Passing Delegate through multiple hierarchy - iphone

Question

I wrote a custom class, TagsScrollView, which displays tags inside a scroll view.
When the tags are pressed, TagsScrollView relies on its delegate to implement what to do. Almost all the time, this involves:
Changing the tab index to another index
Pushing TagsDetailVC to the current navigation controller.
Right now, this is how my app is structured:
Dotted line indicates a "has" relationship. MainVC has a FeedView, which has a few FeedCellViews, which in turn has a TagsScrollView each.
Solid line indicates a "push" relationship. ImageDetailVc is pushed onto the navController of MainVC.
How can I organize my code such that TagsScrollView's delegate can be pointed at MainVC elegantly?
right now I have defined the following:
TagsScrollView.h
#protocol TagPressedDelegate<NSObject>
#required
- (void)tagPressed:(id)sender forQuery:(NSString *)query;
#end
FeedCellView.m
self.tagsScrollView.tagPressedDelegate = self.tagPressedDelegate
FeedView.m
self.cells[0].tagPressedDelegate = self.tagPressedDelegate
MainViewVC.m
self.feed.tagPressedDelegate = self
....
- (void)tagPressed...
How can I avoid this pattern? What can I do better? Should I have TagsScrollViewDelegate extend ScrollViewDelegate instead?

Answer 1

You can definitely do better, remove the delegation pattern, use blocks.
Add a block based property to your TagsScrollView .h file
#property (copy, nonatomic) void (^tagPressedBlock)(id sender, NSString *query);
in the .m file add the related callbacks
- (void)tagPressed:(id)sender {
if (_tagPressedBlock) {
_tagPressedBlock(sender, self.query); // I'm assuming that the query is your iVar
}
}
assign the property like this
tagsScrollView.tagPressedBlock = ^(id sender, NSString *query) {
// do stuff with those parameters
}
That's for "doing it better"
As for how to pass a tag pressed event to your MainVC class, you should use NSNotificationCenter.
Define the notification name somewhere globally visible, for instance I'd suggest creating a Defines.h file and #including it in your Prefix.pch file.
Anyway, define the notification name:
static NSString *const TagPressedNotification = #"TagPressedNotification";
Next publish that notification when the -tagPressed: is executed and encapsulate the valuable information into the userInfo dictionary:
- (void)tagPressed:(id)sender {
[[NSNotificationCenter defaultCenter] postNotificationName:TagPressedNotification object:nil userInfo:#{#"sender" : sender, #"query" : self.query, #"scrollView" : self.tagScrollView}];
//.. code
}
Next add your MainVC as an observer to that notification:
MainVC.m
- (void)viewDidLoad {
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(tagPressed:)
name:TagPressedNotification
object:nil];
}
And implement -tagPressed: method in your MainVC
- (void)tagPressed:(NSNotification *)notification {
id sender = notification.userInfo[#"sender"];
NSString *query = notification.userInfo[#"query"];
TagScrollView *scrollView = notification.userInfo[#"scrollView"];
if (scrollView == myScrollView) { // the one on your mainVC
// do stuff
}
}
Add don't forget to clean yourself out of NotificationCenter's register:
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
easy
edit
I suppose you should also pass the scroll view, which is the sender, since your mainVC contains that scroll view as well. Edited the code
Another edit
Create an enumeration define in your Defines.h file
enum {
TagSenderTypeFeed = 1,
TagSenderTypeImageDetail
};
typedef NSInteger TagSenderType;
When creating a notification add appropriate enum value to your notification's userInfo dictionary #"senderType" : #(TagSenderTypeFeed)