delete from table view when using json - ios

Question

I've created an application that pulls data from my external database using json and populates a table view. It all works fine but I now want to be able to delete one of the data items in the table view by sliding a delete button across. This is my code for my secondview controller that gives me an error message. In the header file I also set an NSMutableArray called json.
#import "SecondViewController.h"
#interface SecondViewController ()
#end
#implementation SecondViewController
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
// Custom initialization
}
return self;
}
-(void) getData:(NSData *) data{
NSError *error;
json = [ NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
[self.tableView reloadData];
}
-(void) start{
NSURL *url = [NSURL URLWithString:kGETUrl];
NSData *data = [NSData dataWithContentsOfURL:url];
[self getData:data];
}
- (void)viewDidLoad
{
[super viewDidLoad];
NSTimer *myTimer = [NSTimer timerWithTimeInterval:5.0 target:self selector:#selector(start) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:myTimer forMode:NSDefaultRunLoopMode];
[self start];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return [json count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell ==nil){
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
}
NSDictionary *info = [json objectAtIndex:indexPath.row];
cell.textLabel.text = [info objectForKey:#"name"];
cell.detailTextLabel.text = [info objectForKey:#"message"];
return cell;
}
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete)
{
[json removeObjectAtIndex:indexPath.row];
// Delete the row from the data source
[tableView deleteRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
// [tableView reloadData];
}
}
-(void)setEditing:(BOOL)editing animated:(BOOL)animated
{
[super setEditing:editing animated:animated];
[self.tableView setEditing:editing animated:animated];
}
I'm aware that I'd need to code it to delete from the actual DB using php, etc. But for now I just want it to delete from the table view. This is the error message I get : 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'

Answer 1

This line:
json = [ NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
gives you an immutable array (NSArray) but your code uses json like it is an NSMutableArray.
You have two choices:
1) Change the line to:
json = [[NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error] mutableCopy];
or
2) Change the line to:
json = [ NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error];

Answer 2

your JSON object is immutable i.e. It can not be modified.
You could pass the object into a NSMutableDictionary constructor and then use that to build your tableview / delete rows etc
NSMutableDictionary *mutableJSON = [NSMutableDictionary dictionaryWithDictionary:JSON];