I used to use public static member variables in order for the starting Activity to be able to read the values from the previous Activity. I know that it is not a good practice and that it involves risks and limitations like having several instances of the current Activity and get the wrong value from the static variable.
Now I use Parcelable and pass the parameters in Bundle, but it is a burden sometimes. For example, in my current project I have a ExpandableListView and the groups/children stored in a Map<group name, List<child>>. This list is in a Fragment which is inside a TabHost in a FragmentActivity. Clicking on a child in the list will launch another FragmentActivity with the same structure (TabHost and a Fragment inside). From this Fragment you can edit the child. The problem comes when I need to notify the list that the child has changed. Following the best practices I decided to use a Broadcast to send the modified child to the first Activity, and let it update the list.
If, instead of a Parcelable, I'd use a public static variable I just would need to call notifyDataSetChange() in the list to refresh because the actual object instance in the Map was modified. With the Parcelable, even if the object is the same, when it is modified is a different variable in a different memory region. When the first Activity receives the Broadcast, it needs to loop through all the childs in all the groups to check if it's the same object and replace itself with the broadcasted Parcelable.
What am I doing wrong? Or is it supposed to be like this? With this kind of issues I am really tempted to go the public static way :-P
PS: Something like this. Long arrow is Broadcast, short arrow is Activity telling the Fragment to replace the child in the Map and refresh the list.
Fragment Activity <----
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TabHost | |
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Fragment <--| |
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Fragment Activity |
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TabHost |
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Fragment --------------
From your first activity, you can startActivityForResult. Your second activity can then return the updated dataset. Your first activity can then reassign the data map to whatever onActivityResult picks up and you can use notifyDataSetChanged.