TabsAdapter.java

/*
**
** Copyright 2013, 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 org.fdroid.fdroid.privileged.views;

import android.app.Activity;
import android.content.Context;
import android.graphics.Rect;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabWidget;

import java.util.ArrayList;
import java.util.List;

/**
 * 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.
 */
class TabsAdapter extends PagerAdapter
        implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
    private final Context context;
    private final TabHost tabHost;
    private final ViewPager viewPager;
    private final List<View> tabs = new ArrayList<>();
    private final Rect tempRect = new Rect();
    private TabHost.OnTabChangeListener onTabChangeListener;

    static class DummyTabFactory implements TabHost.TabContentFactory {
        private final Context context;

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

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

    TabsAdapter(Activity activity, TabHost tabHost, ViewPager pager) {
        context = activity;
        this.tabHost = tabHost;
        viewPager = pager;
        this.tabHost.setOnTabChangedListener(this);
        viewPager.setAdapter(this);
        viewPager.setOnPageChangeListener(this);
    }

    public void addTab(TabHost.TabSpec tabSpec, View view) {
        tabSpec.setContent(new DummyTabFactory(context));
        tabs.add(view);
        tabHost.addTab(tabSpec);
        notifyDataSetChanged();
    }

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

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        View view = tabs.get(position);
        container.addView(view);
        return view;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((View) object);
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    public void setOnTabChangedListener(TabHost.OnTabChangeListener listener) {
        onTabChangeListener = listener;
    }

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

    @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 widget = tabHost.getTabWidget();
        int oldFocusability = widget.getDescendantFocusability();
        widget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
        tabHost.setCurrentTab(position);
        widget.setDescendantFocusability(oldFocusability);

        // Scroll the current tab into visibility if needed.
        View tab = widget.getChildTabViewAt(position);
        tempRect.set(tab.getLeft(), tab.getTop(), tab.getRight(), tab.getBottom());
        widget.requestRectangleOnScreen(tempRect, false);

        // Make sure the scrollbars are visible for a moment after selection
        final View contentView = tabs.get(position);
        if (contentView instanceof CaffeinatedScrollView) {
            ((CaffeinatedScrollView) contentView).awakenScrollBars();
        }
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
}