R – Delegating UIScrollView doesn’t work – help needed!

cocoa-touchdelegatesiphoneuiscrollview

I'm seriously losing my hair because of simple task which turned to hell. So I have UIScrollView subclass – MyScrollView and UIViewController subclass StoryViewController using that scroll view. I need to know when scroll is scrolled so what do I do? I try to delegate!

// StoryViewController.h
@interface StoryViewController : UIViewController <UIScrollViewDelegate>

// StoryViewController.m
// init
scrollView  = [[MyScrollView alloc] init];
scrollView.delegate = self;

// delegated function
- (void)scrollViewDidScroll:(UIScrollView *)s {
    NSLog(@"TEST");
}

Edit: Some NSLogs

Self: <StoryViewController: 0xfce090>
ScrollView Delegate: <StoryViewController: 0xfce090>
WebView Delegate: <StoryViewController: 0xfb1a30>

Edit:UIWebView subclass (MyWebView) which is subview of MyScrollView works fine and (void)webViewDidFinishLoad:(UIWebView*)webView (in the same storyviewcontroller.m) prints message.

No errors, builds fine, runs fine. After scrolling – nothing gets printed.

What am I doing wrong?

Best Answer

This may be a red herring, but you're calling alloc and init, rather than alloc and initWithFrame:. I assume you're adding the scrollView in your viewDidLoad method? Is this a XIB-based controller? Have you tried adding the scrollview in the XIB file, and setting things up there? Have you tried adding other delegate methods?

Related Solutions

Iphone – Detect scrolling in Subclass of UIScrollView

I ran into the same problem creating a subclass of the UIScrollView but solved it this way. As mentioned above, you can set yourself (subclass instance) as the delegate however this is what I did.

In the sub class I overrode the following methods

//Override this to detect when the user is scrolling, this is also triggered during view
//layout.  Here you can check your deceleration rate and determine when the scrolling has
//grinded to a halt.
-(void)setContentOffset:(CGPoint)contentOffset

//Override this to detect when the view has been resized (just a handy override)
-(void)setFrame:(CGRect)frame;

As far as the other UIScrollViewDelegate methods, the View Controller should be responsible for handling those in my opinion.

Ios – UIWebView scrollView not calling scrollViewDidScroll on touch

As UIWebView internally implements UIScrollViewDelegate Methods. Its is unlikely that the UIScrollViewDelegate will get reassigned to other objects except the current UIWebView object. So, I found a small work around. You can subclass UIWebView implement the UIScrollViewDelegate methods in that class and don't forget to forward the method to super or else unexpected behavior may occur.

This is how I solved the above problem:

/////in WebView.h file
//////WebView is subclass of UIWebView
#import <UIKit/UIKit.h>

@interface WebView : UIWebView
 @property(nonatomic,weak) NSObject <UIScrollViewDelegate> *mScrollDelegate;
@end

//// in WebView.m file
#import "WebView.h"
@synthesize mScrollDelegate;
@implementation WebView

- (id)init
{
    self = [super init];
    if (self) {
        self.scrollView.delegate = self;
    }
    return self;
}

/////scrollViewDidScroll Method, Also I am forwarding it to super class UIWebView
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    [super scrollViewDidScroll:scrollView];
    if([self.mScrollDelegate respondsToSelector:@selector(scrollViewDidScroll:)]){
         [self.mScrollDelegate scrollViewDidScroll:scrollView];
    }
    NSLog(@"scrollViewDidScroll");
}

@end

And make sure your self.webView must be of type WebView. in SDDefinitionViewController.m

self.webView.mScrollDelegate = self;

Now your scrollViewDidScroll method in SDDefinitionViewController.m will get called

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