FYI: I've gotten this to work by modifying the tableHeaderView and re-setting it. In this case, i'm adjusting the size of the tableHeaderView when the UIWebView subview has finished loading.

[webView sizeToFit];

CGRect newFrame = headerView.frame;

newFrame.size.height = newFrame.size.height + webView.frame.size.height;

headerView.frame = newFrame;

[self.tableView setTableHeaderView:headerView];

This answer is old and apparently doesn't work on iOS 7 and above.

I ran into the same problem, and I also wanted the changes to animate, so I made a subclass of UIView for my header view and added these methods:

- (void)adjustTableHeaderHeight:(NSUInteger)newHeight{

    NSUInteger oldHeight = self.frame.size.height;

    NSInteger originChange = oldHeight - newHeight;



    [UIView beginAnimations:nil context:nil];



    [UIView setAnimationDuration:1.0f];

    [UIView setAnimationDelegate:self];

    [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)];



    self.frame = CGRectMake(self.frame.origin.x, 

                        self.frame.origin.y, 

                        self.frame.size.width, 

                        newHeight);



    for (UIView *view in [(UITableView *)self.superview subviews]) {

        if ([view isKindOfClass:[self class]]) {

            continue;

        }

        view.frame = CGRectMake(view.frame.origin.x, 

                            view.frame.origin.y - originChange, 

                            view.frame.size.width, 

                            view.frame.size.height);

    }



    [UIView commitAnimations];

}



- (void)animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context{

    [(UITableView *)self.superview setTableHeaderView:self];

}

This essentially animates all the subviews of the UITableView that aren't the same class type as the calling class. At the end of the animation, it calls setTableHeaderView on the superview (the UITableView) – without this the UITableView contents will jump back the next time the user scrolls. The only limitation I've found on this so far is if the user attempts to scroll the UITableView while the animation is taking place, the scrolling will animate as if the header view hasn't been resized (not a big deal if the animation is quick).

If you want to conditionally animate the changes you can do the following:

- (void) showHeader:(BOOL)show animated:(BOOL)animated{



    CGRect closedFrame = CGRectMake(0, 0, self.view.frame.size.width, 0);

    CGRect newFrame = show?self.initialFrame:closedFrame;



    if(animated){

        // The UIView animation block handles the animation of our header view

        [UIView beginAnimations:nil context:nil];

        [UIView setAnimationDuration:0.3];

        [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];



        // beginUpdates and endUpdates trigger the animation of our cells

        [self.tableView beginUpdates];

    }



    self.headerView.frame = newFrame;

    [self.tableView setTableHeaderView:self.headerView];



    if(animated){

        [self.tableView endUpdates];

        [UIView commitAnimations];

    }

}

Please note that the animation is two-folded:

1. The animation of the cells below the tableHeaderView. This is done using beginUpdates and endUpdates
   


2. The animation of the actual header view. This is done using a UIView animation block.

In order to synchronize those two animations the animationCurve has to be set to UIViewAnimationCurveEaseInOut and the duration to 0.3, which seems to be what the UITableView uses for it's animation.

Update

I created an Xcode project on gihub, which does this.
Check out the project ResizeTableHeaderViewAnimated in besi/ios-quickies

I think it should work if you just set the height of myHeaderView like so:

CGRect newFrame = myHeaderView.frame;

newFrame.size.height = newFrame.size.height + 100;

myHeaderView.frame = newFrame;



self.tableView.tableHeaderView = myHeaderView;

Used @garrettmoon solution above until iOS 7.

Here's an updated solution based on @garrettmoon's:

- (void)adjustTableHeaderHeight:(NSUInteger)newHeight animated:(BOOL)animated {



    [UIView beginAnimations:nil context:nil];



    [UIView setAnimationDuration:[CATransaction animationDuration]];

    [UIView setAnimationDelegate:self];

    [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)];



    self.frame = CGRectMake(self.frame.origin.x,

                        self.frame.origin.y,

                        self.frame.size.width,

                        newHeight);



    [(UITableView *)self.superview setTableHeaderView:self];



    [UIView commitAnimations];

}



- (void)animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context{

    [(UITableView *)self.superview setTableHeaderView:self];

}

This worked for me on iOS 7 and 8. This code is running on the table view controller.

