FragmentTransactions and the Fragment Back Stack
The code in
showDetails() that pulls in your new details fragment (shown again in Listing 8–8) looks rather simple, but there’s a lot going on here. It’s worth spending some time to explain what is happening and why. If your activity is in multipane mode, you want to show the details in a fragment next to the title list. You may already be showing details, which means you may have a details fragment visible to the user. Either way, the resource ID
R.id.details is for the
FrameLayout for your activity, as shown in Listing 8–3. If you have a details fragment sitting in the layout because you didn’t assign any other ID to it, it will have this ID. Therefore, to find out if there’s a details fragment ...