How to handle empty objects with Swift? - ios

Question

I have an app that keeps track of monthly expenses. I have an Expense entity with a month attribute that keeps track of current month expense is created on. I would then display the expenses for each month in a table view as shown here. The user can only switch left and right only if there are expenses within the next or the last month
#IBAction func backMonthButtonPressed(sender: AnyObject) {
print("Back Button Pressed")
currentMonth = NSCalendar.currentCalendar().dateByAddingUnit(.Month, value: -1, toDate: currentMonth, options: [])!
if checkMonth(currentMonth) {
updateFetch()
setMonth()
} else {
currentMonth = NSCalendar.currentCalendar().dateByAddingUnit(.Month, value: 1, toDate: currentMonth, options: [])!
}
tableView.reloadData()
}
#IBAction func nextMonthButtonPressed(sender: AnyObject) {
print("Next Button Pressed")
currentMonth = NSCalendar.currentCalendar().dateByAddingUnit(.Month, value: 1, toDate: currentMonth, options: [])!
if checkMonth(currentMonth) {
updateFetch()
setMonth()
} else {
currentMonth = NSCalendar.currentCalendar().dateByAddingUnit(.Month, value: -1, toDate: currentMonth, options: [])!
}
tableView.reloadData()
}
func checkMonth(month : NSDate) -> Bool {
let app = UIApplication.sharedApplication().delegate as! AppDelegate
let context = app.managedObjectContext //scratch pad
let fetchRequest = NSFetchRequest(entityName: "Expense")
fetchRequest.predicate = NSPredicate(format: "month == %#", month.MonthYearDateFormatter())
let count = context.countForFetchRequest(fetchRequest, error: nil)
if count > 0 {
print("There are expenses for this month \(month.MonthYearDateFormatter()). Show expenses")
return true
} else {
print("There are no expenses for this month \(month.MonthYearDateFormatter()). Do Nothing")
return false
}
}
My problem is this, in the unlikely scenario that the user created an expense back in June and didn't create an expense in August. How can I let the user still see his/her expense back in August without skipping it. Any ideas?

Answer 1

I made some optimisation before elaboration:
#IBAction func backMonthButtonPressed(sender: AnyObject) {
self.processMonth(step: -1)
}
#IBAction func nextMonthButtonPressed(sender: AnyObject) {
self.processMonth(step: 1)
}
// a method uses almost the same code for both cases, so it was merged
func processMonth(step: Int) {
let direction = (step < 1 ? "Back" : "Next")
print("\(direction) Button Pressed")
currentMonth = NSCalendar.currentCalendar().dateByAddingUnit(.Month, value: step, toDate: currentMonth, options: [])!
//if checkMonth(currentMonth) {
// I wouldn't test this because it locks you out from seeing empty month.
updateFetch()
setMonth()
//}
tableView.reloadData()
}
An answer to what you've exactly asked:
If your data source for your UITableView is set properly, you should be able to go through empty months though
// changed return type from `Bool` to `void` as I suggested in the method not to test empty month, as it could be useless
func checkMonth(month : NSDate) {
let app = UIApplication.sharedApplication().delegate as! AppDelegate
let context = app.managedObjectContext //scratch pad
let fetchRequest = NSFetchRequest(entityName: "Expense")
fetchRequest.predicate = NSPredicate(format: "month == %#", month.MonthYearDateFormatter())
let count = context.countForFetchRequest(fetchRequest, error: nil)
if count > 0 {
print("There are expenses for this month \(month.MonthYearDateFormatter()). Show expenses")
} else {
print("There are no expenses for this month \(month.MonthYearDateFormatter()). Do Nothing")
// here you can make some additional actions, like seeting the empty table with "no expenses this month"
}
}
Anyway, as #Paulw11 noted, if your data source is not size-exhausting, you could rather fetch the data from your data-model at viewDidLoad/viewDidAppear for example and then to render each month according to the currentMonth variable (regarding what month a user currently see).
So as a result, you would call setMonth() method only in the load of your controller and each time a user changes a current month view.

Answer 2

With the help of #Paulw11 and #pedrouan, I was able to do what I wanted.
Fetch all expenses
func fetchExpenses() {
let app = UIApplication.sharedApplication().delegate as! AppDelegate
let context = app.managedObjectContext //scratch pad
let fetchRequest = NSFetchRequest(entityName: "Expense")
//Always Sort Budget by the date it's created
let sortDescriptor = NSSortDescriptor(key: "created", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
do {
let results = try context.executeFetchRequest(fetchRequest)
self.expenses = results as! [Expense]
} catch let err as NSError {
print(err.debugDescription)
}
}
Set constraints to first and last month to determine how far a user can navigate through months in viewDidLoad
//If array is not empty, set first and last month
if expenses.count > 0 {
guard let first = expenses.first?.month else {
return
}
firstMonth = first
guard let last = expenses.last?.month else {
return
}
lastMonth = last
}else {
//Set current month to be first and last
firstMonth = currentMonth.MonthYearDateFormatter()
lastMonth = currentMonth.MonthYearDateFormatter()
}
Limit user from going past first and last month
#IBAction func backMonthButtonPressed(sender: AnyObject) {
print("Back Button Pressed")
if currentMonth.MonthYearDateFormatter() != firstMonth {
self.processMonth(step: -1)
}
}
#IBAction func nextMonthButtonPressed(sender: AnyObject) {
print("Next Button Pressed")
if currentMonth.MonthYearDateFormatter() != lastMonth {
self.processMonth(step: 1)
}
}
Return all the expenses in current month and if there's none clear fetch and return empty table.
func updateFetch() {
setFetchResults()
do {
try self.fetchedResultsController.performFetch()
} catch {
let error = error as NSError
print("\(error), \(error.userInfo)")
}
}
func setFetchResults() {
let app = UIApplication.sharedApplication().delegate as! AppDelegate
let context = app.managedObjectContext //scratch pad
//Fetch Request
let fetchRequest = NSFetchRequest(entityName: "Expense")
let sortDescriptor = NSSortDescriptor(key: "created", ascending: false)
fetchRequest.predicate = NSPredicate(format: "month == %#", currentMonth.MonthYearDateFormatter())
fetchRequest.sortDescriptors = [sortDescriptor]
let count = context.countForFetchRequest(fetchRequest, error: nil)
let controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: ad.managedObjectContext , sectionNameKeyPath: section, cacheName: nil)
//If there is none, empty fetch request
if count == 0 {
print("There are no expenses for this month. Show nothing")
controller.fetchRequest.predicate = NSPredicate(value: false)
} else {
print("There are expenses for this month. Show expenses")
}
fetchedResultsController = controller
controller.delegate = self
}
With pedroruan's processMonth(), I was able to navigate through empty tableViews so that user can see that August is empty while still being able to go to June's month. Thanks guys.