Question

我使用了android工作室提供的标签活动示例，并将其修改为片段。

由于某种原因，当我尝试从ID中检索时，ViewPager对象具有空引用。

以下是代码：

public class POI extends Fragment implements ActionBar.TabListener {

    SectionsPagerAdapter mSectionsPagerAdapter;
    ViewPager mViewPager;

    public static POI newInstance() {
       POI fragment = new POI();
       return fragment;
    }


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_poi, container, false);

    final ActionBar actionBar = ((AppCompatActivity) getActivity()).getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    mSectionsPagerAdapter = new SectionsPagerAdapter(getActivity().getSupportFragmentManager());

    mViewPager = (ViewPager) getView().findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            actionBar.setSelectedNavigationItem(position);
        }
    });

    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {

        int resourceName = getResources().getIdentifier("POI_Section" + i, "string", getActivity().getPackageName());
        actionBar.addTab(
                actionBar.newTab()
                        .setText(resourceName)
                        .setTabListener(this));
    }
    actionBar.setDisplayShowHomeEnabled(false);
    actionBar.setDisplayShowTitleEnabled(false);

    return rootView;
}

这是日志：

12-10 20:29:14.506    1297-1297/abff.googlemapsappteste E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: abff.googlemapsappteste, PID: 1297
java.lang.RuntimeException: Unable to start activity ComponentInfo{abff.googlemapsappteste/abff.googlemapsappteste.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.support.v4.view.ViewPager.toString()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442)
        at android.app.ActivityThread.access$800(ActivityThread.java:156)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:211)
        at android.app.ActivityThread.main(ActivityThread.java:5389)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.support.v4.view.ViewPager.toString()' on a null object reference
        at abff.googlemapsappteste.POI.onCreateView(POI.java:49)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1026)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1207)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1572)
        at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:511)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1236)
        at android.app.Activity.performStart(Activity.java:6006)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2342)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442)
        at android.app.ActivityThread.access$800(ActivityThread.java:156)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:211)
        at android.app.ActivityThread.main(ActivityThread.java:5389)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)

Answer 1

让您的xml有用，但禁止尝试更改

mViewPager = (ViewPager) getView().findViewById(R.id.pager);

到

mViewPager = (ViewPager) rootView.findViewById(R.id.pager);

在选项卡式片段上具有空引用的ViewPager对象

1 个答案: