Prevent the keyboard covering the view

gistfile1.m

/**
 * Register keyboard notifications.
 */
-(void) registerKeyboardNotifications {
    trace(@"register keyboard notifications");
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    [center addObserver:self 
               selector:@selector(keyboardDidShow:) 
                   name:UIKeyboardWillShowNotification object:nil];
    [center addObserver:self 
               selector:@selector(keyboardWillHide:) 
                   name:UIKeyboardWillHideNotification object:nil];
}


/**
 * Unregister keyboard notifications.
 */
-(void) unregisterKeyboardNotifications {
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    [center removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [center removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}


/**
 * Scrolls up the view to prevent the keyboard covering the view.
 *
 * This adds a bottom inset whose height is equal to that of the keyboard, 
 * and then scrolls the view so that the keyboard covers the inset, and not the view.
 */
- (void)keyboardDidShow:(NSNotification *)notification
{
    CGFloat insetHeight = 0;
    {
        // the keyboard is mounted on the window object
        AppDelegate *delegate = (AppDelegate*) [[UIApplication sharedApplication] delegate];
        UIWindow *window = delegate.window;
        
        // UIKeyboardFrameEndUserInfoKey is key for the keyboard frame in screen coordinates
        NSDictionary *userInfo = [notification userInfo];
        CGRect keyboardFrame = [[userInfo objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
        
        // convert scrollview frame to window coordinates to account for rotations
        CGRect ownFrame = [window convertRect:self.scrollView.frame fromView:self.scrollView.superview];
        
        // calculate the area covered by the keyboard
        CGRect coveredFrame = CGRectIntersection(ownFrame, keyboardFrame);
        
        // convert back in case screen is rotated
        coveredFrame = [window convertRect:coveredFrame toView:self.scrollView.superview];
        
        // Now coveredFrame gives us exactly the area of our view that is covered,
        // and thus the hight is also the bottom inset we need to apply.
        
        insetHeight = coveredFrame.size.height;
    }
    
	// set inset
	self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, insetHeight, 0);
	self.scrollView.scrollIndicatorInsets = self.scrollView.contentInset;
    
    // scroll to bottom minus the inset
    CGFloat offset = [self.scrollView contentSize].height - self.scrollView.contentInset.bottom;
    CGPoint bottomOffset = CGPointMake(0, offset);
    [self.scrollView setContentOffset:bottomOffset animated:YES];
    
}


/**
 * Removes the inset previously applied.
 */
- (void)keyboardWillHide:(NSNotification *)notification {

    // read the animation settings of the keyboard
    NSTimeInterval animationDuration;
    UIViewAnimationCurve animationCurve;
    NSDictionary* userInfo = [notification userInfo];
    [[userInfo objectForKey:UIKeyboardAnimationCurveUserInfoKey] getValue:&animationCurve];
    [[userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey] getValue:&animationDuration];

    // Remove the inset using the animation settings of the keyboard.
    // This has the effect of moving the view down in sync with the keyboard.
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:animationDuration];
    [UIView setAnimationCurve:animationCurve];
    self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);
    self.scrollView.scrollIndicatorInsets = self.scrollView.contentInset;
    [UIView commitAnimations];
}