选择android中的选项卡

Question

当我写这段代码时

viewPager.setCurrentItem(tab.getPosition());

在ontabselected方法中，我的应用程序崩溃了。总的来说，我的申请工作正常。这是我的完整代码

package com.hamza.aurasalon;

import android.annotation.TargetApi;
import android.app.ActionBar;
import android.app.ActionBar.TabListener;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBar.Tab;
import android.support.v4.app.FragmentTransaction;

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class AboutUs extends FragmentActivity implements TabListener {

private ActionBar actionBar;
private ViewPager viewPager;

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.aboutus);
    intialization();

}

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void intialization() {
    // TODO Auto-generated method stub

    actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    ActionBar.Tab tab1 = actionBar.newTab();
    tab1.setText("MUMTAZ ANWAR");
    tab1.setTabListener(this);

    ActionBar.Tab tab2 = actionBar.newTab();
    tab2.setText("CREDIENTIALS");
    tab2.setTabListener(this);

    actionBar.addTab(tab1);
    actionBar.addTab(tab2);

    viewPager = (ViewPager) findViewById(R.id.pagger);
    viewPager.setAdapter(new MyAdapter(getSupportFragmentManager()));
    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int arg0) {
            // TODO Auto-generated method stub
            actionBar.setSelectedNavigationItem(arg0);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
            // TODO Auto-generated method stub
        }
    });

}

@Override
public void onTabReselected(android.app.ActionBar.Tab tab,
        android.app.FragmentTransaction ft) {
    // TODO Auto-generated method stub

}

@Override
public void onTabSelected(android.app.ActionBar.Tab tab,
        android.app.FragmentTransaction ft) {
    // TODO Auto-generated method stub
    // viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(android.app.ActionBar.Tab tab,
        android.app.FragmentTransaction ft) {
    // TODO Auto-generated method stub

}

}

类MyAdapter扩展了FragmentPagerAdapter {

public MyAdapter(FragmentManager fm) {
    super(fm);
    // TODO Auto-generated constructor stub
}

@Override
public Fragment getItem(int arg0) {
    // TODO Auto-generated method stub

    Fragment fragment = null;
    if (arg0 == 0) {

        fragment = new BlankFragment();
    }

    if (arg0 == 1) {

        fragment = new BlankFragmenta();
    }

    return fragment;
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return 2;
}

}

logcat错误

   07-09 15:52:09.837: W/dalvikvm(13392): threadid=1: thread exiting with uncaught exception (group=0x415ba9a8)
   07-09 15:52:09.850: E/AndroidRuntime(13392): FATAL EXCEPTION: main
07-09 15:52:09.850: E/AndroidRuntime(13392): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.hamza.aurasalon/com.hamza.aurasalon.AboutUs}: java.lang.NullPointerException
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2343)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2395)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread.access$600(ActivityThread.java:162)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1364)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.os.Handler.dispatchMessage(Handler.java:107)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.os.Looper.loop(Looper.java:194)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread.main(ActivityThread.java:5371)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at java.lang.reflect.Method.invokeNative(Native Method)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at java.lang.reflect.Method.invoke(Method.java:525)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at dalvik.system.NativeStart.main(Native Method)
07-09 15:52:09.850: E/AndroidRuntime(13392): Caused by: java.lang.NullPointerException
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.hamza.aurasalon.AboutUs.onTabSelected(AboutUs.java:85)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.android.internal.app.ActionBarImpl.selectTab(ActionBarImpl.java:570)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.android.internal.app.ActionBarImpl.addTab(ActionBarImpl.java:499)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.android.internal.app.ActionBarImpl.addTab(ActionBarImpl.java:485)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.hamza.aurasalon.AboutUs.intialization(AboutUs.java:47)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at com.hamza.aurasalon.AboutUs.onCreate(AboutUs.java:28)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.Activity.performCreate(Activity.java:5122)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
07-09 15:52:09.850: E/AndroidRuntime(13392):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
07-09 15:52:09.850: E/AndroidRuntime(13392):    ... 11 more