Misunderstood "id" parameter in several methods of FragmentTransactionBuilder

[van048]

It is containerViewId rather than the fragment itself's id. So there is no sense to call methods like checkIdNotExist(mFragmentManager, id).

See Details in https://developer.android.com/reference/android/app/FragmentTransaction.html#add(int, android.app.Fragment, java.lang.String).

[Piasy]

Actually, the id, or tag, is used for removing a fragment, we do this by finding a fragment with id or tag, what it means exactly is not important here.

If the id/tag doesn't exist, FragmentManager will return null, and if we do a transaction with null, NPE will be thrown, so we want make sure we could find a fragment with the id/tag, so we call checkIdExist/checkTagExist.

What if multiple fragment has the same container id/tag? Maybe that's not we really want to do, so I choose to enforce every id/tag could only be bound to one fragment(by calling checkIdNotExist/checkTagNotExist when add). If you really want to bind multiple fragments with the same id/tag, do a normal fragment transaction is ok. Anyway, add transaction won't throw exception. In case of doing normal fragment transaction, you still need safe commit, to avoid activity state loss.

[van048]

Thanks for you reply. Clear now.