Develop Reference

Call Main activity from a Fragment

fragment class
Home/main activity
How to limit my main activity to not go back on the last page of my Fragment once return from the last page of Fragment to Main activity like I have One Home activity and that home activity leads to 3 more activities on clicking the button and in which one activity has fragments. The last page of the fragment is leading to home activity but when I back pressed on the home activity it again leads me to the last page of a fragment from where I've come and then I press the back button again then my application shuts

When you are adding your Fragments to the FragmentManager make sure to avoid adding it to the backstack, if you don't want it to appear on its own.
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.fragment_layout,fragment);
//Adding null will stop the fragment from reappearing on a backpress.
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
In the future please post code in text format. Do not post images of code. If you need to show some view behavior on the screen then its fine to post images, but not code.

TabLayout Fragment Issue

Current layout
The above is the app layout in Android app that I am working on. There is an activity, which has a BottomNavigationView. The navigation is managed using:
this.getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment).commit();
Now, on this fragment, I have a TabLayout and a ViewPager as you can see in the image. The ViewPager listens to the TabLayout selector and it can be changed by either sliding the ViewPager or clicking on the tab. Works fine..
Once a tab is selected, I am loading another Fragment that has a RecyclerView on it. The contents in the RecyclerView is coming from a URL so its being updated on Post() as below:
CompletableFuture.runAsync(this::prepare);
recyclerView.post(() ->
{
adapter.list = newList;
adapter.notifyDataSetChanged();
progress.setVisibility(View.INVISIBLE);
});
Now the issue that I am facing:
Everything works fine for the first time when the Menu 1 in the layout image is clicked. The recycler view is able to call the service and load the content. Now if I switch the navigation to Menu 2 or any other and try to come back to Menu 1, nothing progresses from the ViewPager / TabLayout. Up to the TabLayout I can see Logs, and after that nothing. Basically setting the currentItem to the TabLayout is called but its not calling the create of the next Fragment and hence its not loading the RecyclerView again. The ViewPager is using FragmentStatePagerAdapter.
TabViewerAdapter extends FragmentStatePagerAdapter
The adapter is initialised using ChildFragmentAdapter as below:
TabViewerAdapter adapter = new TabViewerAdapter(getChildFragmentManager(), 0, tabs.getTabCount());
I know behaviour "0" is deprecated so tried with "1" as well as below:
TabViewerAdapter adapter = new TabViewerAdapter(getChildFragmentManager(), 1, tabs.getTabCount());
Tried invalidating views, notifying adapter and many other.. No use.
I also noticed that when I switch app (while its running by tapping the phone square button to go to another app) and come back (resume) then its loading the recycler view again.
This means, I am missing something and tried the onResume method. But didn't work.
Am I doing something stupid or against design patterns or conventions? No idea what to do..
Please help, thank you.

I resolved this issue by doing the things below:
Used a SharedViewModel to handle the list
Used ListAdapter for RecyclerView
All good now.

add toolbar menu only at specific fragments

So I have this app and in the toolbar, there is a drop-down menu and I am looking for a solution on how to show only specific items at specific fragments.
I know that I have to make a java class and link it to the menu, but how do I find out what fragment I am on?

You can move the implementation of setting the toolbar for your fragments in the activity that launches these fragments. In that case, you may have the toolbar in your activity and the activity should have a fragment container where you will put your fragment. Let us consider a layout like the following for your activity.
<RelativeLayout>
<!-- Your toolbar here in the activity -->
<ToolBar>
android:id="+#id/toolbar"
...
</ToolBar>
<!-- Your fragment container here -->
<FrameLayout>
android:id="+#id/fragment_container"
...
android:layout_below="#id/toolbar"
</FrameLayout>
</RelativeLayout>
Now, you have the ToolBar here in your activity and hence, you can set the toolbar when you are loading the fragments in the fragment container. Your activity might have the following functions.
public void launchFrag1() {
// replace the fragment 1 in the fragment container
loadToolbarForFrag1();
}
public void launchFrag2() {
// replace the fragment 2 in the fragment container
loadToolbarForFrag2();
}
Now call the specific function of your activity to load the fragment and the toolbar dynamically as well.
If you are trying to call the method from the fragment, you can always call those methods declared in your activity like the following.
((YourActivity) getActivity()).launchFrag2();
I hope you get the idea.
Please note that this is just a basic implementation of how you can get your dynamic toolbar working in your app. However, your implementation might vary based on the use case that you have.
I hope that helps!

I have an ImageView in the toolbar which I hide as follows:
// Show image in fragment 1
ImageView img = getActivity().findViewById(R.id.toolbarMenu);
img.setVisibility(View.VISIBLE);
// hide image in fragment 2
ImageView img = getActivity().findViewById(R.id.toolbarMenu);
img.setVisibility(View.GONE);
Try these codes in onCreateView after inflating your layout

Syntax for image button

How do I make the image button change to different fragment on click?
On the homepage fragment I have an image button. How do I code it so that it changes to a different fragment when clicked. Note that I have java classes for all my fragments as well as the main activity class.
Where would I put the code for this image button and how would I do it because everything I have tried doesn't work.

You can create onClickListener for the image button in home fragment and inside onclick:
Fragment fragment = new {your-fragment()};
FragmentManager fm1 = getActivity().getSupportFragmentManager();
FragmentTransaction ft1 = fm1.beginTransaction();
fm1.popBackStack();
ft1.replace({layout}, fragment).addToBackStack("tag");
ft1.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft1.commit();
Hope this helps

Android: add two or more fragments to the same backstack state

I have a main activity with a RelativeLayout container where i load different fragments using theFragmentManager.
Let's say i load fragment1 and fragment2 with two transactions. In case of back button pressed, i want to return to the state when both fragment1 and fragment2 were not loaded. Is this possible?
I've tried to use the same name in the addToBackStack() method:
mFragmentManager.beginTransaction().replace(R.id.activity_main, fragment1).addToBackStack("SameState").commit();
mFragmentManager.beginTransaction().add(R.id.activity_main, fragment2).addToBackStack("SameState").commit();
but this doesn't work. If i press the back button fragment2 disappears first, then pressing again fragment1 goes away too. Any suggestion?

Try this:
mFragmentManager.beginTransaction()
.replace(R.id.activity_main,fragment1)
.addToBackStack(null)
.commit();
getSupportFragmentManager().popBackStack(); // Pop the first transaction
mFragmentManager.beginTransaction()
.replace(R.id.activity_main,fragment2)
.addToBackStack(null)
.commit();
At this point, when you press the back button, it will simply revert the last transaction (fragment2 replacing).