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Android - prevent to open previous fragment

guys.
This must be a silly question but i'm not managing to work this out. My scenario is: i have in my MainActivity a BottomNavigation which i navigate over three fragments. And my problem is that when the back button (from android bottom navigation toolbar) is pressed the previous fragment opens but i want the app to close. So my question is: how i manage to prevent the previous fragments to open?
PS: I know it has something to do with FragmentMananger back stack but i did not understand how to use it.
PS2: Sorry for bad english.

The fragments are on the backstack.
Edit:
Work with FragmentTransaction and use addToBackStack (null)
// Create new fragment and transaction
Fragment newFragment = new ExampleFragment();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();

Override the onBackPressed() method in your activity.
#Override
public void onBackPressed() {
finish(); //This would close the app
}
Word of caution. This would close the activity in all the cases when the user presses back. To avoid this perhaps you would like to create something like this:
#Override
public void onBackPressed() {
if(someCondition) {
finish(); //This would close the activity
}
else {
super.onBackPressed(); //Fallbacks to default Android implementation
}
}

Handle OnBackPress from Fragment

I have 3 fragments Fragment1, Fragment2 and Fragment3 and navigation is like
Fragment1->Fragment2->Fragment3
But on back press From Fragment3 go back to Fragment2 after completing some task like from Fragment2. And from Fragment1 finish this activity.
what will be the best method to do this task.

As per your question just you have to add addToBackStack() method before commit() transaction.
for example:
FirstFragment firstFragment = new FirstFragment();
getSupportFragmentManager().beginTransaction()
.replace(R.id.article_fragment, firstFragment)
.addToBackStack(null).commit();
Add second and third fragment same as above manner and just add code in onBackPressed() Override method.
for example:
#Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() > 0) {
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}

Please follow the process.
1. When you add fragment add below code to your code
fragmentTransaction.addToBackStack(null);
Then back button handle from the activity.
#Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount()>0){
getFragmentManager().popBackStack();
}else {
super.onBackPressed();
} }
It will be working perfectly. Happy coding.

There is no need to handle OnBackPress inside Fragment. When you performing Fragment transaction, you can put your fragment to BackStack:
When there are FragmentTransaction objects on the back stack and the user presses the Back button, the FragmentManager pops the most recent transaction off the back stack and performs the reverse action (such as removing a fragment if the transaction added it).
More details you can get from this article.

How to avoid Fragment going back to previous Fragment on pressing device back button?

I am developing an android in which when I pressed device back button I go to previous fragment. What I want to achieve is that when I pressed device back button I don't want to go to previous fragment. How can I achieve that?.

You must be doing calling addtobackstack("name") while adding or replacing the fragment.Remove this function before calling next fragment you wont go back to previous fragment for further desc

Do not add that fragment to backstack of the new fragment you're calling. Look at the below example I've used to explain you how this works.
To make that fragment come again, just add that fragment to backstack which you want to come on back pressed,
Eg:
btnSignIn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Fragment fragment = new LoginFragment();
//replacing the fragment
if (fragment != null) {
FragmentTransaction ft = ((FragmentActivity)getContext()).getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, fragment);
ft.addToBackStack("SignupFragment");
ft.commit();
}
}
});
In the above case, I m opening a LoginFragment when signIn button is pressed, right now am in SignupFragment. So if I call addToBackStack(TAG), TAG = "SignupFragment", then when back button is pressed in LoginFragment, we come to SignUpFragment.
Happy Coding!

go back from fragment to previous activity onclick back button

how to go back from fragment to previous activity ?
I can't override this function in the fragment or there is other way, HELP!
#Override
public void onBackPressed() {
onBackPressed();
}

Somewhere in your code you likely have a FragmentTransaction where you are calling add() or replace() or show() to display the fragment. In between the display method and commit(), if you call addToBackStack(), then the operation is added to the back stack, so when you press the back button it reverses your fragment transaction.

Back from fragment to Activity onBackPressed

My question is that, i've one activity and one fragment,from activity open that fragment but when i pressed back button it close application.
i try with this code.
for open fragment.
case R.id.button_contact:
Fragment fragment = new FragmentContact();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame_container,fragment).addToBackStack("Frag1").commit();
break;
for back button.
#Override
public void onBackPressed() {
getSupportFragmentManager().popBackStackImmediate("Frag1",0);
super.onBackPressed();
}

I'm assuming you just want to remove the fragment and have the activity remain?
In that case modify your onBackPressed method to be
#Override
public void onBackPressed() {
if (getSupportFragmentManager().findFragmentByTag("Frag1") != null) {
getSupportFragmentManager().popBackStackImmediate("Frag1",0);
} else {
super.onBackPressed();
}
}
This will remove the fragment from the activity if it is added and if it isn't, then the back button will act as normal and destroy the activity.

Just remove this line from onBackPressed().
getSupportFragmentManager().popBackStackImmediate("Frag1",0);
Its work.

You can do something like this. It will work with your stack:
if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
super.onBackPressed();
} else {
getSupportFragmentManager().popBackStack();
}
This piece of code will pop the stack if there is any fragment. Otherwise the back button will close the activity

What these two lines are doing:
1). getSupportFragmentManager().popBackStackImmediate("Frag1",0);
As you are adding you fragment in activity backstack, so when you are calling on back press,
it remove fragment from stack, now in your stack activity is left, means stack size is one.
2). super.onBackPressed();
I think you are aware of calling super.onbackpress funcionality, here it will finish
your activity and stack size is 0 now, and app will close immidately if stack size is 0.
so you have to remove super.onbackpress() Method.