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How can i access the find view by id of bottom nav outside on create in android

I am working on an application where I am using bottom navigation on Home where i have three fragments on the second fragment called Post Ad I have a button called enter fragment zone through that i enter into another fragment now when I enter inside another fragment now I don't want there to show the bottom navigation so to hide it I am using a method inside my main activity called "setBottomNavigationVisibility" where I am writing code to set the visibility of bottom nav. but the problem is that it is throwing the null pointer exception in the mainactivty's method saying that
"void com.google.android.material.bottomnavigation.BottomNavigationView.setVisibility(int)' on a null object reference" on the method's line where i am setting the visibility
code of MainActivity
public class MainActivity extends AppCompatActivity {
NavController navController;
BottomNavigationView bottomNavigationView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
navController = Navigation.findNavController(this, R.id.fragmentContainerView);
bottomNavigationView = findViewById(R.id.activity_main_bottom_navigation_view);
NavigationUI.setupWithNavController(bottomNavigationView, navController);
}
public void setBottomNavigationVisibility(int visibility) {
bottomNavigationView.setVisibility(visibility);
}}
On the above method when i am trying to setting the visibility on the line bottomNavigationView.setVisibility(visibility); that's where it is thrwoing the exception
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
binding = FragmentSecondBinding.inflate(inflater, container, false);
// Inflate the layout for this fragment
View view = binding.getRoot();
viewModel = new ViewModelProvider(requireActivity()).get(PageViewModel.class);
((MainActivity) requireActivity()).setBottomNavigationVisibility(View.GONE);
binding.toolbar.setNavigationOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Navigation.findNavController(view).navigate(R.id.action_secondFragment2_to_postad);
}
});
No Please guide me how can i solve this error.

do something like this, define interface
interface DashboardActivityDelegate {
void hideBottomBar();
void showBottomBar();
}
your activity must implement this interface
and in your fragment in which you want to hide bottom nav view do this:
declare global variable
private DashboardActivityDelegate dashboardActivityDelegate;
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof DashboardActivityDelegate) {
dashboardActivityDelegate = (DashboardActivityDelegate)context;
}
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (dashboardActivityDelegate != null) {
dashboardActivityDelegate.hideBottomBar();
}
}
#Override
public void onDestroy() {
super.onDestroy();
if (dashboardActivityDelegate != null) {
dashboardActivityDelegate.showBottomBar();
}
}

in fragment you want hide bottom bar, just call this line in onViewCreated
getActivity().findViewById(R.id.activity_main_bottom_navigation_view).setVisibility(View.GONE);
and when you leave fragment, call this line in onDestroy or onStop to visible bottom nav for another fragment:
getActivity().findViewById(R.id.activity_main_bottom_navigation_view).setVisibility(View.VISIBLE)

Change BottomNavigationView with a button inside a RecyclerView Item

The application has a BottomNavigationView for navigating between fragments. One of the Fragments related to the BottomNavigationView has a Fragment as a child containing a RecyclerView and each RecyclerView Item has a Button attached to it.
I would need to navigate the BottomNavigationView to another Fragment with an OnClick of the Button (Highlighted with the red) inside the RecyclerView Item. I have tried different ways but I have not gotten it to work so far.
The Click is handled inside the Adapter of the RecyclerView. (The code inside the OnClickListener is just to clarify what I am trying to do.)
#Override
public void onBindViewHolder(#NonNull LocationsViewHolder holder, int position) {
...
holder.showMarkerButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
BottomNavigationView navigation = (BottomNavigationView)v.findViewById(R.id.nav_view);
navigation.setSelectedItemId(R.id.navigation_map);
}
});
}

The easiest way is created an interface implemented by your Activity
First create an interface that i called OnItemClick :
public interface OnItemClick{
void onItemClick();
}
Following on your activity implement this interface like below :
public class MainActivity extends AppCompatActivity implements OnItemClick{
/*
rest of your code
*/
#Override
public void onItemClick() {
navigation.setSelectedItemId(R.id.navigation_map);
}
}
On your Fragment you need to pass the Activity into your Adapter
YourAdapter adapter = new YourAdapter(requireActivity());
And on your adapter you need to initialize the interface like below :
OnItemClick listener;
public YourAdapter(Activity activity) {
listener= ((MainActivity) activity);
}
And finaly to call the method on your activity just call it like below
#Override
public void onBindViewHolder(#NonNull LocationsViewHolder holder, int position) {
...
holder.showMarkerButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
listener.onItemClick();
}
});
}

