The DialogFragment's combination with BackStack confuses me and maybe someone could help me out.
From what I found out, there are 2 common ways of displaying the DialogFragment. Either through show() method or by normal adding the fragment through transaction (from the checkup that's essentialy what show() does internaly).
The problem I have is with understanding of where addToBackstack() method comes into this whole process, especialy when you add transaction to backstack prior to calling on show() method, like in this sample:
// DialogFragment.show() will take care of adding the fragment
// in a transaction. We also want to remove any currently showing
// dialog, so make our own transaction and take care of that here.
FragmentTransaction ft = getFragmentManager().beginTransaction();
Fragment prev = getFragmentManager().findFragmentByTag("dialog");
if (prev != null) {
ft.remove(prev);
}
ft.addToBackStack(null);
// Create and show the dialog.
DialogFragment newFragment = MyDialogFragment.newInstance(mStackLevel);
newFragment.show(ft, "dialog");
In the sample above, before displaying the new DialogFragment, we check for other DialogFragment that could be displayed, we remove it and add this procedure to the backstack (I assume that this is for the purpose of displaying the previous DialogFragment, when the new DialogFragment is removed). Afterwards we display the new DialogFragment through show() method. But I fail to see any difference between this approach, and just calling show() method. I just checked on a Test project with displaying multiple DialogFragments one on top of eachother in a succesion, and the internal implementation of DialogFragment handles everything automaticaly, meaning that when I touch back button, the previous DialogFragment is displayed nevertheless.
So, why the addToBackstack is being used in context of DialogFragments?
Alright, after writing more code using the DialogFragment solution including more tests I came to the reason (most likely the key reason) of why to use the addToBackStack way, right after removing the previous dialog.
The reason for it (silly me that I missed that) is that it will make sure only one dialog is visible at one point in time. The show() method does exactly what it says, it "shows" a new dialog fragment, but does absolutely nothing with any previous visible dialog, so in essence all the dialogs using show() method will be stacked on top of the previous dialog. My error was that I didn't realize that until I made dialogs different in size. If all dialogs are of the same size, then the most top one will be hiding all the other dialogs.
So to summarize, show() method does not hide/remove any dialog that is already present on the screen. If we want to do that, we need to do the transaction manually, which of course must include the removing of the previous dialog as well as adding this transaction to the back stack so that when user presses the back button, the previous dialog will reemerge.