Fixed MaterialDatePicker todayInUtcMilliseconds method.

- Used UtcDates to return the UTC milliseconds of today in local timezone.
- Previous method is replaced with thisMonthInUtcMilliseconds, which fits its function better.
Resolves #778

PiperOrigin-RevId: 283981946
(cherry picked from commit 77ce281)

Author: pekingme

catalog/java/io/material/catalog/datepicker/DatePickerMainDemoFragment.java

@@ -56,7 +56,7 @@ private static Calendar getClearedUtc() {
   }
 
   private void initSettings() {
-    today = MaterialDatePicker.todayInUtcMilliseconds();
+    today = MaterialDatePicker.thisMonthInUtcMilliseconds();
     Calendar calendar = getClearedUtc();
     calendar.setTimeInMillis(today);
     calendar.roll(Calendar.MONTH, 1);

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

@@ -294,7 +294,7 @@ public Builder setValidator(DateValidator validator) {
     @NonNull
     public CalendarConstraints build() {
       if (openAt == null) {
-        long today = MaterialDatePicker.todayInUtcMilliseconds();
+        long today = MaterialDatePicker.thisMonthInUtcMilliseconds();
         openAt = start <= today && today <= end ? today : start;
       }
       Bundle deepCopyBundle = new Bundle();

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

@@ -65,8 +65,15 @@ public final class MaterialDatePicker<S> extends DialogFragment {
   static final Object CANCEL_BUTTON_TAG = "CANCEL_BUTTON_TAG";
   static final Object TOGGLE_BUTTON_TAG = "TOGGLE_BUTTON_TAG";
 
-  /** Returns a value of UTC milliseconds representing today for the device's current timezone. */
+  /** Returns the UTC milliseconds representing the first moment of today in local timezone. */
   public static long todayInUtcMilliseconds() {
+    return UtcDates.getTodayCalendar().getTimeInMillis();
+  }
+
+  /**
+   * Returns the UTC milliseconds representing the first moment in current month in local timezone.
+   */
+  public static long thisMonthInUtcMilliseconds() {
     return Month.today().timeInMillis;
   }
 

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

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.material.datepicker;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.time.Duration;
+import java.util.Calendar;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+/** Test for {@link com.google.android.material.datepicker.MaterialDatePicker}. */
+@RunWith(RobolectricTestRunner.class)
+public class MaterialDatePickerTest {
+
+  private static final long ONE_DAY_MILLIS = Duration.ofDays(1).toMillis();
+
+  @Test
+  public void testTodayInUtcMilliseconds() {
+    long todayUtcMS = MaterialDatePicker.todayInUtcMilliseconds();
+    Calendar outputUtcTodayInCalendar = Calendar.getInstance(UtcDates.getTimeZone());
+    outputUtcTodayInCalendar.setTimeInMillis(todayUtcMS);
+    Calendar expectedUtcTodayInCalendar = Calendar.getInstance(UtcDates.getTimeZone());
+
+    // Assert fields finer than a day are stripped.
+    assertThat(todayUtcMS % ONE_DAY_MILLIS).isEqualTo(0);
+    // Assert this is the same date as today in UTC.
+    assertThat(outputUtcTodayInCalendar.get(Calendar.YEAR))
+        .isEqualTo(expectedUtcTodayInCalendar.get(Calendar.YEAR));
+    assertThat(outputUtcTodayInCalendar.get(Calendar.MONTH))
+        .isEqualTo(expectedUtcTodayInCalendar.get(Calendar.MONTH));
+    assertThat(outputUtcTodayInCalendar.get(Calendar.DATE))
+        .isEqualTo(expectedUtcTodayInCalendar.get(Calendar.DATE));
+  }
+
+  @Test
+  public void testThisMonthInUtcMilliseconds() {
+    long thisMonthUtcMS = MaterialDatePicker.thisMonthInUtcMilliseconds();
+    Calendar outputUtcThisMonthInCalendar = Calendar.getInstance(UtcDates.getTimeZone());
+    outputUtcThisMonthInCalendar.setTimeInMillis(thisMonthUtcMS);
+    Calendar expectedUtcThisMonthInCalendar = Calendar.getInstance(UtcDates.getTimeZone());
+
+    // Assert fields finer than a day are stripped.
+    assertThat(thisMonthUtcMS % ONE_DAY_MILLIS).isEqualTo(0);
+    // Assert this is the first day of this month in UTC.
+    assertThat(outputUtcThisMonthInCalendar.get(Calendar.YEAR))
+        .isEqualTo(expectedUtcThisMonthInCalendar.get(Calendar.YEAR));
+    assertThat(outputUtcThisMonthInCalendar.get(Calendar.MONTH))
+        .isEqualTo(expectedUtcThisMonthInCalendar.get(Calendar.MONTH));
+    assertThat(outputUtcThisMonthInCalendar.get(Calendar.DATE)).isEqualTo(1);
+  }
+}