问题
I have an Activity that contains a BottomNavigationView, and this bottomnav helps the activity to display three fragments. These fragments load well, and I use an AsyncTask to do every heavy operation, while in the UI thread, I show a ProgressBar until everything loads.
There is a weird behaviour with my fragment: The first time I load the fragment it takes some time to actually display it, instead of displaying it instantly with a progressbar.
This thing only happens the first time, and only in this fragment.
The fragment code only contains this:
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
new LoadData(getView(), getContext()).execute();
}
private class LoadData extends AsyncTask<Void, Void, Void> {
private View v;
private Context context;
public LoadData(View v, Context context) {
items = new ArrayList<>();
this.v = v;
this.context = context;
}
@Override
protected Void doInBackground(Void... voids) {
setItems(context); //Heavy operation
adapter = new DashAdapter(items, context);
return null;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
//shows progressbar
progress = v.findViewById(R.id.DFProgress);
progress.setVisibility(View.VISIBLE);
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
setPager();
//sets viewPager and hides progressbar
progress.setVisibility(View.GONE);
}
}
In the gif below, if you look at the bottomnavigationview at the bottom, you can see that it takes time to display the fragment. But after trying to load the fragment a second time, it loads as expected.
How could I make the fragment to load the right way?
回答1:
I had the same problem. I have two options.
- Use postdelay when you call LoadData or
- First add all fragments with manually. You manage navigationItemSelected yourself.
Like this:
val firstFragment: Fragment = FirstFragment()
val secondFragment: Fragment = SecondFragment()
val thirdFragment: Fragment = ThirdFragment()
val navView: BottomNavigationView = findViewById(R.id.nav_view)
var active = firstFragment
fm.beginTransaction().add(R.id.nav_host_fragment, thirdFragment, "3").hide(thirdFragment).commit()
fm.beginTransaction().add(R.id.nav_host_fragment, secondFragment, "2").hide(secondFragment).commit()
fm.beginTransaction().add(R.id.nav_host_fragment, firstFragment, "1").commit()
navView.setOnNavigationItemReselectedListener { }
navView.setOnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_first -> {
fm.beginTransaction().hide(active).show(firstFragment).commit()
active = firstFragment
}
R.id.navigation_second -> {
fm.beginTransaction().hide(active).show(secondFragment).commit()
active = secondFragment
}
R.id.navigation_third -> {
fm.beginTransaction().hide(active).show(thirdFragment).commit()
active = thirdFragment
}
}
true
}
And remove these lines in your nav_host_fragment:
app:defaultNavHost="true"
app:navGraph="@navigation/mobile_navigation"
回答2:
you can use jetpack navigation for simple bottombar navigation
Simple Bottom Navigation with Jetpack Navigation:
Let’s start by including the Jetpack Navigation library in your apps by adding these lines in app’s build.gradle file:
def nav_version = "2.1.0"
implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
implementation "androidx.navigation:navigation-ui-ktx:$nav_version"
We start by creating a simple bottom navigation flow first. For that, you need to do first add NavHostFragment in your single activity layout file. Add this in the activity_main.xml file inside the FrameLayout tag.
<fragment
android:id="@+id/fragNavHost"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="@navigation/bottom_nav_graph" />
You will see an error saying “Cannot resolve symbol @navigation/bottom_nav_graph .”
<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/bottom_nav_graph.xml"
app:startDestination="@id/homeFragment2">
<fragment
android:id="@+id/homeFragment2"
android:name="com.wajahatkarim3.bottomnavigationdemo.HomeFragment"
android:label="fragment_home"
tools:layout="@layout/fragment_home" />
<fragment
android:id="@+id/searchFragment2"
android:name="com.wajahatkarim3.bottomnavigationdemo.SearchFragment"
android:label="fragment_search"
tools:layout="@layout/fragment_search" />
<fragment
android:id="@+id/notificationsFragment2"
android:name="com.wajahatkarim3.bottomnavigationdemo.NotificationsFragment"
android:label="fragment_notifications"
tools:layout="@layout/fragment_notifications" />
<fragment
android:id="@+id/profileFragment2"
android:name="com.wajahatkarim3.bottomnavigationdemo.ProfileFragment"
android:label="fragment_profile"
tools:layout="@layout/fragment_profile" />
</navigation>
Its time for add some code in our activity class. Open MainActivity.kt file, and create a method setupViews() in it. Call this in onCreate() of the activity. Add these lines in the setupVeiws() method.
fun setupViews()
{
// Finding the Navigation Controller
var navController = findNavController(R.id.fragNavHost)
// Setting Navigation Controller with the BottomNavigationView
bottomNavView.setupWithNavController(navController)
// Setting Up ActionBar with Navigation Controller
// Pass the IDs of top-level destinations in AppBarConfiguration
var appBarConfiguration = AppBarConfiguration(
topLevelDestinationIds = setOf (
R.id.homeFragment,
R.id.searchFragment,
R.id.notificationsFragment,
R.id.profileFragment
)
)
setupActionBarWithNavController(navController, appBarConfiguration)
}
来源：https://stackoverflow.com/questions/60403240/lag-when-switching-tabs-in-bottomnavigationview