Question

I am currently developing an iPad application. For business reasons there wont be any data persistence on the device. The data will be accessed from a back-end server as needed using NSURLConnection. I have developed a ‘model’ object which does all the network access. The UI has a split view controller with a table view controller inside a UINavigationControlller as the root controller. User will drill-down on the table view controller to eventually load the detail view controller. The table Viewcontrollers are passing a reference to the model object when they are being loaded into the UINavigationController so that they can dynamically generate parts of the Table View Cell from the model. In order to be responsive, each Table View controller sets itself as the delegate of the Model object in the view will appear and when the cell is selected, queries the model object, which in turn updates the UI via a delegate method.

My question is where is the best place to set and unset the delegate of the data model?. Currently I am setting the delegate in the ViewWillAppear and setting it to nil immediately after navigation Controller:pushViewController:Animated.

// Setting the delegate
- (void)viewWillAppear:(BOOL)animated {
// set ourself as the delegate
[[self dataModel] setDelegate:self];

// Get the count of studies
[[self dataModel]GetListOfDiagnosticStudyResultsForID:[[self currentPatient]patientID]];

}

// setting delegate to nil
DiagnosticStudiesViewController *selectedVC = [[DiagnosticStudiesViewController alloc] init];
selectedVC.dataModel = self.dataModel;
[[self dataModel]setDelegate:nil];
[[self navigationController]pushViewController:selectedVC animated:YES];

Is this appropriate? Could you think of any issues with this pattern. The program is very responsive and I do not see any issues in the instruments. Is there a better way to do this?.

Sorry that this question is long winded.

Answer 1

I think this is an okay approach but there are a couple of considerations to be made:

• You’re sharing the dataModel with 2 views so you may have to update the view when you return to the DiagnosticsStudiesViewController’s parent (self in your code) depending on how dataModel data is displayed.
• This might get hairy in the future if you need to thread your code. In that case you might have to make a copy of the dataModel to pass to DiagnosticsStudiesViewController or handle edits to dataModel in a thread-safe manner.
• You’ll obviously require a network connection for both view controllers to work so you’ve made a workflow decision with your two view controllers by pulling dataModel from the server. In the future it may be hard to uncouple these view controllers.

If it works for your case and the decision has been made to not persist I think you’ll be fine.