Passing information back from UITableViewDataSource to ViewController - ios

Question

I have a ViewController with a UITableView. As I wanted to split out the data handling I created an own class that answers UITableViewDataSource.
This class is supposed to first fetch data from CoreData and afterwards from a REST API.
How can the DataSource talk back to the ViewController to tell it to call reloadData on the TableView?
What's the best practice here?
I thought about:
KVO the DataSource's data and when the array change call reloadData
Handing over a block (with [self.table reloadData]) to the DataSource which gets executed every time the data changes in the DataSource
Make the table property public on the ViewController so the DataSource could call reloadData (which I don't really like as an idea)
Have a property on the DataSource which holds the ViewController with the Table to use it as a delegate (which sounds to me like a loop)
Are there any smart ways to do it? Or even common practice how to solve this?
Update:
I'm less interested in code how to do implement a certain design pattern. I'm more interested in the reasoning why to chose one pattern over the other.

Answer 1

Without more details, it sounds like you need a callback here. There are several methods that will work. If you have a 1 to 1 relationship (meaning your dataSource only needs to talk to the VC), then this is a good case for either:
1.) A delegate. Create your own delegate protocol for your dataSource and then have the VC adhere to that protocol (be the delegate).
2.) Do the same thing just using a block for a callback.
KVO will work just fine as well, but the above two are more in line with your scenario.
You could add a tableView property to your custom data source but that then blurs the lines of why you created that class in the first place.

Answer 2

For situations like this, I prefer delegates.
#class CupcakePan;
#protocol CupcakePanDelegate <NSObject>
- (void)cupcakesAreReadyForPan:(CupcakePan *)pan;
#end
#interface CupcakePan : NSObject <UITableViewDataSource>
#property (weak) id<CupcakePanDelegate> delegate;
#end
#implementation CupcakePan
- (void)bakingComplete {
[self.delegate cupcakesAreReadyForPan:self];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [cupcakes count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
return [make a CupcakeCell];
}
#end
#interface CupcakeViewController <CupcakePanDelegate>
#end
#implementation CupcakeViewController
- (void)cupcakesAreReadyForPan:(CupcakePan *)pan {
[_tableView reloadData];
}
#end

Answer 3

I frequently use NSNotificationCenter for these types of interactions.
In your datasource write the following code:
#define ABCNotificationName #"ABCNotificationName"
#define ABCNotificationData #"ABCNotificationData"
// ...
[[NSNotificationCenter defaultCenter] postNotificationName:ABCNotificationName object:self userInfo:#{ ABCNotificationData: data }];
In your view controller do the following:
-(void)loadView {
// setup your view
[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(datasourceUpdated:) name:ABCNotificationName object:dataSource];
}
-(void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
-(void)dataSourceUpdated:(NSNotification*)notification {
id data = notification.userInfo[ABCNotificationData];
// respond to the event
[self.tableView reloadData];
}
Note, that if you don't have any piece of data to communicate back to the controller it becomes even easier. In your datasource write the following code:
#define ABCNotificationName #"ABCNotificationName"
// ...
[[NSNotificationCenter defaultCenter] postNotificationName:ABCNotificationName object:self];
In your view controller do the following:
-(void)loadView {
// setup your view
[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(datasourceUpdated) name:ABCNotificationName object:dataSource];
}
-(void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
-(void)dataSourceUpdated {
// respond to the event
[self.tableView reloadData];
}