问题
Whats the proper way to handle the selected state of the navigation drawer after back press?
I have a navigation drawer with n entries (in a listview) like the SDK sample in Android Studio. When i click on the navigation drawer entries i want them to be added to the back stack, so i can move back to them.
In onNavigationDrawerItemSelected(int pos) i have
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
if (position == 0) {
transaction.replace(R.id.container, new FragmentA());
} else if (position == 1) {
transaction.replace(R.id.container, new FragmentB());
} else {
transaction.replace(R.id.container, new FragmentC());
}
transaction.addToBackStack(null);
transaction.commit();
When i click on the second entry in the drawer, B gets selected and replaces A. If i click the back button afterwards, Fragment A is shown again like it should, but B is still selected in the navigation drawer.
How can i get the selection status of the drawer updated after pressing back?
Somehow i need a call to mDrawerListView.setItemChecked(position, true); or NavigationDrawerFragment.selectItem(int position). But to which position? How do i remeber it?
Intercept with onBackPressed?
@Override
public void onBackPressed() {}
But how do i know which fragment is active again? And to which position it corresponds.
Is there some easy solution i am blind to see? It seems that using back in combination with the navigation drawer and updating the selection status is a standard pattern.
回答1:
This pattern is described in the Implement Back Navigation for Fragments section of the "Proper Back Navigation" documentation.
If your application updates other user interface elements to reflect the current state of your fragments, such as the action bar, remember to update the UI when you commit the transaction. You should update your user interface after the back stack changes in addition to when you commit the transaction. You can listen for when a
FragmentTransactionis reverted by setting up aFragmentManager.OnBackStackChangedListener:
getSupportFragmentManager().addOnBackStackChangedListener(
new FragmentManager.OnBackStackChangedListener() {
public void onBackStackChanged() {
// Update your UI here.
}
});
That would be the proper place to refresh the current option in the navigation drawer.
回答2:
today I had the same strugle. I solved it by implementing an Interface FragmentToActivity in every Fragment and in my one and only MainActivity.
Interface:
public interface FragmentToActivity {
public void SetNavState(int id);
}
Fragments:
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
((FragmentToActivity) getActivity()).SetNavState(R.id.nav_myitemid); //just add this line
}
MainActivity:
@Override
public void SetNavState(int id) {
NavigationView nav = (NavigationView) findViewById(R.id.nav_view);
nav.setCheckedItem(id);
}
And if you have no idea, where R.id.nav_myitemid comes from, here is my activity_main_drawer.xml:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<group android:checkableBehavior="single">
<item
android:id="@+id/nav_myitemid"
android:title="@string/home" />
</group>
</menu>
回答3:
I have had alot of trouble trying to figure out a solution to this problem and the solution I ended up using isn't "nice" in my opinion, but it works.
In my application i ended up adding a fragments position in the navigation drawer, when i added the fragment to the backstack. This way i could call setItemChecked with the position in my onBackStackChanged(). So basicly what i did was this:
@Override
public void onBackStackChanged() {
FragmentManager fm = getFragmentManager();
String name = fm.getBackStackEntryAt(fm.getBackStackEntryCount()-1).getName();
mDrawerList.setItemChecked(Integer.parseInt(name),true);
}
public class DrawerItemClickListener implements android.widget.AdapterView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectItem(position);
}
}
private void selectItem(int position) {
Fragment fragment;
switch (position) {
case 0: // Home
fragment = new ContentFragment();
break;
case 1: // Another
fragment = new AnotherFragment();
break;
default: // Logout
{
finish();
Intent intent = new Intent(this, StartupActivity.class);
startActivity(intent);
return;
}
}
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragment)
.addToBackStack(Integer.toString(position))
.commit();
mDrawerList.setItemChecked(position, true);
setTitle(mNavigationItems[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
回答4:
Building upon @matiash 's excellent answer (be sure to +1 his/hers if you +1 my answer)
To start, we're assuming we're in the Activity
getFragmentManager().addOnBackStackChangedListener(
new FragmentManager.OnBackStackChangedListener() {
public void onBackStackChanged() {
// Update your UI here.
}
});
You can find the current fragment with the following:
(from https://stackoverflow.com/a/24589081/878159)
Fragment f = getFragmentManager().findFragmentById(R.id.frag_container);
if (f instanceof CustomFragmentClass) {
// do something with f
f.doSomething();
}
That should get you a step closer. Then something like this will get you a reference to your nav drawer:
nav = (NavigationDrawerFragment) getFragmentManager().findFragmentById(R.id.nav);
Then depending how you setup your drawer fragment code:
nav.updateSelected(position);
The updateSelected(int) method would be in your NavigationDrawerFragment class and might look something like this:
public void updateSelected(int position) {
mCurrentSelectedPosition = position;
if (mDrawerListView != null) {
mDrawerListView.setItemChecked(position, true);
}
}
NOTE: there are many ways to do this, but this should get you started.
回答5:
This is late but for those who are using navigation menu instead of list, here is how i did it
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int position=0;
Fragment fragment;
int id = item.getItemId();
if (id == R.id.nav_home) {
fragment=new HomeFragment();
position=0;
} else if (id == R.id.nav_profile) {
fragment=new ProfileFragment();
position=1;
} else if (id == R.id.nav_settings) {
fragment=new SettingsFragment();
position=2;
}
getSupportFragmentManager()
.beginTransaction()
.add(R.id.relative_container, fragment)
.addToBackStack(""+position)
.commit();
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
and add listner for backstack
getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
FragmentManager fm = getSupportFragmentManager();
String name = fm.getBackStackEntryAt(fm.getBackStackEntryCount()-1).getName();
if(!TextUtils.isEmpty(name))
selectNavigationDrawerItem(Integer.parseInt(name));
}
});
selectNavigationDrawerItem method
private void selectNavigationDrawerItem(int position){
if(position==0){
navigationView.setCheckedItem(R.id.nav_home);
}
else if(position==1){
navigationView.setCheckedItem(R.id.nav_profile);
}
else if(position==2){
navigationView.setCheckedItem(R.id.nav_settings);
}
}
来源：https://stackoverflow.com/questions/27824642/update-selected-state-of-navigation-drawer-after-back-press