问题
I have an activity with bottom navigation tabs that are changing the fragments in it. When I click back and forth on those tabs, at some point it stops working. Code executes just fine as I put some logs in it. But the fragments aren't being switched.
Code is in kotlin but it's rather straight forward
fun showTabFragment(tag: String) {
val currentFragment: Fragment? = supportFragmentManager.fragments?.lastOrNull()
var fragment = supportFragmentManager.findFragmentByTag(tag)
val fragmentExists = fragment != null
if (fragment == null) {
when (tag) {
TAG_LOGBOOK -> fragment = LogbookFragment()
TAG_RECIPES -> fragment = RecipesFragment()
TAG_PROFILE -> fragment = ProfileFragment()
else -> fragment = MeetingPlacesFragment()
}
}
val transaction = supportFragmentManager.beginTransaction()
if (currentFragment != null) {
Log.i("jacek", "hiding " + currentFragment.javaClass.simpleName)
transaction.hide(currentFragment)
}
if (fragmentExists) {
Log.i("jacek", "showing " + fragment.javaClass.simpleName)
transaction.show(fragment)
} else {
Log.i("jacek", "adding " + fragment.javaClass.simpleName)
transaction.add(R.id.container, fragment, tag)
}
transaction.commit()
}
The fragments are quite heavy. I will try with some lightweight ones, but still that shouldn't be a problem in my opinion. Is there anything else I could try?
I'm using the latest support library - 25.2.0 Also I'm not interested in replacing the fragments as the point is to add crossfade animation without recreating them
回答1:
You need to reuse the same instance of a fragment that you wanted to hide or show.
private fun replaceFragment(fragment: Fragment) {
supportFragmentManager.beginTransaction().apply {
if (fragment.isAdded) {
show(fragment)
} else {
add(R.id.fmFragmentContainer, fragment)
}
supportFragmentManager.fragments.forEach {
if (it != fragment && it.isAdded) {
hide(it)
}
}
}.commit()
}
回答2:
@Ali's answer is good, yet imagine if you have 5 fragments. This is another way to show/hide your fragments:
// in BaseFragment
public abstract String getTAG();
//in FragmentA, FragmentB and FragmentC
public String getTAG(){
return TAG;
}
//Activity containing the fragments
//android.support.v4.app.Fragment;
private FragmentA fragmentA; //inherited BaseFragment
private FragmentB fragmentB; //inherited BaseFragment
private FragmentC fragmentC; //inherited BaseFragment
private ConcurrentHashMap<String,BaseFragment> mapOfAddedFragments = new ConcurrentHashMap<>();
/**
* Displays fragment A
*/
private void displayFragmentA() {
displayFragment(fragmentA)
}
/**
* Displays fragment B
*/
private void displayFragmentB() {
displayFragment(fragmentB)
}
/**
* Displays fragment C
*/
private void displayFragmentC() {
displayFragment(fragmentC)
}
/**
* Loads a fragment using show a fragment
* @param fragment
*/
private void displayFragment(BaseFragment fragment){
if(!mapOfAddedFragments.containsKey(fragment.getTAG()))
mapOfAddedFragments.put(fragment.getTAG(), fragment);
showFragment(fragment.getTAG(), R.id.containerBody);
}
/**
* Displays a fragment and hides all the other ones
* @param fragmentTag is the tag of the fragment we want to display
*/
private void showFragment(String fragmentTag, @IdRes int containerViewId){
FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
BaseFragment fragment = null;
fragment = mapOfAddedFragments.get(fragmentTag);
if(fragment != null) {
if (fragment.isAdded())
ft.show(fragment);
else { //fragment needs to be added to the frame container
ft.add(containerViewId, fragment, fragment.getTAG());
}
}
else //the chosen fragment doesn't exist
return;
//we hide the other fragments
for (ConcurrentHashMap.Entry<String, BaseFragment> entry : mapOfAddedFragments.entrySet()){
if(!entry.getKey().equals(fragmentTag)){
BaseFragment fragmentTemp = entry.getValue();
// Hide the other fragments
if(fragmentTemp != null)
if(fragmentTemp.isAdded())
ft.hide(fragmentTemp);
}
}
//commit changes
ft.commit();
}
And to instantiate them you can do this in the onCreate() method of your activity:
//don't forget to get the .TAG elsewhere before using them here
//never call them directly
private void instantiateFragments(Bundle inState) {
if (inState != null) {
fragmentA = inState.containsKey(FragmentA.TAG) ?
(FragmentA) getSupportFragmentManager().getFragment(inState, FragmentA.TAG):
FragmentA.newInstance(FragmentA.TAG,"0");
fragmentB = inState.containsKey(FragmentB.TAG) ?
(FragmentB) getSupportFragmentManager().getFragment(inState, FragmentB.TAG):
FragmentB.newInstance(FragmentB.TAG,"1");
fragmentc = inState.containsKey(FragmentC.TAG) ?
(FragmentC) getSupportFragmentManager().getFragment(inState, FragmentC.TAG):
FragmentC.newInstance(FragmentC.TAG,"2");
}
else{
fragmentA = FragmentA.newInstance(FragmentA.TAG,"0");
fragmentB = FragmentB.newInstance(FragmentB.TAG,"1");
fragmentc = FragmentC.newInstance(FragmentC.TAG,"2");
}
}
Edit according to Shujaat Ali Khan's question:
The BaseFragment extends support4 fragment:
public abstract class BaseFragment extends Fragment {
public abstract String getTAG();
//whatever we can add to be inherited
}
FragmentA for example:
public class FragmentA extends BaseFragment {
// Store instance variables
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private String mParam1;
private String mParam2;
public static final String TAG = "FragmentA";
// newInstance constructor for creating fragment with arguments
public static FragmentA newInstance(String param1, String param2) {
FragmentA fragment = new FragmentA();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
// Store instance variables based on arguments passed
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
// Inflate the view for the fragment based on layout XML
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragmentA, container, false);
return view;
}
//other lifecycle methods
@Override
public String getTAG() {
return TAG;
}
}
Finally the R.id.containerBody is the id of a FrameLayout containing the fragments in the activity containing these fragments.
回答3:
The problem here is even though you're hiding "current" fragment, there are other fragments loaded in the memory and that gives inconsistent behaviour.
You should be able to fix this by hiding all the fragment except the fragment you want to show.
Thanks to this answer. Show hide fragment in android
eg:
private FragmentA fragmentA;
private FragmentB fragmentB;
private FragmentC fragmentC;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentA = FragmentA.newInstance();
fragmentB = FragmentB.newInstance();
fragmentC = FragmentC.newInstance();
}
protected void displayFragmentA() {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
if (fragmentA.isAdded()) {
ft.show(fragmentA);
} else {
ft.add(R.id.fragement_container, fragmentA);
}
if (fragmentB.isAdded()) { ft.hide(fragmentB); }
if (fragmentC.isAdded()) { ft.hide(fragmentC); }
ft.commit();
}
Similarly you will have to write functions for displayFragmentB() and displayFragmentC()
来源：https://stackoverflow.com/questions/42795611/fragmenttransaction-hide-show-doesnt-work-sometimes