Animating objects from off screen loss of response

Question

I have a UIViewController. Within that is a UITableView which is drawn at origin 0,0. I also have a UIScrollView that is drawn at 0,-80 so that it is off screen and not visible.

When a menu button is pressed, I animate the UIViewController's frame down 80px to reveal the UIScrollView.

The problem here is that the UIScrollView does not respond at all.

If I draw the UIScrollView at say 0,0, where it IS visible on load, it works fine. I can even animate it off screen then back on screen with no issue.

---

Here is how my view looks before animating:

 _____________________________
|                             |  Frame -> (0,-80, 320, 80)                  
|      ScrollView             |  **Offscreen**
|_____________________________|
|                             |  <- Original view (0,0,320,480)
|                             |
|                             |
|                             |
|                             |
|                             |
|       Original View         |
|                             |
|                             | 
|                             |
|                             |
|                             |
|                             |
|                             |
|                             |
|                             |
|                             |
|_____________________________|

---

When I animate I do the following:

[UIView animateWithDuration:0.3 
                      delay:0.0 
                    options:(UIViewAnimationOptionAllowUserInteraction |
                             UIViewAnimationOptionCurveEaseIn) 
                 animations:^{ 
                         self.view.frame = CGRectMake(0.0, (self.view.frame.origin.y + container.frame.size.height), self.view.frame.size.width, self.view.frame.size.height);
                        scroll.userInteractionEnabled = YES;
                     } 

                 completion:^(BOOL finished) { 
                         if (scrollLoaded == NO) {
                             [self loadFavorites]; 
                             scrollLoaded = YES;
                         }
                     }];

---

Now my view looks like this after animating:

 _____________________________
|                             |  Frame -> (0, -80, 320, 80)              
|      ScrollView             |  
|_____________________________|
|                             |  <- Original view (0, 80, 320, 480)
|                             |
|                             |
|                             |
|                             |
|                             |
|       Original View         |
|                             |
|                             | 
|                             |
|                             |
|                             |
|                             |
|                             |
|_____________________________|
|                             |
|        **Offscreen**        |
|_____________________________|

---

I have subclassed my scrollView to listen more closely for events:

.h

#import <UIKit/UIKit.h>

@interface UIScrollView_ExtraTouch : UIScrollView

@end

.m

#import "UIScrollView+ExtraTouch.h"

@implementation UIScrollView_ExtraTouch

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"scrollview touchesBegan");
    [self.nextResponder touchesBegan:touches withEvent:event];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"scrollview touchesMoved");
    if(!self.dragging){
        [self.nextResponder touchesMoved:touches withEvent:event];
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"scrollview touchesEnded");
    [self.nextResponder touchesEnded:touches withEvent:event];
}

@end

---

Nothing goes to the log after the animation. Which I think means that since the frame is at -80, it believes it to be off screen, thus not receive any type of action.

Is this correct? If so is there a way to fix it?

Answer 1

The scroll view is outside of the original view so you cannot react with it. To fix create a wrapper view that is large enough to contain the whole content area(with scrollView & tableView both as subViews), add it to the original view, and animate this wrapper view instead of original view.

So wrapper view will be 320x560, and at 0,-80 in original view. Then move it up and down 80 as needed.