在 android studio 的 viewPager 中设置扩展 FragmentPagerAdapter 的 ViewPagerAdapter 时出现异常

Question

我在同一 activity 上有一个抽屉布局和选项卡布局。添加导航抽屉后，应用程序运行正常，但在向我的应用程序添加选项卡布局代码后，应用程序崩溃并抛出我无法理解的空指针异常。下面是我的代码：

MainActivity

package kbg.com.kbgpos;

import android.support.annotation.Nullable;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;


public class MainActivity extends AppCompatActivity {
Toolbar toolbar;
DrawerLayout drawerLayout;
ActionBarDrawerToggle actionBarDrawerToggle;
TabLayout tabLayout;
ViewPager viewPager;
ViewPagerAdapter viewPagerAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar=(Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        drawerLayout=(DrawerLayout) findViewById(R.id.drawer_layout);
        actionBarDrawerToggle=new ActionBarDrawerToggle(this,drawerLayout,toolbar,R.string.drawer_open,R.string.drawer_close);
        actionBarDrawerToggle.getDrawerArrowDrawable().setColor(getResources().getColor(R.color.hamburgerColor));
        drawerLayout.setDrawerListener(actionBarDrawerToggle);
        tabLayout=(TabLayout) findViewById(R.id.tabLayout);
        viewPager=(ViewPager) findViewById(R.id.view_pager);
        viewPagerAdapter=new ViewPagerAdapter(getSupportFragmentManager());
        viewPagerAdapter.addFragments(new Personal_Info_Fragment(),"Personal Info");
        viewPagerAdapter.addFragments(new EducationalExperience_Info_Fragment(),"Educational_Exp Info");
        viewPagerAdapter.addFragments(new OtherInfo_Fragment(),"Other Info");
        viewPager.setAdapter(viewPagerAdapter);
        tabLayout.setupWithViewPager(viewPager);
    }

    @Override
    protected void onPostCreate(@Nullable Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        actionBarDrawerToggle.syncState();
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:id="@+id/drawer_layout">

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <include
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        layout="@layout/toolbar_layout"
        android:id="@+id/toolbar"></include>

    <android.support.design.widget.TabLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/tabLayout"
        app:tabMode="fixed"
        app:tabGravity="fill">

    </android.support.design.widget.TabLayout>

</android.support.design.widget.AppBarLayout>

 <android.support.v4.view.ViewPager
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:id="@+id/viewPager">

 </android.support.v4.view.ViewPager>

    <android.support.design.widget.NavigationView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/navigation_view"
        android:layout_gravity="start"
        app:headerLayout="@layout/navigation_drawer_header"
        app:itemIconTint="#006699"
        app:menu="@menu/drawer_menu">

    </android.support.design.widget.NavigationView>

</android.support.v4.widget.DrawerLayout>

ViewPagerAdapter

package kbg.com.kbgpos;

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

import java.util.ArrayList;

public class ViewPagerAdapter extends FragmentPagerAdapter {
    ArrayList<Fragment> fragments=new ArrayList<>();
    ArrayList<String> tabTitles=new ArrayList<>();

    public void addFragments(Fragment fragments,String titles){
        this.fragments.add(fragments);
        this.tabTitles.add(titles);
    }

    public ViewPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return fragments.get(position);
    }

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

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles.get(position);
    }
}

异常

08-15 22:10:26.389 31693-31693/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: kbg.com.kbgpos, PID: 31693
    java.lang.RuntimeException: Unable to start activity ComponentInfo{kbg.com.kbgpos/kbg.com.kbgpos.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2747)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2808)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1541)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:165)
        at android.app.ActivityThread.main(ActivityThread.java:6365)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:883)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
        at kbg.com.kbgpos.MainActivity.onCreate(MainActivity.java:36)
        at android.app.Activity.performCreate(Activity.java:6852)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2700)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2808) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1541) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:165) 
        at android.app.ActivityThread.main(ActivityThread.java:6365) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:883) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)

请帮助我是这个领域的新手，已经检查了很多链接但找不到任何帮助。

Answer 1

在您的 xml 文件中修复此行：

viewPager=(ViewPager) findViewById(R.id.view_pager);

给这个id：

viewPager = (ViewPager) findViewById(R.id.viewPager);

在 android studio 的 viewPager 中设置扩展 FragmentPagerAdapter 的 ViewPagerAdapter 时出现异常

Exception on setting ViewPagerAdapter that extends FragmentPagerAdapter in viewPager in android studio

android

android-studio

android-viewpager

android-tablayout