Found nil when trying to read from table cell in Swift - iphone

Question

I have a problem I do not understand since I am new to iPhone app programming and Swift.
I have a TableView in Swift which I use to display some results on. I have added a button to each cell such that the user can choose different cells and then press delete in order to delete the results shown in the cell.
For just a few number of results that worked just fine but now I have started to get nil-exception.
The program crashes in the function getIndexToDelete when I try to get the cell for a certain row.
Here is the code where I handle the table:
import UIKit
class DailyResultTable: UIViewController, UITableViewDataSource, UITableViewDelegate {
var results = Results()
var yearShownIndex = 0
var monthShownIndex = 0
var dayShownIndex = 0
#IBOutlet weak var tableView: UITableView!
#IBOutlet weak var DeleteButton: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
// self.view.backgroundColor = UIColor(patternImage: UIImage(named: "StatisticBackground")!)
}
// DataSource
func numberOfSectionsInTableView(tableview: UITableView) -> Int {
return 1
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// return (self.results?.getDayList(yearShownIndex, posMonth: monthShownIndex).count)!
print("return number of rows")
if (results.getYearList().count > 0 ){
if (results.getMonthList(yearShownIndex).count > 0){
if (results.getDayList(yearShownIndex, posMonth: monthShownIndex).count > dayShownIndex){
return (results.getDayList(yearShownIndex, posMonth: monthShownIndex)[dayShownIndex].results.count)
}
}
}
print("No numbers to show return 0")
return 0;
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("DayResultCell", forIndexPath: indexPath) as! ResultTableCell
let row = indexPath.row
//cell.ResultField.text = String((results?.getDayList(yearShownIndex, posMonth: monthShownIndex)[row].day)!) + "/" + String((results?.getMonthList(yearShownIndex)[monthShownIndex].month)!)
let res = results.getDayList(yearShownIndex, posMonth: monthShownIndex)[dayShownIndex].results[row].result
let maxRes = results.getDayList(yearShownIndex, posMonth: monthShownIndex)[dayShownIndex].results[row].maxresult
let discipline = results.getDayList(yearShownIndex, posMonth: monthShownIndex)[dayShownIndex].results[row].discipline
let text1 = String(res) + "/"
let text2 = String(maxRes)
let text3 = " - " + discipline
let text = text1 + text2 + text3
print(text)
cell.ResultField.text = text
return cell
}
// Delegate
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
}
#IBAction func CheckBox(sender: UIButton) {
let image = UIImage(named: "Selected") as UIImage!
let selected = sender.selected
sender.selected = !selected
sender.setImage(image, forState: .Selected)
}
func getIndexToDelete()->[Int]{
var indices = [Int]()
for i in 0..<tableView.numberOfRowsInSection(0){
let indexPath = NSIndexPath(forRow: i, inSection: 0)
// Here does the program crash
let cell = tableView.cellForRowAtIndexPath(indexPath) as! ResultTableCell
if (cell.CheckBoxButton.selected){
indices += [i]
}
}
return indices
}
#IBAction func DeletePressed(sender: UIButton) {
let deleteIndices = getIndexToDelete()
var goback = false;
var count = 0;
for index in deleteIndices{
print("Count: " + String(count))
results.ListResults[yearShownIndex].months[monthShownIndex].day[dayShownIndex].results.removeAtIndex(index-count)
count += 1
print(String((results.getDayList(yearShownIndex, posMonth: monthShownIndex)[dayShownIndex].results.count)));
}
loadView()
results.recreatePlainResult()
results.saveResults()
if (results.ListResults[yearShownIndex].months[monthShownIndex].day[dayShownIndex].results.count == 0){
print(String(results.ListResults[yearShownIndex].months[monthShownIndex].day.count))
results.ListResults[yearShownIndex].months[monthShownIndex].day.removeAtIndex(dayShownIndex)
results.recreatePlainResult()
results.saveResults()
print(String(results.ListResults[yearShownIndex].months[monthShownIndex].day.count))
goback = true
}
if (results.ListResults[yearShownIndex].months[monthShownIndex].day.count == 0){
results.ListResults[yearShownIndex].months.removeAtIndex(monthShownIndex)
results.recreatePlainResult()
results.saveResults()
goback = true
}
if (results.ListResults[yearShownIndex].months.count == 0){
results.ListResults.removeAtIndex(monthShownIndex)
results.recreatePlainResult()
results.saveResults()
goback = true
}
if (goback){
// return;
navigationController?.popViewControllerAnimated(true)
}
}
}
Here is the ResultTableCell:
import UIKit
class ResultTableCell: UITableViewCell {
#IBOutlet weak var ResultField: UITextField!
#IBOutlet weak var CheckBoxButton: UIButton!
}
I can of course put let cell = tableView.cellForRowAtIndexPath(indexPath) as! ResultTableCellinside an if-clause, but then other strange things happens.

Answer 1

Don't use !.
cellForRowAtIndexPath returns UITableViewCell? and can be nil if the row isn't visible when you make the call.
Check whether you actually got a cell at all using if let before casting it to your expected object type.

Answer 2

There are a few things going on here, let's take them one at a time:
The crash is from forcing the nil value through the ! that part should be obvious.
The for loop goes from 0 through to the number of rows, but UITableViewCell instances get recycled, so that can't work.
The checkbox selection is not the standard iOS table cell selection but something more custom
If you were using the built-in selection behavior of UITableViewyou could use this method.
If you want to continue using your custom checkbox selection, than probably the easiest way to do that is to listen for the selection change and build up the NSIndexPath as things are selected.
Afterward when the delete button is pressed you will have a pre-built index ready to delete and you won't have to loop to search for what is selected.