material-components_material-components-android/lib/java/com/google/android/material/picker/MonthsPagerAdapter.java

/*
 * 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.picker;

import android.database.DataSetObserver;
import androidx.annotation.NonNull;
import com.google.android.material.picker.MaterialCalendar.OnDayClickListener;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;
import android.util.SparseArray;
import android.view.ViewGroup;

/**
 * Manages the instances of {@link MonthFragment}, capping memory usage.
 *
 * @hide
 */
class MonthsPagerAdapter extends FragmentStatePagerAdapter {

  private final Month firstPage;
  private final Month lastPage;
  private final int startIndex;
  private final GridSelector<?> gridSelector;
  private final SparseArray<DataSetObserver> observingFragments = new SparseArray<>();
  private final OnDayClickListener onDayClickListener;

  /**
   * Creates a new {@link FragmentStatePagerAdapter} that manages the instances of {@link
   * MonthFragment}.
   *
   * @param fragmentManager A {@link FragmentManager} for the {@link MonthFragment} objects. {@see
   *     Fragment#getChildFragmentManager()}
   * @param gridSelector The {@link GridSelector} that controls selection and highlights for all
   *     {@link MonthFragment} objects.
   * @param firstPage The earliest accessible {@link Month}. This {@link Month} will be at position
   *     0. {@link MonthsPagerAdapter#getItem}.
   * @param lastPage The latest accessible {@link Month}. Must be chronologically after or the same
   *     as {@code firstPage}.
   * @param startPage The starting {@link Month} displayed. Must be chronologically between {@code
   *     firstPage} and {@code lastPage} inclusive.
   */
  MonthsPagerAdapter(
      FragmentManager fragmentManager,
      GridSelector<?> gridSelector,
      Month firstPage,
      Month lastPage,
      Month startPage,
      OnDayClickListener onDayClickListener) {
    super(fragmentManager);
    if (firstPage.compareTo(startPage) > 0) {
      throw new IllegalArgumentException("firstPage cannot be after startPage");
    }
    if (startPage.compareTo(lastPage) > 0) {
      throw new IllegalArgumentException("startPage cannot be after lastPage");
    }
    this.firstPage = firstPage;
    this.lastPage = lastPage;
    startIndex = firstPage.monthsUntil(startPage);
    this.gridSelector = gridSelector;
    this.onDayClickListener = onDayClickListener;
  }

  @Override
  public int getCount() {
    return firstPage.monthsUntil(lastPage) + 1;
  }

  @NonNull
  @Override
  public Fragment instantiateItem(@NonNull ViewGroup viewGroup, int position) {
    final MonthFragment monthFragment = (MonthFragment) super.instantiateItem(viewGroup, position);
    monthFragment.setOnDayClickListener(onDayClickListener);
    return monthFragment;
  }

  @Override
  public MonthFragment getItem(int position) {
    final MonthFragment monthFragment =
        MonthFragment.newInstance(firstPage.monthsLater(position), gridSelector);

    DataSetObserver dataSetObserver =
        new DataSetObserver() {
          @Override
          public void onChanged() {
            monthFragment.notifyDataSetChanged();
          }
        };
    registerDataSetObserver(dataSetObserver);
    observingFragments.put(position, dataSetObserver);
    return monthFragment;
  }

  @Override
  public void destroyItem(@NonNull ViewGroup viewGroup, int position, @NonNull Object o) {
    DataSetObserver dataSetObserver = observingFragments.get(position);
    if (dataSetObserver != null) {
      observingFragments.remove(position);
      unregisterDataSetObserver(dataSetObserver);
    }
    super.destroyItem(viewGroup, position, o);
  }

  /** Returns the position index of the {@link Month} startPage provided on construction. */
  int getStartPosition() {
    return startIndex;
  }

  @Override
  @NonNull
  public CharSequence getPageTitle(int position) {
    return getPageMonth(position).getLongName();
  }

  Month getPageMonth(int position) {
    return firstPage.monthsLater(position);
  }
}