WebView - User has scrolled - scroll

Question

I cannot figure out how to have a WebView in Objective-c detect when a scroll has been made. I have looked at the WebFrameLoadDelegate: and found didChangeLocationWithinPageForFrame: method, but that did seem to work.

Answer 1

You'll want to detect the webview is scrolling by using javascript. If you do a quick google search on "uiwebview javascript" you'll see plenty of examples on how to have javascript run in the uiwebivew. Once you get the javascript to detect the scroll occurring then you have the javascript change window.location to something fake and implement the "webView:shouldStartLoadWithRequest:navigationType:" delegate to execute objective-c code. Return NO from the delegate method to not load the request.

Answer 2

Depends on whether you are using a UIWebView (iOS - Cocoa Touch) or WebView (OS X - Cocoa).
iOS (iOS 5 and later):
UIWebView exposes its UIScrollView, and you can set the scroll view's delegate and then implement the delegate scrollViewDidScroll: delegate method (adding to your class's #interface declaration first, of course; this example is in a UIViewController subclass):
- (void)viewDidLoad {
[super viewDidLoad];
[_webView.scrollView setDelegate:self];
}
#pragma mark UIScrollViewDelegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
// do something in response to scroll
}
}
OS X:
Add an observer for the NSViewBoundsDidChangeNotification of the WebView (this example is in an NSWindowController subclass):
- (id)initWithWindowNibName:(NSString *)windowNibName {
self = [super initWithWindowNibName:windowNibName];
if (self) {
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(_scrollDetected)
name:NSViewBoundsDidChangeNotification
object:_webView];
}
return self;
}
- (void)_scrollDetected {
// do something in response to scroll
}

Answer 3

On OS X, you can detect it by subscribing to NSScrollViewWillStartLiveScrollNotification:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(mySelector:)
name:NSScrollViewWillStartLiveScrollNotification object:nil];
I pass nil as the object parameter because when I get it, it doesn't appear to actually come from the enclosingScrollView on the WebView. And there is no scroll view property on WKWebView in Yosemite. So when handling it, you have to check if it's your web view sending it (being paranoid about type safety):
-(void)handleScroll:(id)sender
{
if ([sender isKindOfClass:[NSNotification class]])
{
NSNotification *notif = (NSNotification *)sender;
if ([notif.object isKindOfClass:[NSView class]])
{
NSView *view = (NSView *)notif.object;
if ([view isDescendantOf:self.webView])
{
//Handle scroll here
}
}
}
}
I have only tried this descendent-checking thing with WebView, so if you're using WKWebView, YMMV.
There are other scroll notifications listed in the NSScrollView documentation.