removeAllObjects crashes app

Question

I want to clear my array, what i did is,

I have tableview view in my app, first i am fetching data from server and loading it in tableView.

-(void)viewDidLoad{

  //fetching data from server using background thread and storing it in array called (msg_array)
  [table reloadData];

}

when last row comes on screen i want to fetch new data from server and i want to display it,

-(void)LoadMoreData{ //this method gets fire when last cell is on screen 

    if ([msg_array count]>0) 
    {
        [msg_array removeAllObjects];  //crashes here
    }

}

This gives the error:

Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '-[__NSArrayI removeAllObjects]: unrecognized selector sent to instance

Why does it cause a crash:

The array is allocated like this:

msg_array = [dictShow copy];

dictshow contains the data and copying it to msg_array and dictshow is mutabledictionary

(Taken from comments)

Answer 1

'-[__NSArrayI removeAllObjects]: unrecognized selector sent to instance

This means that the array doens't have the method you're trying to call. That's because it is an immutable array (NSArray), not mutable (NSMutableArray).

Either make it mutable if you want to mutate it. Or, replace:

[msg_array removeAllObjects];

with:

msg_array = @[];

---

Based on your comment, the array should be mutable. That means that you have a mutable property / instance variable, but that you're creating an immutable instance to store into it. Find that location and update it (to create / return a mutableCopy at least).