Programming iOS 6, 3rd Edition

Web View State Restoration

If you provided an HTML string to your web view, then restoring its state when the app is relaunched is up to you. You can use the built-in iOS 6 state saving and restoration to help you, but you’ll have to do all the work yourself. The web view has a scrollView which has a contentOffset, so it’s easy to save the scroll position (as an NSValue wrapping a CGPoint) in encodeRestorableStateWithCoder:, and restore it in decodeRestorableStateWithCoder:. What the TidBITS News app does is to restore the scroll position initially into an instance variable:

-(void)decodeRestorableStateWithCoder:(NSCoder *)coder {
    // scroll position is a CGPoint wrapped in an NSValue
    self.lastOffset = [coder decodeObjectForKey:@"lastOffset"];
    // ... other stuff ...
    [super decodeRestorableStateWithCoder:coder];
}

Then we reload the web view content (manually); when the web view has loaded, we set its scroll position:

- (void)webViewDidFinishLoad:(UIWebView *)webView {
    if (self.lastOffset)
        webView.scrollView.contentOffset = self.lastOffset.CGPointValue;
    self.lastOffset = nil;
    // ...
}

If, however, a web view participates in state restoration, and if the web view had a URL request (not an HTML string) when the user left the app, the web view will automatically return to life containing that request in its request property, and with its Back and Forward lists intact. Thus, you can use the state restoration mechanism to restore the state of the web view, but you have to perform a little ...