TabsAdapter.java

package org.ohmage.ui;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabWidget;
import android.widget.TextView;

import org.ohmage.R;
import org.ohmage.logprobe.Analytics;

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.
 */
public class TabsAdapter extends FragmentPagerAdapter
implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
	private final Context mContext;
	private final TabHost mTabHost;
	private final ViewPager mViewPager;
	private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
	private final ArrayList<Fragment> mFragments = new ArrayList<Fragment>();

	static final class TabInfo {
		private final String tag;
		private final Class<?> clss;
		private final Bundle args;

		TabInfo(String _tag, Class<?> _class, Bundle _args) {
			tag = _tag;
			clss = _class;
			args = _args;
		}
	}

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

		public DummyTabFactory(Context context) {
			mContext = context;
		}

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

	public TabsAdapter(FragmentActivity activity, TabHost tabHost, ViewPager pager) {
		super(activity.getSupportFragmentManager());
		mContext = activity;
		mTabHost = tabHost;
		mViewPager = pager;
		mTabHost.setOnTabChangedListener(this);
		mViewPager.setAdapter(this);
		mViewPager.setOnPageChangeListener(this);
	}

	public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle args) {
		tabSpec.setContent(new DummyTabFactory(mContext));
		String tag = tabSpec.getTag();

		TabInfo info = new TabInfo(tag, clss, args);
		mTabs.add(info);
		mTabHost.addTab(tabSpec);
		notifyDataSetChanged();
	}

	/**
	 * Automatically adds a tab with the current text with the default button theme
	 */
	 public void addTab(String text, Class<?> clss, Bundle args) {
		LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
		TextView view = (TextView) inflater.inflate(R.layout.tab_indicator, mTabHost.getTabWidget(), false);
		view.setText(text.toUpperCase());
		addTab(mTabHost.newTabSpec(text.toLowerCase()).setIndicator(view), clss, args);
	 }

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

	 @Override
	 public Fragment getItem(int position) {
		 if(mFragments.size() <= position) {
			 TabInfo info = mTabs.get(position);
			 mFragments.add(position, Fragment.instantiate(mContext, info.clss.getName(), info.args));
		 }
		 return mFragments.get(position);
	 }

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

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

	 @Override
	 public void onPageSelected(int position) {
		 if(mPrevState == 0)
			 Analytics.widget(mViewPager.getContext(), "Filter Button To: " + position);
		 else
			 Analytics.widget(mViewPager.getContext(), "Swipe To: " + 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 = mTabHost.getTabWidget();
		 int oldFocusability = widget.getDescendantFocusability();
		 widget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
		 mTabHost.setCurrentTab(position);
		 widget.setDescendantFocusability(oldFocusability);
	 }

	 private int mState;
	 private int mPrevState;

	 @Override
	 public void onPageScrollStateChanged(int state) {
		 mPrevState = mState;
		 mState = state;
	 }
}