如何在导航抽屉内添加标签？当我尝试在导航抽屉中添加选项卡时出现错误。 导航抽屉：
public class MyFitTrackNavActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
FragmentTransaction mFragmentTransaction;
android.support.v4.app.FragmentManager mFragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_fit_track_nav);
FragmentManager fm = getFragmentManager();
fm.beginTransaction().replace(R.id.content_frame,new HomeFragment()).commit();
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.my_fit_track_nav, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
FragmentManager fm = getFragmentManager();
int id = item.getItemId();
switch (id) {
case R.id.action_settings:
fm.beginTransaction().replace(R.id.content_frame,new SettingFragment()).commit();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
FragmentManager fm = getFragmentManager();
int id = item.getItemId();
if (id == R.id.nav_home)
{
fm.beginTransaction().replace(R.id.content_frame,new HomeFragment()).commit();
}
else if (id == R.id.nav_weight)
{
FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
xfragmentTransaction.replace(R.id.content_tab, new WeightFragment()).commit();
}
else if (id == R.id.nav_logout)
{
fm.beginTransaction().replace(R.id.content_frame,new LogoutFragment()).commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
item.setChecked(true);
setTitle(item.getTitle());
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
标签：
public class WeightFragment extends Fragment {
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 3 ;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_tab_control, container, false);
tabLayout = (TabLayout)rootView.findViewById(R.id.tablayout);
viewPager = (ViewPager)rootView.findViewById(R.id.viewpager);
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
return rootView;
}
class MyAdapter extends FragmentPagerAdapter{
public MyAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position)
{
switch (position){
case 0 : return new KeyInWeightF();
case 1 : return new HistoryF();
case 2 : return new AnalysisF();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0 :
return "Weight";
case 1 :
return "History";
case 2 :
return "Analysis";
}
return null;
}
}
这是选项卡中的选项卡片段（WeightFragment）
public class KeyInWeightF extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.daily_weight_fragement,null);
}
}
这是我的标签设计：
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
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"
android:fitsSystemWindows="true"
tools:context="com.example.sam.myfittrack.Tabs.WeightFragment">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.design.widget.TabLayout
android:id="@+id/tablayout"
android:layout_width="match_parent"
android:layout_height="19dp"
app:tabMode="fixed"
app:tabGravity="fill"
android:layout_below="@+id/toolbar"/>
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:layout_below="@+id/tablayout"/>
</android.support.design.widget.CoordinatorLayout>
错误：
java.lang.NullPointerException
at com.example.sam.myfittrack.MyFitTrackNavActivity.onNavigationItemSelected(MyFitTrackNavActivity.java:118)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:150)
at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:153)
at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:300)
at android.view.View.performClick(View.java:4336)
at android.view.View$PerformClick.run(View.java:17826)
at android.os.Handler.handleCallback(Handler.java:800)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5434)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:852)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:619)
at dalvik.system.NativeStart.main(Native Method)