Modify the main activity, AndroidViewPagerActivity.java, to add a method switchFragment(int target) to call mViewPager.setCurrentItem(target) using Java code. Also we have to comment super.onSaveInstanceState(outState) in onSaveInstanceState(Bundle outState) method to prevent NullPointerException of ViewPager when change orientation.
package com.exercise.AndroidViewPager;
import java.util.ArrayList;
import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
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;
public class AndroidViewPagerActivity extends FragmentActivity {
ViewPager mViewPager;
TabsAdapter mTabsAdapter;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mViewPager = new ViewPager(this);
mViewPager.setId(R.id.pager);
setContentView(mViewPager);
final ActionBar bar = getActionBar();
bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
bar.setDisplayOptions(0, ActionBar.DISPLAY_SHOW_TITLE);
mTabsAdapter = new TabsAdapter(this, mViewPager);
mTabsAdapter.addTab(bar.newTab().setText("Fragment A"),
MyFragmentA.class, null);
mTabsAdapter.addTab(bar.newTab().setText("Fragment B"),
MyFragmentB.class, null);
mTabsAdapter.addTab(bar.newTab().setText("Fragment C"),
MyFragmentC.class, null);
if (savedInstanceState != null) {
bar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
//super.onSaveInstanceState(outState);
outState.putInt("tab", getActionBar().getSelectedNavigationIndex());
}
public static class TabsAdapter extends FragmentPagerAdapter
implements ActionBar.TabListener, ViewPager.OnPageChangeListener {
private final Context mContext;
private final ActionBar mActionBar;
private final ViewPager mViewPager;
private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
static final class TabInfo {
private final Class<?> clss;
private final Bundle args;
TabInfo(Class<?> _class, Bundle _args) {
clss = _class;
args = _args;
}
}
public TabsAdapter(FragmentActivity activity, ViewPager pager) {
super(activity.getSupportFragmentManager());
mContext = activity;
mActionBar = activity.getActionBar();
mViewPager = pager;
mViewPager.setAdapter(this);
mViewPager.setOnPageChangeListener(this);
}
public void addTab(ActionBar.Tab tab, Class<?> clss, Bundle args) {
TabInfo info = new TabInfo(clss, args);
tab.setTag(info);
tab.setTabListener(this);
mTabs.add(info);
mActionBar.addTab(tab);
notifyDataSetChanged();
}
@Override
public void onPageScrollStateChanged(int state) {
// TODO Auto-generated method stub
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int position) {
// TODO Auto-generated method stub
mActionBar.setSelectedNavigationItem(position);
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
Object tag = tab.getTag();
for (int i=0; i<mTabs.size(); i++) {
if (mTabs.get(i) == tag) {
mViewPager.setCurrentItem(i);
}
}
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
return Fragment.instantiate(mContext, info.clss.getName(), info.args);
}
@Override
public int getCount() {
return mTabs.size();
}
}
void switchFragment(int target){
mViewPager.setCurrentItem(target);
}
}
Modify layout of fragment_a.xml to add buttons to switch page.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="It's Fragment A" />
<Button
android:id="@+id/swb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Switch to Fragment B"/>
<Button
android:id="@+id/swc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Switch to Fragment C"/>
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="@drawable/ic_launcher"/>
</LinearLayout>
Modify MyFragmentA.java to call switchFragment() in main activity when buttons clicked. To access main activity from separate fragment java class, we can call getActivity() method.
package com.exercise.AndroidViewPager;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
public class MyFragmentA extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View myFragmentView = inflater.inflate(R.layout.fragment_a, container, false);
Button btnSwB = (Button)myFragmentView.findViewById(R.id.swb);
btnSwB.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
((AndroidViewPagerActivity)getActivity()).switchFragment(1);
}});
Button btnSwC = (Button)myFragmentView.findViewById(R.id.swc);
btnSwC.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
((AndroidViewPagerActivity)getActivity()).switchFragment(2);
}});
return myFragmentView;
}
}
For other files, include MyFragmentB.java, fragment_b.xml, MyFragmentC.java, and fragment_c.xml, refer to the post "ViewPager".
Download the files.Next:
- Display the title in ActionBar
