Question

每当我试图调用viewpager.setAdapter时，我都会遇到问题，每当我运行我的应用程序时，它都会崩溃。MainActiviy.java:46，当我点击我的日志猫上的蓝色链接时，它需要我到我调用的viewpager.setAdapter方法。以下是我的代码。

MainActivity上课

public class MainActivity extends FragmentActivity implements View.OnClickListener {


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

setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

private static final String TAG_START_CAMERA = "Start Camera";
private static final String TAG_START_MUSIC = "Start Music";
private static final String TAG_START_USER_MENU = "Start User Menu";
private Toolbar toolbar;

    Toolbar toolbar = (Toolbar) findViewById(R.id.app_bar);

    ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
    viewPager.setAdapter(new MyFragmentPagerAdapter(getSupportFragmentManager()));***"This is the error line"***

  PagerSlidingTabStrip tabStrip = (PagerSlidingTabStrip)findViewById(R.id.tabs);
    tabStrip.setViewPager(viewPager); } }

activity_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto">

   <include 
    android:id="@+id/app_bar"
    layout="@layout/app_bar" />       

<com.astuetz.PagerSlidingTabStrip
    android:id="@+id/tabs"
    android:layout_width="wrap_content"
    android:layout_height="55dp"
    android:layout_alignParentEnd="true"
    android:background="@color/primaryColor"
    app:pstsDividerColor="@color/colorPrimarySecondary"
    app:pstsIndicatorColor="@color/colorPrimarySecondary"
    app:pstsDeactivateIconColor="#66323232"
    app:pstsActivateIconColor="@color/colorPrimarySecondary"
    app:pstsTabSwitch="true"
    app:pstsIndicatorHeight="2dp"
    app:pstsShouldExpand="true"
    app:pstsUnderlineHeight="2dp"/>

   <android.support.v4.view.ViewPager
       android:id="@+id/pager"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:layout_below="@+id/app_bar"
       android:layout_alignParentLeft="true"
       android:layout_alignParentStart="true"
       android:layout_marginTop="13dp" /> </RelativeLayout>

我的LogCat

06-29 08:33:11.034  24717-24717/? E/AndroidRuntime:FATAL EXCEPTION:main
java.lang.RuntimeException: Unable to start activity   ComponentInfo{com.example.lilstiikz.wehr/com.example.lilstiikz.wehr.MainActivity}: java.lang.NullPointerException  Caused by: java.lang.NullPointerException
            at com.example.lilstiikz.wehr.MainActivity.onCreate(MainActivity.java:46)
            at android.app.Activity.performCreate(Activity.java:5179)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access$700(ActivityThread.java:143)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4950)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

问题是viewPager为空，因为findViewById(R.id.pager)返回null。反过来的原因是，正如Harish上面所说，你用setContentView设置了错误的布局。

将来，您可以通过添加以下内容来自行调试NullPointerException

if(viewPager == null){ Log.e("MainActivity", "viewPager should not be null"); }

您怀疑可能导致异常的任何内容。

Answer 2

将setContentView(R.layout.activity_main_appbar);更改为setContentView(R.layout.activity_main);

更新：

对于多页滑块标签条。

com.astuetz.PagerSlidingTabStrip tabStrip = (com.astuetz.PagerSlidingTabStrip)findViewById(R.id.tabs);
    tabStrip.setViewPager(viewPager);

viewPager.setAdapter上的空指针执行（new MyFragmentPagerAdapter（getSupportFragmentManager（）））;

2 个答案: