Delete UITableViewCell row with NSMutableArray throws exception

Question

I have a tableview and the data inside each cell is an NSMutableArray. I want to delete a row of the tableview each time I swipe left and press the delete button. However it is difficult with an NSMutableArray. I get a Sigabrt everytime I input the code toDoItems.removeObjectAtIndex(indexPath.row).

The error I get is

Terminating with uncaught exception of type NSException 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'

Any help on this problem?

Here is code relating to the problem.

ViewDidLoad code containing toDoItems:

let userDefaults:NSUserDefaults = NSUserDefaults.standardUserDefaults()

        let itemListFromUserDefaults:NSMutableArray? = userDefaults.objectForKey("itemList") as? NSMutableArray

        if ((itemListFromUserDefaults) != nil){
            toDoItems = itemListFromUserDefaults!
        }

My NSMutableArray variable

var toDoItems:NSMutableArray! = NSMutableArray()

My commitEditingStyle function:

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath){

    if(editingStyle == UITableViewCellEditingStyle.Delete){


        //This code gives me the error and Sigabrt
        toDoItems.removeObjectAtIndex(indexPath.row)



        tbl?.reloadData();


    }

My numberOfRowsInSection function:

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int{


        return toDoItems.count
    }

My cellForRowAtIndexPath function:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) ->
    UITableViewCell{

        let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as! TableView

            let toDoItem:NSDictionary = toDoItems.objectAtIndex(indexPath.row) as! NSDictionary
            cell.lbl.text = toDoItem.objectForKey("itemTitel") as? String

            return cell



}

Here is the error

MyPlanner[12373:461118] * Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object' * First throw call stack: ( 0 CoreFoundation 0x0000000109df3d85 exceptionPreprocess + 165 1 libobjc.A.dylib 0x0000000109867deb objc_exception_throw + 48 2 CoreFoundation 0x0000000109df3cbd +[NSException raise:format:] + 205 3 CoreFoundation 0x0000000109de9dae -[__NSCFArray removeObjectAtIndex:] + 94 4 MyPlanner 0x0000000109210c53 _TTSf4dg_n_g_n___TFC9MyPlanner14ViewController9tableViewfTCSo11UITableView18commitEditingStyleOSC27UITableViewCellEditingStyle17forRowAtIndexPathCSo11NSIndexPath_T_ + 131 5 MyPlanner 0x000000010920fc3d _TToFC9MyPlanner14ViewController9tableViewfTCSo11UITableView18commitEditingStyleOSC27UITableViewCellEditingStyle17forRowAtIndexPathCSo11NSIndexPath_T_ + 61 6 UIKit 0x000000010ac124c0 -[UITableView animateDeletionOfRowWithCell:] + 205 7 UIKit 0x000000010abe7a3e __52-[UITableView _swipeActionButtonsForRowAtIndexPath:]_block_invoke + 80 8 UIKit 0x000000010ac13eaa -[UITableView _actionButton:pushedInCell:] + 172 9 UIKit 0x000000010ae3aae6 -[UITableViewCell _actionButtonPushed:] + 82 10 UIKit 0x000000010aab4a8d -[UIApplication sendAction:to:from:forEvent:] + 92 11 UIKit 0x000000010ac27e67 -[UIControl sendAction:to:forEvent:] + 67 12 UIKit 0x000000010ac28143 -[UIControl _sendActionsForEvents:withEvent:] + 327 13 UIKit 0x000000010ac27263 -[UIControl touchesEnded:withEvent:] + 601 14 UIKit 0x000000010af9cc52 _UIGestureRecognizerUpdate + 10279 15 UIKit 0x000000010ab2748e -[UIWindow _sendGesturesForEvent:] + 1137 16 UIKit 0x000000010ab286c4 -[UIWindow sendEvent:] + 849 17 UIKit 0x000000010aad3dc6 -[UIApplication sendEvent:] + 263 18 UIKit 0x000000010aaad553 _UIApplicationHandleEventQueue + 6660 19 CoreFoundation 0x0000000109d19301 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION + 17 20 CoreFoundation 0x0000000109d0f22c __CFRunLoopDoSources0 + 556 21 CoreFoundation 0x0000000109d0e6e3 __CFRunLoopRun + 867 22 CoreFoundation 0x0000000109d0e0f8 CFRunLoopRunSpecific + 488 23 GraphicsServices 0x000000010ec78ad2 GSEventRunModal + 161 24 UIKit 0x000000010aab2f09 UIApplicationMain + 171 25 MyPlanner 0x00000001092134fd main + 125 26 libdyld.dylib 0x000000010d43d92d start + 1 ) libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)

Here is the code where I put in the information(add items) in toDoItems.

@IBAction func ClickedforSelection(sender: AnyObject) {

    if delegate != nil {
        let information : NSString = txt1.text!

        delegate!.userDidEntredInformation(information)

    }

    let userDefaults:NSUserDefaults = NSUserDefaults.standardUserDefaults()

    var itemList:NSMutableArray? = userDefaults.objectForKey("itemList") as? NSMutableArray

    let dataSet:NSMutableDictionary = NSMutableDictionary()
    dataSet.setObject(txt.text!, forKey: "itemTitel")


    if ((itemList) != nil){ // data already available
        let newMutableList:NSMutableArray = NSMutableArray();

        for dict:AnyObject in itemList!{
            newMutableList.addObject(dict as! NSDictionary)
        }

        userDefaults.removeObjectForKey("itemList")
        newMutableList.addObject(dataSet)
        userDefaults.setObject(newMutableList, forKey: "itemList")


    }else{ // This is the first todo item in the list
        userDefaults.removeObjectForKey("itemList")
        itemList = NSMutableArray()
        itemList!.addObject(dataSet)
        userDefaults.setObject(itemList, forKey: "itemList")
    }

    userDefaults.synchronize()

What is the text associated with the NSException? Why does your delete code not handle the case where the information is coming from the filteredAppleProducts array? — Paulw11
– Paulw11, Commented Jun 13, 2016 at 1:25
@Paulw11 I took out filteredAppleProducts however it still is not working — Aryan Sharma
– Aryan Sharma, Commented Jun 13, 2016 at 1:55
Are there any line of code that you assign toDoItems as an normal array (not mutable)? Please show the code you init the toDoItems. — Son Le
– Son Le, Commented Jun 13, 2016 at 1:59
@SonLe I don't have any other codes that contain toDoItems, and where I init toDoItems is the first line of code shown var toDoItems: NSMutableArray! = NSMutableArray() — Aryan Sharma
– Aryan Sharma, Commented Jun 13, 2016 at 2:05

Paulw11 · Accepted Answer · 2016-06-13 02:27:47Z

2

NSUserDefaults objectForKey will always return immutable objects. Simply down casting it won't make it mutable. You need to create a mutable array from the immutable array that is returned:

let userDefaults:NSUserDefaults = NSUserDefaults.standardUserDefaults()

if let itemListFromUserDefaults = userDefaults.objectForKey("itemList") as? NSArray
    toDoItems = itemListFromUserDefaults.mutableCopy()
}

edited Jun 13, 2016 at 2:27

answered Jun 13, 2016 at 2:24

Paulw11

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6 Comments

Aryan Sharma Over a year ago

Can you please tell me where I should put that line of code.

Paulw11 Over a year ago

Wherever you have the code above that is retrieving the array from NSUserDefaults; viewDidLoad

Paulw11 Over a year ago

Also, since you are initialising toDoItems with an empty NSMutableArray there is no need to make it an implicitly unwrapped optional; you don't need the :NSMutableArray!

Aryan Sharma Over a year ago

there is one more problem, when I kill the app and run it again, the cells that I had deleted are still showing, where I want them to just be deleted and not showing.

Paulw11 Over a year ago

You need to write the array back to user defaults after you change it

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