Access method from Dialog to MainActivity

I have a main Activity in which I created a ViewPager that instantiate 3 other Fragments. One of these is a GridView which makes a popup appear when the user click on one item. Then, in this popup, I have a simple button.
What I want to do is: when the user click on this button, I would like to access a method in my main Activity (that should change the current item of my ViewPager) and then dismiss the popup.
I tried everything I could, but I cannot achieve this... I can set up the click event on my popup and dismiss it easily, but I didn't find out how I can access a method (or even a variable) from my popup to my main Activity.
I will put my most relevant code in here so you can understand the structure of my classes (hopefully...).
My main Activity:
public class MainActivity extends FirstActivity{
private ViewPager mViewPager;
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mViewPager = (ViewPager) findViewById(R.id.viewpager);
// Set an Adapter on the ViewPager
mViewPager.setAdapter(new MainActivity_Adapter(getSupportFragmentManager()));
public void onSaveInstanceState(Bundle savedInstanceState)
{
menuBar.onSaveInstanceState(savedInstanceState);
}}
My ViewPager activity:
public class MainActivity_Adapter extends FragmentPagerAdapter{
public MainActivity_Adapter(FragmentManager fm)
{
super(fm);
}
#Override
public Fragment getItem(int position)
{
// Set the color background for each page
switch (position)
{
case 0:
return MainActivity_Inventory.newInstance();
case 1:
return MainActivity_Map.newInstance();
default:
return MainActivity_AR.newInstance();
}
}
// The number of Splash Screens to display
#Override
public int getCount()
{
return 3;
}}
My "Inventory" Fragment
public class MainActivity_Inventory extends Fragment implements View.OnClickListener{
public static MainActivity_Inventory newInstance()
{
MainActivity_Inventory frag = new MainActivity_Inventory();
Bundle b = new Bundle();
frag.setArguments(b);
return frag;
}
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
// Select the layout
int layout;
layout = R.layout.activity_inventory_01;
// Inflate the layout resource file
View view = getActivity().getLayoutInflater().inflate(layout, container, false);
// Set the grid view
GridView gridview = (GridView) view.findViewById(R.id.inventory_gridView);
gridview.setAdapter(new InventoryImageAdapter(super.getActivity()));
gridview.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
public void onItemClick(AdapterView parent, View v, int position, long id)
{
// Create a popup to show item details
createPopup();
}
});
return view;
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState)
{
super.onViewCreated(view, savedInstanceState);
}
public void createPopup()
{
DialogFragment newFragment = new PopupActivity_Inventory();
newFragment.show(getFragmentManager(), "itemDetails");
}
#Override
public void onClick(View v)
{
}}
And my popup dialog fragment:
public class PopupActivity_Inventory extends DialogFragment{
#Override
public Dialog onCreateDialog(final Bundle savedInstanceState)
{
// Build the alert dialog
final Dialog dialog = new Dialog(this.getActivity());
// Get the layout inflater
final LayoutInflater inflater = getActivity().getLayoutInflater();
// Set up the dialog box
dialog.setContentView(inflater.inflate(R.layout.activity_inventory_popup_01, null));
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
dialog.getWindow().setGravity(Gravity.TOP);
//dialog.getWindow().getAttributes().y = 100;
(dialog.findViewById(R.id.brick_button_01)).setOnClickListener(new View.OnClickListener()
{
public void onClick(View view)
{
// When button is clicked, ACCESS MAIN ACTIVITY!
dialog.dismiss();
}
});
return dialog;
}}
I really hope you can help me with this... I really need to get it working. Thank you very much!
If you need further details or explanation, please just tell me.

The best thing to do is use EventBus library. I have a demo app in which you can add items to RecyclerView from anywhere within the app using EventBus. You can use it as a reference to simply do something else instead of current task. Here is the link to the repo:
https://github.com/code-crusher/android-demos/tree/master/EventBusDemo
And if you want to understand how it works you can refer to my article, it explains how to make communications like this easy:
https://medium.com/#code_crusher/eventbus-for-android
Hope it helps. Happy coding :)

Read this https://developer.android.com/training/basics/fragments/communicating.html
Look for "To allow a Fragment to communicate up to its Activity, you can define an interface in the Fragment class and implement it within the Activity...."
Another way to achieve it is using an EventBus and post events by Fragments to be caught by Activities.

