Question

Is it a good pattern to add a @protocol to a Model class and implement it in the Controller?

Here is the a code which I use to send message to reload UITableView when My Model data changes, is it a good approach for object c codding?:

MyModel.h

@protocol myModelDelegate
{
(void) refreshTableView:(id) sender;
}
@end

@interface MyModel
{
@property (nonatomic,strong) (NSArray *) myData;
@property (nonatomic,weak) (id) <myModelDelegate> delegate;
}
@end

MyModel.m

@implementation MyModel

@synthesize myData=_myData;

    - (NSArray*) myData {
    if(!_myData) {
    _myData= [[NSArray alloc] init];
    }

    return _myData;
    }

 - (void) setMyData: (NSArray*) myData
    {
         if (_myData != myData) {
        _myData=myData;
    [delegate refreshTableView:self];
                           }
    }

@end

myDataController.h

...
@interface MyDataController: UITableViewController <myModelDelegate>
...

myDataController.m

@interface MyDataController()
        @property (nonatomic,strong) (MyModel *) model;
@end

@implementation MyDataController

@synthesize model=_model;

-(MyModel *) model
{
if(!_model)
  {
    _model=[[MyModel alloc]init];
     model.delegate=self;
  }
return _model;
}
    ...
        - (void) refreshTableView: (id) sender
        {
          [TableView reloadData];
        }
    ...
@end

Answer 1

I don’t see any problem with this design.

The only thing I would change is the signature of the delegate method into:

-(void)modelDidChange:(MyModel*)model;

This is more in line with best-practices you see around about naming of delegate methods, and also hints to a broader semantics of the method: the model will “signal’ the fact that it changed; the delegate will take an action upon that (i.e., refreshing a table if it’s a table; storing the model content, if it’s a perstistence component, etc.)