Pass data from custom UITableViewCell and UIViewController - ios

Question

I am (fairly) familiar with segues and delegates to pass data between UIViewControllers, but my current situation is slightly different and I cannot get it working. Context: XCode 5 and iOS7 with Objective C.
I have a tableview (dynamic prototypes) that loads a custom cell (from a separate nib) that contains a UILabel and a UISwitch. CustomCell.xib loads its data from CustomCell.h/m. The main content is in ViewController.h/m and in that file I need to know whether the switch value changed (or actually the new value of the UISwitch). Obviously I know this within the CustomCell.h/m files but need to pass them to ViewController.h/m.
I tried using a delegate, but I cannot set a delegate for the UINib instance (in contrast to setting a delegate on a viewcontroller's instance). Also, the custom cell is implemented in the viewcontroller, so it is not pushed like another viewcontroller would be in a navigation stack.
CustomCell.h
#import <UIKit/UIKit.h>
#protocol CustomCellDelegate <NSObject>
- (void)switchControlValueChanged:(UISwitch*)switchControl toNewValue:(BOOL)value;
#end
#interface CustomCell : UITableViewCell
#property (nonatomic, weak) IBOutlet UILabel *titleLabel;
#property (nonatomic, weak) IBOutlet UISwitch *switchControl;
#property (nonatomic, assign) id <CustomCellDelegate> delegate;
- (void)setValueForSwitchControlTo:(BOOL)value;
- (IBAction)changeColorForSwitchControl;
#end
CustomCell.m
- (void)changeColorForSwitchControl // value changed method
{
...
[self.delegate switchControlValueChanged:self.switchControl toNewValue:self.switchControl.on];
}
ViewController.h
#import <UIKit/UIKit.h>
#import "CustomCell.h"
#interface ViewController : UITableViewController <CustomCellDelegate>
...
#end
ViewController.m
- (void)viewDidLoad
{
...
// cannot set a delegate on the cellNib
UINib *cellNib = [UINib nibWithNibName:kCustomCell bundle:nil];
[self.tableView registerNib:cellNib forCellReuseIdentifier:kCustomCell];
}
- (void)switchControlValueChanged:(UISwitch *)switchControl toNewValue:(BOOL)value
{
NSLog(#"Switch changed!"); // this is not getting displayed
}

Answer 1

The right time to set your view controller to be the delegate of your cell would be when you set up other attributes of your cell. You do that in tableView:cellForRowAtIndexPath:.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:kCustomCell forIndexPath:indexPath];
...
cell.delegate = self;
return cell;
}
Side note: registerNib:forCellReuseIdentifier: does exactly what it says, it just registers your nib for reuse. The contents of the nib aren't loaded until the table view decides to do that. It creates copies of the cell contained in the nib as and when required.

Answer 2

One option would be to use NSNotification, not as elegant but would work for your purpose. Every time the switch value changes, you can send a notification in CustomCell.m, something like:
NSDictionary *cellInfo = #{}; // add useful information to identify the cell to this dictionary
[[NSNotificationCenter defaultCenter] postNotificationName:#"SwitchValueChanged" object:nil userInfo:cellInfo];
Then you catch the notification in your ViewController by registering it as an observer with:
-(void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(yourMethod) name:#"SwitchValueChanged" object:nil];
}