Question

I’d like to listen/detect a didSelectRowAtIndexPath: change in viewController1 and then based on this selection change something in viewController2.

Any idea how I might go about doing this?

Answer 1

Use a KVO.

First create a @property in ViewController1.h:

@property (strong, nonatomic) NSIndexPath *selectedIndexPath;

In ViewController1.m:

@synthesize selectedIndexPath;

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    if(indexPath!=self.selectedIndexPath) self.selectedIndexPath = indexPath; //this will fire the property changed notification

In ViewController2.m, assuming you have a reference to ViewController1 (i.e. vc1) already, set up the Observer in your viewDidLoad:

-(void)viewDidLoad
{
     [super viewDidLoad];
     [vc1 addObserver:self forKeyPath:@"selectedIndexPath" options:NSKeyValueObservingOptionNew context:NULL];
     //other stuff

and lastly add the following somewhere in ViewController2

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    //inspect 'change' dictionary, fill your boots

    ...
}

eta:

You must also remove the observer in ViewController2’s dealloc:

-(void)dealloc
{
    [vc1 removeObserver:self forKeyPath:@"selectedIndexPath"];
    ...
}