OpenTracks/src/main/java/de/dennisguse/opentracks/TabsAdapter.java

/*
 * Copyright 2013q Google Inc.
 *
 * 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 de.dennisguse.opentracks;

import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabHost.TabContentFactory;
import android.widget.TabWidget;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentActivity;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.viewpager.widget.ViewPager;

import java.util.ArrayList;

/**
 * This is a helper class that implements the management of tabs and all details
 * of connecting a ViewPager with associated TabHost. It relies on a trick.
 * Normally a tab host has a simple API for supplying a View or Intent that each
 * tab will show. This is not sufficient for switching between pages. So instead
 * we make the content part of the tab host 0dp high (it is not shown) and the
 * TabsAdapter supplies its own dummy view to show as the tab content. It
 * listens to changes in tabs, and takes care of switch to the correct paged in
 * the ViewPager whenever the selected tab changes.
 * <p>
 * Copied from the FragmentTabsPager sample in the support library.
 *
 * @author Jimmy Shih
 */
//TODO Rework or better remove.
public class TabsAdapter extends FragmentPagerAdapter implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {

    private final Context context;
    private final TabHost tabHost;
    private final ViewPager viewPager;
    private final ArrayList<TabInfo> tabInfos = new ArrayList<>();

    public TabsAdapter(FragmentActivity activity, TabHost tabHost, ViewPager viewPager) {
        super(activity.getSupportFragmentManager());
        this.context = activity;
        this.tabHost = tabHost;
        this.viewPager = viewPager;
        this.tabHost.setOnTabChangedListener(this);
        this.viewPager.setAdapter(this);
        this.viewPager.setOnPageChangeListener(this);
    }

    public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle bundle) {
        tabSpec.setContent(new DummyTabFactory(context));

        TabInfo info = new TabInfo(clss, bundle);

        tabInfos.add(info);
        tabHost.addTab(tabSpec);
        notifyDataSetChanged();
    }

    @Override
    public int getCount() {
        return tabInfos.size();
    }

    @Override
    @NonNull
    public Fragment getItem(int position) {
        TabInfo info = tabInfos.get(position);
        return Fragment.instantiate(context, info.clss.getName(), info.bundle);
    }

    @Override
    public void onTabChanged(String tabId) {
        int position = tabHost.getCurrentTab();
        viewPager.setCurrentItem(position);
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        /*
         * Unfortunately when TabHost changes the current tab, it kindly also takes care of putting focus on it when not in touch mode.
         * The jerk. This hack  tries to prevent this from pulling focus out of our ViewPager.
         */
        TabWidget tabWidget = tabHost.getTabWidget();
        int oldFocusability = tabWidget.getDescendantFocusability();
        tabWidget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
        tabHost.setCurrentTab(position);
        tabWidget.setDescendantFocusability(oldFocusability);
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }

    /**
     * An object to hold a tab's info.
     *
     * @author Jimmy Shih
     */
    private static final class TabInfo {

        private final Class<?> clss;
        private final Bundle bundle;

        TabInfo(Class<?> clss, Bundle bundle) {
            this.clss = clss;
            this.bundle = bundle;
        }
    }

    /**
     * A dummy {@link TabContentFactory} that creates an empty view to satisfy the {@link TabHost} API.
     *
     * @author Jimmy Shih
     */
    private static class DummyTabFactory implements TabHost.TabContentFactory {

        private final Context context;

        DummyTabFactory(Context context) {
            this.context = context;
        }

        @Override
        public View createTabContent(String tag) {
            View view = new View(context);
            view.setMinimumWidth(0);
            view.setMinimumHeight(0);
            return view;
        }
    }
}