Question

在发帖之前，我检查了很多问题，但他们没有帮助我。大多数答案都说ViewPager的布局不同，所以这就是它生成空指针异常的原因。

下面是我的stacktrace

E/AndroidRuntime: FATAL EXCEPTION: main Process: pdfshare.hemanthreddy.com.pdfshare, PID: 29092
java.lang.RuntimeException: Unable to start activity ComponentInfo{pdfshare.hemanthreddy.com.pdfshare/pdfshare.hemanthreddy.com.pdfshare.activities.HomeScreen}: 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:2426)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$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.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
at pdfshare.hemanthreddy.com.pdfshare.activities.HomeScreen.onCreate(HomeScreen.java:39)
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.access$900(ActivityThread.java:154) 
at android.app.ActivityThread$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)

这是我已声明xml的{{1}}文件的 activity_home_screen.xml

Viewpager

活动类 HomeScreen.java

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="pdfshare.hemanthreddy.com.pdfshare.activities.HomeScreen">
<android.support.v4.view.ViewPager
    android:id="@+id/viewpagerhome"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"  />
 </RelativeLayout>

E / obj：不为空 E / pager：null 不知道为什么寻呼机对象为空。请帮帮我，我试图在viewPager中加载4个片段，谢谢。

Answer 1

这意味着MyPagerAdapter类型的变量obj为null，返回值有错误。

MyPagerAdapter obj = new MyPagerAdapter(getSupportFragmentManager());

该行是问题，问题可能在您的自定义适配器或您的获取支持片段管理器中。如果他们正在工作，obj将不会为空。

我打赌如果你注释掉那条线和setadapter线它不会再崩溃，除非你有更大的问题

ViewPager obj为null，即使它正确启动并且也存在于定义的布局xml中

1 个答案: