Saving Data on Android

Reading and wri/ng the prefs from 
MainAc/vity
Right now, in 
MainActivity.kt
, you're using hardcoded values for the sort order and 
the priority filters, which you pass on to the 
NoteAdapter
, to display notes in a 
different order and filter which notes should be in the list. The right way to do this, 
which involves 
SharedPreferences
, is to read a user's preferred ways of sorting and 
filtering, from prefs, and then passing those values to the 
NoteAdapter
.
To do this, change the way you create the 
priorities
 
Set
 by changing the 
statement to the following:
private
 
val
 priorities 
by
 lazy 
{ notePrefs.getNotePriorityFilters().toMutableSet() }
Instead of creating an empty mutable set and then adding values to it, you're now 
reading from the preferences, in a lazy way. Once you create the 
NoteAdapter
, the 
value will be assigned and you can use the 
priorities
.
Another change you have to make is the creation of the 
NoteAdapter
:
private
 
val
 noteAdapter: NoteAdapter 
by
 lazy { 
  NoteAdapter(
this
, 
      priorities, 
      notePrefs.getNoteSortOrder(), 
// Read from preferences
 
      ::showEditNoteDialog 
  ) 
}
Instead of passing in a hardcoded value for 
FILENAME_ASC
 as the 
NoteSortOrder
, 
you're reading from the preferences to get the ordering the user previously selected.
Note
: Do not attempt to modify a string set read from the prefs. The results 
can be unpredictable. Always make a copy of the set instead, if it is going to be 
modified, like in the case of this app. You can do that by calling 
toMutableSet()
, because Kotlin internally creates a new object, instead of 
just copying the 
Set
 value.
Saving Data on Android
Chapter 2: Shared Preferences
raywenderlich.com
46

---

The app can now load the saved preferences when the app launches, but it also needs 
to store the values anytime the menu options change. To do that, find 
updateNoteSortOrder()
 and insert the following, replacing the 
TODO
:
notePrefs.saveNoteSortOrder(sortOrder)
The line of code above will save the 
sortOrder
 to the prefs. Finally, find 
updateNotePrioritiesFilter()
 at the bottom of the 
MainActivity
 and insert this 
line of code, once again replacing the 
TODO
:
notePrefs.saveNotePriorityFilters(priorities)
The above statement will save the list of priority filters to the prefs. If you look in 
onOptionsItemSelected()
, the above two functions you just wrote the code for are 
called anytime the appropriate menu options are changed.
Finally, run the app. You can now filter and sort notes to your heart's content and the 
app will save your personalized preferences. Once you come back, everything will be 
ready and waiting for you!