When there are more than two MVC controllers, controllers need to pass data or send notifications between two controllers. For example, a table list controller, parent, may push to an item edit controller, child, when an item is selected. The easiest way to is to set a property in child controller and pass the reference to parent controller to child's property. However, this strategy has one drawback: strong binding between parent and child controllers. In case the parent controller is changed to another kind of controller, the property of child has to be updated.
The alternative way is to implement delegate in Objective-C. Define a delegate in .h, then keep communication by defined methods in the delegate. Here is the steps of this strategy.
Define a Delegate
The delegate provides APIs to pass data or to send notifications. For example, the following codes define a update method:
@protocol MyEntityEditDelegate <NSObject>
- (void) updateEntity:(NSIndexPath *)index;
@end
Add a Delegate Property in Parent Controller
The next step is to implement the delegate property in the parent controller. This breaks the strong binding between the parent and child. The child will call parent by the delegate APIs.
@interface ParentListViewController :
UITableViewController <..., MyEntityEditDelegate>
....
@end
Define a Delegate Property in Child Controller
The last step is to add delegate property in the child controller. This will let the child hold a reference to its parent by delegate.
@interface ChildEntityEditViewController : ...
@property (nonatomic, weak) id<MyEntityEditDelegate> delegate;
@end
Notice that the property type is id<...> type. This prevents the coupling between the parent and child.
I t has been two weeks after my vacation from China. I read a news from Melaleuca about weight lost program. Basically, the program works in a simple way: reduce daily large meals into small ones, meal size like my fist. Take GC Attain or Attain between meals to replace snack food. Exercise 45 minutes daily, and take a Access bar before walk out. Optional: take PfoFlex20 within one hour after exercise.
Posts
