Android – 尝试在空对象引用上调用虚方法’void android.support.v4.app.Fragment.setMenuVisibility(boolean)’

概述以下是错误的完整堆栈跟踪： http://pastebin.com/5dQHkUw3 只有在我开始在项目中使用片段后才会出现错误,因为我想提供JSON提要.在我创建Tabs,NavigationDrawer等之前没事. MainActivity.java 公共类MainActivity扩展ActionBarActivity实现MaterialTabListener { private Toolba 以下是错误的完整堆栈跟踪： http://pastebin.com/5dQHkUw3

只有在我开始在项目中使用片段后才会出现错误,因为我想提供JsON提要.在我创建Tabs,NavigationDrawer等之前没事.

MainActivity.java

公共类MainActivity扩展ActionBaractivity实现MaterialTabListener {

private Toolbar mToolbar;private NavigationDrawerFragment mDrawerFragment;private DrawerLayout mDrawerLayout;private MaterialTabHost mTabHost;private VIEwPager mVIEwPager;public static final int SERVICES_ALL = 1;public static final int SERVICES_FEATURED = 2;public static final int SERVICES_NEW = 3;@OverrIDeprotected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentVIEw(R.layout.activity_main_appbar);    mToolbar = (Toolbar) findVIEwByID(R.ID.app_bar);    setSupportActionbar(mToolbar);    getSupportActionbar().setdisplayShowHomeEnabled(true);    mDrawerLayout = (DrawerLayout) findVIEwByID(R.ID.drawer_layout);    mDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager().findFragmentByID(R.ID.fragment_navigation_drawer);    mDrawerFragment.setUp(R.ID.fragment_navigation_drawer,mDrawerLayout,mToolbar);    mTabHost = (MaterialTabHost) findVIEwByID(R.ID.materialTabHost);    mVIEwPager = (VIEwPager) findVIEwByID(R.ID.vIEwPager);    MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());    mVIEwPager.setAdapter(adapter);    mVIEwPager.setonPagechangelistener(new VIEwPager.SimpleOnPagechangelistener(){        @OverrIDe        public voID onPageSelected(int position) {            mTabHost.setSelectednavigationItem(position);        }    });    for(int i=0; i<adapter.getCount(); i++ ){        mTabHost.addTab(                mTabHost.newTab().                        setText(adapter.getPageTitle(i)).                        setTabListener(this)        );    }}@OverrIDepublic voID onTabSelected(MaterialTab materialTab) {    mVIEwPager.setCurrentItem(materialTab.getposition());}@OverrIDepublic voID onTabReselected(MaterialTab materialTab) {}@OverrIDepublic voID onTabUnselected(MaterialTab materialTab) {}private class MyPagerAdapter extends FragmentStatePagerAdapter{    FragmentManager fragmentManager;    public MyPagerAdapter(FragmentManager fm) {        super(fm);        fragmentManager = fm;    }    @OverrIDe    public Fragment getItem(int num) {        Fragment fragment = null;        switch (num){            case SERVICES_ALL:                fragment = FragmentAll.newInstance("","");                break;            case SERVICES_FEATURED:                fragment = FragmentFeatured.newInstance("","");                break;            case SERVICES_NEW:                fragment = FragmentNew.newInstance("","");                break;        }        return fragment;    }    @OverrIDe    public int getCount() {        return 3;    }    public CharSequence getPageTitle(int position){        return getResources().getStringArray(R.array.tabs)[position];    }}@OverrIDepublic boolean onCreateOptionsMenu(Menu menu) {    getMenuInflater().inflate(R.menu.menu_main,menu);    return true;}@OverrIDepublic boolean onoptionsItemSelected(MenuItem item) {    int ID = item.getItemID();    if (ID == R.ID.action_settings) {        Toast.makeText(this,"hey you just hit " + item.getTitle(),Toast.LENGTH_LONG).show();        return true;    }    if (ID == R.ID.action_next) {        startActivity(new Intent(this,DetailActivity.class));    }    return super.onoptionsItemSelected(item);}

}

FragmentAll.java(其他2个片段与FragmentAll类似.)

