动作条产生的NullPointerException

Question

我正在此错误显示java.lang.NullPointerException：尝试上的空对象引用

package com.surbhi.oopscourier.driver; 

import android.app.ActionBar; 
import android.app.FragmentTransaction; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.view.ViewPager; 

import com.surbhi.oopscourier.R; 

public class GeneralFiles extends FragmentActivity { 
    ViewPager Tab; 
    TabPagerAdapter TabAdapter; 
    ActionBar actionBar; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_general_files); 

     TabAdapter = new TabPagerAdapter(getSupportFragmentManager()); 

     Tab = (ViewPager)findViewById(R.id.pager); 
     Tab.setOnPageChangeListener(
       new ViewPager.SimpleOnPageChangeListener() { 
        @Override 
        public void onPageSelected(int position) { 

         actionBar = getActionBar(); 
         actionBar.setSelectedNavigationItem(position);     } 
       }); 
     Tab.setAdapter(TabAdapter); 

     actionBar = getActionBar(); 
     //Enable Tabs on Action Bar 
     actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 
     ActionBar.TabListener tabListener = new ActionBar.TabListener(){ 

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

      } 

      @Override 
      public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) { 

       Tab.setCurrentItem(tab.getPosition()); 
      } 

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

      }}; 
     //Add New Tab 
     actionBar.addTab(actionBar.newTab().setText("Android").setTabListener(tabListener)); 
     actionBar.addTab(actionBar.newTab().setText("iOS").setTabListener(tabListener)); 
     actionBar.addTab(actionBar.newTab().setText("Windows").setTabListener(tabListener)); 

    } 




} 

调用虚拟方法 '无效android.app.ActionBar.setNavigationMode（INT）'

操作栏的问题和选项卡不显示

com.sourcey.materialloginexample E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.sourcey.materialloginexample, PID: 1189 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sourcey.materialloginexample/com.surbhi.oopscourier.driver.GeneralFiles}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5443) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference 
at com.surbhi.oopscourier.driver.GeneralFiles.onCreate(GeneralFiles.java:36) 
at android.app.Activity.performCreate(Activity.java:6259) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)  
at android.app.ActivityThread.-wrap11(ActivityThread.java)  
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)  
at android.os.Handler.dispatchMessage(Handler.java:102)  
at android.os.Looper.loop(Looper.java:148)  
at android.app.ActivityThread.main(ActivityThread.java:5443)  
at java.lang.reflect.Method.invoke(Native Method)  
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)  
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)  

操作栏异常，也请告诉我的清单中的代码显示操作栏和主题也。标签不显示，这些都是错误。

Answer 1

尝试使用getSupportActionBar()而不是getActionBar()。

Answer 2

使用getSupportActionBar()而不是getActionBar()。