ui/views/EffectiveNavigation/app/src/main/java/com/example/android/effectivenavigation/CollectionDemoActivity.java

/*
 * Copyright 2017 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.example.android.effectivenavigation;

import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.Locale;

public class CollectionDemoActivity extends AppCompatActivity {

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_collection_demo);

        // Set up the app bar
        final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null) {
            actionBar.setDisplayHomeAsUpEnabled(true);
        }

        // Create an adapter that when requested, will return a fragment representing an object in
        // the collection.
        //
        // ViewPager and its adapters use support library fragments, so we must use
        // getSupportFragmentManager.
        final DemoCollectionPagerAdapter adapter =
                new DemoCollectionPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager, attaching the adapter.
        final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
        viewPager.setAdapter(adapter);

        final TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
    }

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide fragments representing
     * each object in a collection. We use a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}
     * derivative, which will destroy and re-create fragments as needed, saving and restoring their
     * state in the process. This is important to conserve memory and is a best practice when
     * allowing navigation between objects in a potentially large collection.
     */
    private static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {

        DemoCollectionPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int i) {
            Fragment fragment = new DemoObjectFragment();
            Bundle args = new Bundle();
            args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public int getCount() {
            // For this contrived example, we have a 100-object collection.
            return 100;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "Page " + (position + 1);
        }
    }

    /**
     * A placeholder fragment representing a section of the app, but that simply displays placeholder text.
     */
    public static class DemoObjectFragment extends Fragment {

        public static final String ARG_OBJECT = "object";

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_collection_object, container, false);
            Bundle args = getArguments();
            ((TextView) rootView.findViewById(android.R.id.text1)).setText(
                    String.format(Locale.US, "%d", args.getInt(ARG_OBJECT)));
            return rootView;
        }
    }
}