公共类FragmentAll扩展Fragment {

private static final String ARG_ParaM1 = "param1";private static final String ARG_ParaM2 = "param2";private String mParam1;private String mParam2;public static FragmentAll newInstance(String param1,String param2) {    FragmentAll fragment = new FragmentAll();    Bundle args = new Bundle();    args.putString(ARG_ParaM1,param1);    args.putString(ARG_ParaM2,param2);    fragment.setArguments(args);    return fragment;}public FragmentAll() {    // required empty public constructor}@OverrIDepublic voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    if (getArguments() != null) {        mParam1 = getArguments().getString(ARG_ParaM1);        mParam2 = getArguments().getString(ARG_ParaM2);    }}@OverrIDepublic VIEw onCreateVIEw(LayoutInflater inflater,VIEwGroup container,Bundle savedInstanceState) {    // Inflate the layout for this fragment    return inflater.inflate(R.layout.fragment_all,container,false);}}

堆栈跟踪：

androID.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference            at androID.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:116)            at androID.support.v4.vIEw.VIEwPager.addNewItem(VIEwPager.java:836)            at androID.support.v4.vIEw.VIEwPager.populate(VIEwPager.java:986)            at androID.support.v4.vIEw.VIEwPager.populate(VIEwPager.java:918)            at androID.support.v4.vIEw.VIEwPager.onMeasure(VIEwPager.java:1440)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.linearLayout.measureChildBeforeLayout(linearLayout.java:1436)            at androID.Widget.linearLayout.measureVertical(linearLayout.java:722)            at androID.Widget.linearLayout.onMeasure(linearLayout.java:613)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.FrameLayout.onMeasure(FrameLayout.java:430)            at androID.support.v7.internal.Widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.linearLayout.measureChildBeforeLayout(linearLayout.java:1436)            at androID.Widget.linearLayout.measureVertical(linearLayout.java:722)            at androID.Widget.linearLayout.onMeasure(linearLayout.java:613)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.FrameLayout.onMeasure(FrameLayout.java:430)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.linearLayout.measureChildBeforeLayout(linearLayout.java:1436)            at androID.Widget.linearLayout.measureVertical(linearLayout.java:722)            at androID.Widget.linearLayout.onMeasure(linearLayout.java:613)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwGroup.measureChilDWithmargins(VIEwGroup.java:5463)            at androID.Widget.FrameLayout.onMeasure(FrameLayout.java:430)            at com.androID.internal.policy.impl.PhoneWindow$DecorVIEw.onMeasure(PhoneWindow.java:2560)            at androID.vIEw.VIEw.measure(VIEw.java:17430)            at androID.vIEw.VIEwRootImpl.performMeasure(VIEwRootImpl.java:2001)            at androID.vIEw.VIEwRootImpl.measureHIErarchy(VIEwRootImpl.java:1166)            at androID.vIEw.VIEwRootImpl.performTraversals(VIEwRootImpl.java:1372)            at androID.vIEw.VIEwRootImpl.doTraversal(VIEwRootImpl.java:1054)            at androID.vIEw.VIEwRootImpl$TraversalRunnable.run(VIEwRootImpl.java:5779)            at androID.vIEw.Choreographer$CallbackRecord.run(Choreographer.java:767)            at androID.vIEw.Choreographer.doCallbacks(Choreographer.java:580)            at androID.vIEw.Choreographer.doFrame(Choreographer.java:550)            at androID.vIEw.Choreographer$FramedisplayEventReceiver.run(Choreographer.java:753)            at androID.os.Handler.handleCallback(Handler.java:739)            at androID.os.Handler.dispatchMessage(Handler.java:95)            at androID.os.Looper.loop(Looper.java:135)            at androID.app.ActivityThread.main(ActivityThread.java:5221)            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:899)            at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:694)

解决方法

public static final int SERVICES_ALL = 1;public static final int SERVICES_FEATURED = 2;public static final int SERVICES_NEW = 3;

应该

public static final int SERVICES_ALL = 0;public static final int SERVICES_FEATURED = 1;public static final int SERVICES_NEW = 2;

getItem是从0开始的索引,这意味着在你的代码中,你的Adapter的case 0永远不会匹配一个,在这种情况下你返回一个null片段导致异常

总结

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