How to replace fragment C with fragment A when back button is pressed?

You need to do 2 things - name the FragmentTransaction from A->B and then override onBackPressed() in your containing activity to call FragmentManager#popBackStack (String name, int flags) when you are on Fragment C. Example:

Transition from A->B

getSupportFragmentManager()  .beginTransaction()  .replace(R.id.container, new FragmentB(), "FragmentB")  .addToBackStack("A_B_TAG")  .commit();

Transition from B->C will use a similar transaction with "FragmentC" as its tag.

Then in your containing Activity override onBackPressed():

@Overridepublic void onBackPressed() {  if (getSupportFragmentManager().findFragmentByTag("FragmentC") != null) {    // I'm viewing Fragment C    getSupportFragmentManager().popBackStack("A_B_TAG",      FragmentManager.POP_BACK_STACK_INCLUSIVE);  } else {    super.onBackPressed();  }}

Theory

Use the addToBackStack(tag: String): FragmentTransaction method from within the FragmentTransaction in order to mark a point where you want to return to. This method returns the FragmentTransaction instance for chain-ability only.

Then Return with the popBackStackImmediate(tag: String, flag: int): void method from the FragmentManager. The tag is what you specified before. The flag is either the constant POP_BACK_STACK_INCLUSIVE to include the transaction marked or 0.

Example

What follows is an example with the following layout having a FrameLayout with id content_frame where the fragments are loaded into.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" ><TextView    android:id="@+id/textView"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="@string/hello_world" /><FrameLayout    android:id="@+id/content_frame"    android:layout_below="@id/textView"    android:layout_width="match_parent"    android:layout_height="match_parent" /></RelativeLayout>

The code below marks a fragment by it's fragment class name when replacing the content of the layout element with id content_frame.

public void loadFragment(final Fragment fragment) {        // create a transaction for transition here    final FragmentTransaction transaction = getSupportFragmentManager()            .beginTransaction();                // put the fragment in place    transaction.replace(R.id.content_frame, fragment);    // this is the part that will cause a fragment to be added to backstack,    // this way we can return to it at any time using this tag    transaction.addToBackStack(fragment.getClass().getName());    transaction.commit();}

And to complete this example a method that allows you to get back to that exact same fragment using the tag when you loaded it.

public void backToFragment(final Fragment fragment) {    // go back to something that was added to the backstack    getSupportFragmentManager().popBackStackImmediate(            fragment.getClass().getName(), 0);    // use 0 or the below constant as flag parameter    // FragmentManager.POP_BACK_STACK_INCLUSIVE);}

When implementing this for real you might want to add a null check on the fragment parameter ;-).

This is how I do it..

With FragmentA.java and any other fragments.

Replace your fragment with its class name as tag:

private void showFragment(Fragment fragment){        if(fragment != null){            getSupportFragmentManager().beginTransaction().replace(R.id.container,fragment,fragment.getClass().getSimpleName()).commit();        }    }

Now in onBackPressed():

@Override    public void onBackPressed()    {if(getSupportFragmentManager().findFragmentByTag("FragmentA") == null)            showFragment(new FragmentA());        else            super.onBackPressed();    }