Fragments get loaded every time i switch tab, need efficient method

These are the screenshots of my application,
http://i.stack.imgur.com/3GYAc.png ==> after loading the list from remote server the list is populated.
The problem for me is this,
When i move to the title Android - third tab(refer link) and switch back to java tab, the data is loading again.
How to make it load it single time and save it, so that it doesn't load every time?
The main activity is fragmentactivity which listens to tabadapter for changes in tabs.
This one is page adapter..
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int index) {
switch (index) {
case 0:
// Top Rated fragment activity
return new TopRatedFragment2();
case 1:
// Games fragment activity
return new GamesFragment();
case 2:
// Movies fragment activity
return new MoviesFragment();
}
return null;
}
This one is fragmentActivity which uses page adapter
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.messages_layout);
// Initilization
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Adding Tabs
for (String tab_name : tabs) {
actionBar.addTab(actionBar.newTab().setText(tab_name)
.setTabListener((TabListener) this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
#Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
#Override
public void onTabReselected(Tab arg0, FragmentTransaction arg1) {
// TODO Auto-generated method stub
}
#Override
public void onTabSelected(Tab arg0, FragmentTransaction arg1) {
int position = mAdapter.getItemPosition(arg0);//;findItemPosition(arg0.getPosition());
viewPager=(getCurrentFocus()).ggetFragment(arg0, null);
viewPager.setCurrentItem(arg0.getPosition());
}

According to revision 4 of the Support Package, a method was added to ViewPager which allows you to specify the number of offscreen pages to use, rather than the default which is 1.
so you can load page rightside when move.
In your case, you want to specify 2, so that when you are on the third page, the first one is not destroyed, and vice-versa.
mViewPager = (ViewPager)findViewById(R.id.pager);
mViewPager.setOffscreenPageLimit(2);
Thats it....

I assume you are creating the Fragment each time the tab is loaded like
JavaFragment java=new JavaFragment();
Try to declare it as global and create a new instance only if the object is null
like:
JavaFragment java;
Fragment getItem(int index)
{
case 0:
if(java==null){
java=new javaFragment();}
return java;
break;
case 1:...........
..............
.............
}

Where should i declare the button of different layout?

I've made a calculator apps and I'm trying to create an about page showing some information.
The OK button will be coded setContentView(originallayout.xml) to return to the calculator layout.
Where should i put these codes to declare the OK button?
private Button btnOK;
btnOK = (Button)findViewById(R.id.btnOK);
btnok.setOnClickListener(OKListener);
I tried to put these code just below where i did for the buttons at the main layout but the apps just stopped after launch.
07-18 09:39:43.290: E/AndroidRuntime(6984): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.hychentsa.calculator/com.hychentsa.calculator.CalculatorActivity}: java.lang.NullPointerException

Instead of using setContentView() to change screens, you should have separate activities. Then, in your about activity, you can simply call finish() on button click to go back to the main activity.
http://developer.android.com/reference/android/app/Activity.html#startActivity(android.content.Intent)

if your layout doesn't content the id of the button (in your case btnOK), Eclipse throws NullPointerException - it can not find it in your layout's content.
So when you set your layout (or menu), it must content the id btnOK. Check it!
Put your button initialization after setContentView(R.layout.your_about_layout_name);
Put all this code in
Button btnOK;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.about);
btnOK = (Button)findViewById(R.id.btnOK);
btnok.setOnClickListener(OKListener);
}
Update:
Look at the answer of invertigo:
It's wrong to change the layout when you click on the button.
You have to do it this way:
CalculatorActivity
public class CalculatorActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.calculator_black);
// initialization of your views stays here
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.calculator_menu, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle item selection
switch (item.getItemId()) {
case R.id.your_id_to_go_in_about_activity:
Intent intent = new Intent(CalculatorActivity.this, AboutActivity.class);
// put some extras if you need to send information from this page to the
// AboutActivity page with this code: intent.putExtra();
startActivity(intent); // with this code you go to AboutActivity
return true;
case R.id.theme:
// Do Something with the theme
return true;
default:
return super.onOptionsItemSelected(item);
}
}
Now, the place for your initialization of OKButton is in new class, lets call it
AboutActivity
here you can put my earlier code:
public class AboutActivity extends Activity{
Button btnOK;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.about);
btnOK = (Button)findViewById(R.id.btnOK);
btnok.setOnClickListener(OKListener);
}
// and the listener for your OK button have to look like this:
OnClickListener OKListener = new OnClickListener() {
#Override
public void onClick(View v) {
// Do something here if you need
finish(); // with finish() you are returning to the previous page
// which is CalculatorActivity
}
};
}