CODEWITHSUNDEEP
iosuiscrollview
Daniel Brown
Daniel Brown

Reputation: 1164

How to sync scroll with multiple UIScrollViews?

I have 2 UIScrollViews displaying an image each (overview and zoom mode). I can scroll in both views already individually, now I want to keep the centerpoint of both views in sync.

I guess when one of the views is creating events, I need to forward them also to the other view, just can't find out which functions are relevant. Any hints?

edit: If parallel live scrolling is not possible, I want to at least sync after a scroll event.

Upvotes: 8

Views: 7842

Answers (2)

staticVoidMan
staticVoidMan

Reputation: 20274

This is not specific to the requirement here but helps in syncing scrollViews among different classes.

To sync scrollViews between different classes, use NSNotificationCenter to observe for a particular notification.

When scroll occurs then within the -scrollViewDidScroll: delegate method, use NSNotificationCenter to post the notification (with userInfo contents as scrollView.contentOffset.x & scrollView.contentOffset.y) Example: 

-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
NSMutableDictionary *userInfo = [[NSMutableDictionary alloc]init];
[userInfo setObject:[NSNumber numberWithFloat:scrollView.contentOffset.x]
          forKey:@"offsetX"];
[userInfo setObject:[NSNumber numberWithFloat:scrollView.contentOffset.y]
          forKey:@"offsetY"];

[[NSNotificationCenter defaultCenter] postNotificationName:@"scrollSync"
                                      object:nil
                                      userInfo:userInfo];
}

Register for this notification in the same class or anyother class and perform the -setContentOffset: method on the scrollView/s you want synced.
.
Example on Adding Observer (either in didLoad or init or anywhere suitable to you in as many classes as you like):

[[NSNotificationCenter defaultCenter] addObserver:self
                                      selector:@selector(handleNotification:)
                                      name:@"scrollSync" object:nil];

.
Example of the Selector Method

-(void)handleNotification:(NSNotification *)sender
{
float newX = [[sender.userInfo objectForKey:@"offsetX"] floatValue];
float newY = [[sender.userInfo objectForKey:@"offsetY"] floatValue];

[myOtherScrollView setContentOffset:CGPointMake(newX,newY)];
}

Upvotes: 3

Richard J. Ross III
Richard J. Ross III

Reputation: 55583

Check out the functions

You can link this together in the delegate method -scrollViewDidScroll:, which is constantly called while the user is scrolling.

Upvotes: 15

Related Questions