public class NewFrag extends Fragment{
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);
setHasOptionsMenu(true);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.newfrag, container, false);
}
}
public class PrimaryFragment extends Fragment {
Button btn1;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.primary, container, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
btn1 = (Button)view.findViewById(R.id.btn1);
btn1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Fragment var1 = new NewFrag();
((MainActivity)getActivity()).replaceFragment(var1);
}
});
}
}public class TabFragment extends Fragment {
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 2 ;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.tab_layout, container, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
tabLayout = (TabLayout) view.findViewById(R.id.tabs);
viewPager = (ViewPager) view.findViewById(R.id.viewpager);
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
}
class MyAdapter extends FragmentPagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
}
/**
* Return fragment with respect to Position .
*/
@Override
public Fragment getItem(int position)
{
switch (position){
case 0 : return new PrimaryFragment();
case 1 : return new SocialFragment();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
/**
* This method returns the title of the tab according to the position.
*/
@Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0 :
return "Primary";
case 1 :
return "Social";
}
return null;
}
}
}public class MainActivity extends AppCompatActivity{
DrawerLayout mDrawerLayout;
NavigationView mNavigationView;
ActionBarDrawerToggle mDrawerToggle;
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/**
*Setup the DrawerLayout and NavigationView
*/
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
mNavigationView = (NavigationView) findViewById(R.id.shitstuff) ;
/**
* Lets inflate the very first fragment
* Here , we are inflating the TabFragment as the first Fragment
*/
mFragmentManager = getSupportFragmentManager();
mFragmentTransaction = mFragmentManager.beginTransaction();
mFragmentTransaction.replace(R.id.containerView,new TabFragment()).addToBackStack(null).commit();
/**
* Setup click events on the Navigation View Items.
*/
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
mDrawerLayout.closeDrawers();
if (menuItem.getItemId() == R.id.nav_item_inbox) {
FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.containerView,new NavOne()).addToBackStack(null).commit();
}
if (menuItem.getItemId() == R.id.nav_item_sent) {
FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
xfragmentTransaction.replace(R.id.containerView,new NavTwo()).addToBackStack(null).commit();
}
return false;
}
});
/**
* Setup Drawer Toggle of the Toolbar
*/
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, toolbar,R.string.app_name,
R.string.app_name);
mDrawerLayout.setDrawerListener(mDrawerToggle);
mDrawerToggle.syncState();
}
public void replaceFragment(Fragment fragment){
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.replace(R.id.containerView, fragment).addToBackStack(null);
t.commit();
}
public void showArrow(){
mDrawerToggle.setDrawerIndicatorEnabled(false);
//getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
onBackPressed();
break;
default:
break;
}
return super.onOptionsItemSelected(item);
}
}
这个主题可能看起来很旧，可能会有很多答案，但我的情况非常独特。我必须在MainActivity中实现Navigation Drawer和TabLayout。所以我使用了这个tutorial。它在MainActivity中使用FrameLayout + Navigation并使用FrameLayout附加片段。这个片段有TabLayout。现在我在Tab的一个片段中有一个按钮，它会打开另一个片段。我想在这个新片段中显示back arrow按钮。我禁用了drawertoggle但无法显示后退按钮。但我的应用程序崩溃与NullPointerException。有没有其他方法可以显示箭头按钮并使用它来转到上一个片段？
答案 0 :(得分：0)
然而，在调用commit（）之前，您可能需要调用addToBackStack（），以便将事务添加到片段事务的后台堆栈中。此后备堆栈由活动管理，并允许用户通过按“返回”按钮返回到先前的片段状态。
示例：
FragmentTransaction tx = fragmentManager.beginTransation();
tx.replace( R.id.fragment, new MyFragment() ).addToBackStack( "tag" ).commit();
我的解决方案：
主菜单xml：
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<item android:id="@+id/action_settings"
android:title="@string/action_settings"
android:orderInCategory="100"
app:showAsAction="never"/>
<item android:id="@+id/my_back_arrowID"
android:icon="@drawable/arrow_left"
android:visible="false"
app:showAsAction="ifRoom">
</item>
MainActivity：
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
Toast.makeText(MainActivity.this, "settings", Toast.LENGTH_SHORT).show();
} else if (id == R.id.my_back_arrowID) {
onBackPressed();
}
return super.onOptionsItemSelected(item);
}
您希望后箭头可见的片段：
@Override
public void onPrepareOptionsMenu(Menu menu) {
menu.findItem(R.id.my_back_arrowID).setVisible(true);
super.onPrepareOptionsMenu(menu);
}