Implementing back stacks with fragments

问题:

I'm attempting to implement a back stack while using fragments, but when using the Back button, I keep getting taken out of the app to the home screen.

Activity opens fragment A; Fragment A has a clickable TextView that opens fragment B (this works). Hitting BACK should return me to fragment A, but it takes me to the home screen instead.

Here is the activity's call to the opening of fragment A in onCreate:

    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.add(R.id.fragment_layout_container, new FragmentLogin(), "fragment_login")
            .addToBackStack("login_screen")
            .commit();

    Log.d("Back", getFragmentManager().getBackStackEntryCount() +" <- Entry Count at LoginActivity.onCreate" );

At this point, the Log prints 0 <- Entry Count at LoginActivity.onCreate. Something I've done wrong keeps this from printing 1.

Then, the Fragment A has this listener:

    forgottenPassword.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_layout_container, new FragmentForgottenPassword(), "fragment_password")
                    .addToBackStack("forgotten_password")
                    .commit();

            Log.d("Back", getFragmentManager().getBackStackEntryCount() + " <- Entry Count at FragmentLogin.onCreateView.Listener");
        }
    });

The Log here prints 1 <- Entry Count at FragmentLogin.onCreateView.Listener. Here, the listener works and opens fragment B - but the back button returns me to the home screen.

回答1:

Use this in your Activity it should pop out the fragments already added to backstack

 @Override
 public void onBackPressed()
 {
     if (getFragmentManager().getBackStackEntryCount() > 0) {
         getFragmentManager().popBackStack();
     } else {
         super.onBackPressed();
     }
 }

回答2:

Try Like This,

 public void replaceFragment(Fragment fragment, boolean addToBackStack) {

    FragmentTransaction transaction = getFragmentManager()
            .beginTransaction();

    if (addToBackStack) {
        transaction.addToBackStack(null);

    } else {
        getFragmentManager().popBackStack(null,
                FragmentManager.POP_BACK_STACK_INCLUSIVE);

    }
    transaction.replace(R.id.fragment_layout_container, fragment);
    transaction.commitAllowingStateLoss();
    getFragmentManager().executePendingTransactions();

}

and Used it like this,

replaceFragment(new FragmentForgottenPassword(), true);

回答3:

There is a GitHub library that will do this work for you!
https://github.com/rathodchintan/Fragment-Back-Stack
Whenever you are displaying any new fragment, just push that fragment into stack using following code. //here this fragment is our first fragment
homeListFragment = new HomeListFragment(); fragmentStack.push(homeListFragment);
It has many other stack options too.