What does FragmentManager and FragmentTransaction exactly do?

Question

I have simple code below

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, mFeedFragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();

What do these lines of code do?

Answer 1

getFragmentManager()

Return the FragmentManager for interacting with fragments associated with this activity.

FragmentManager which is used to create transactions for adding, removing or replacing fragments.

fragmentManager.beginTransaction();

Start a series of edit operations on the Fragments associated with this FragmentManager.

The FragmentTransaction object which will be used.

fragmentTransaction.replace(R.id.fragment_container, mFeedFragment);

Replaces the current fragment with the mFeedFragment on the layout with the id: R.id.fragment_container

fragmentTransaction.addToBackStack(null);

Add this transaction to the back stack. This means that the transaction will be remembered after it is committed, and will reverse its operation when later popped off the stack.

Useful for the return button usage so the transaction can be rolled back. The parameter name:

Is an optional name for this back stack state, or null.

See for information the other question What is the meaning of addToBackStack with null parameter?

The Last statement commits the transaction and executes all commands.

See the google documentation for more help:

http://developer.android.com/reference/android/support/v4/app/FragmentActivity.html http://developer.android.com/reference/android/app/FragmentManager.html http://developer.android.com/reference/android/app/FragmentTransaction.html