddleOfBoundary() {
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_NEXT_TAG)))
+        .check(matches(isEnabled()));
+    onView(withTagValue(equalTo(MaterialCalendar.NAVIGATION_NEXT_TAG)))
+        .check(matches(isEnabled()));
+  }
 }