[UIView animateWithDuration:0.3 animations:^{

    CGRect oldFrame = self.headerView.frame;

    self.headerView.frame = CGRectMake(oldFrame.origin.x, oldFrame.origin.y, oldFrame.size.width, newHeight);

    [self.tableView setTableHeaderView:self.headerView];

}];

Its because the setter of tableHeaderView.

You have to set the UIView height before set the tableHeaderView. (Would be much easier if Apple open sources this framework...)

On iOS 9 and below, tableHeaderView would not re-layout after resizing it.
This issue is resolved in iOS 10.

To solve this issue, just do it with the following code:

self.tableView.tableHeaderView = self.tableView.tableHeaderView;

On iOS 9.x, doing this on viewDidLoad works just fine:

var frame = headerView.frame

frame.size.height = 11  // New size

headerView.frame = frame

headerView is declared as @IBOutlet var headerView: UIView! and connected on the storyboard, where it is placed at the top of the tableView, to function as the tableHeaderView.

Setting the height for header view property tableView.tableHeaderView in viewDidLoad seems not work, the header view height still not change as expected.

After fighting against this issue for many tries. I found that, you can change the height by invoking the header view create logic inside the
- (void)didMoveToParentViewController:(UIViewController *)parent method.

So the example code would look like this:

- (void)didMoveToParentViewController:(UIViewController *)parent {

    [super didMoveToParentViewController:parent];



    if ( _tableView.tableHeaderView == nil ) {

        UIView *header = [[[UINib nibWithNibName:@"your header view" bundle:nil] instantiateWithOwner:self options:nil] firstObject];



        header.frame = CGRectMake(0, 0, CGRectGetWidth([UIScreen mainScreen].bounds), HeaderViewHeight);



        [_tableView setTableHeaderView:header];

    }

}

I found the initWithFrame initializer of a UIView doesn't properly honor the rect I pass in. Hence, I did the following which worked perfectly:

 - (id)initWithFrame:(CGRect)aRect {



    CGRect frame = [[UIScreen mainScreen] applicationFrame];



    if ((self = [super initWithFrame:CGRectZero])) {



        // Ugly initialization behavior - initWithFrame will not properly honor the frame we pass

        self.frame = CGRectMake(0, 0, frame.size.width, 200);



        // ...

    }

}

The advantage of this is it is better encapsulated into your view code.

I have implemented animated height change of the table's header to expand to overall screen when tapped. However, the code can help in other cases:

// Swift

@IBAction func tapped(sender: UITapGestureRecognizer) {



    self.tableView.beginUpdates()       // Required to update cells. 



    // Collapse table header to original height

    if isHeaderExpandedToFullScreen {   



        UIView.animateWithDuration(0.5, animations: { () -> Void in

            self.scrollView.frame.size.height = 110   // original height in my case is 110

        })



    }

    // Expand table header to overall screen            

    else {      

        let screenSize = self.view.frame           // "screen" size



        UIView.animateWithDuration(0.5, animations: { () -> Void in

            self.scrollView.frame.size.height = screenSize.height

        })

    }



    self.tableView.endUpdates()  // Required to update cells. 



    isHeaderExpandedToFullScreen= !isHeaderExpandedToFullScreen  // Toggle

}

UITableView resizing header - UISearchBar with Scope Bar

I wanted a UITableView with a UISearchBar as the header to the table so I have a hierarchy that looks like this

UITableView

  |

  |--> UIView

  |     |--> UISearchBar

  |

  |--> UITableViewCells

UISearchBarDelegate methods

As has been stated elsewhere, if you don't setTableViewHeader after changing it, nothing will happen.

- (BOOL)searchBarShouldBeginEditing:(UISearchBar *)searchBar

{

    searchBar.showsScopeBar = YES;

    [UIView animateWithDuration:0.2f animations:^{

        [searchBar sizeToFit];

        CGFloat height = CGRectGetHeight(searchBar.frame);



        CGRect frame = self.tableView.tableHeaderView.frame;

        frame.size.height = height;

        self.tableHeaderView.frame = frame;

        self.tableView.tableHeaderView = self.tableHeaderView;

    }];



    [searchBar setShowsCancelButton:YES animated:YES];

    return YES;

}



- (BOOL)searchBarShouldEndEditing:(UISearchBar *)searchBar

{

    searchBar.showsScopeBar = NO;

    [UIView animateWithDuration:0.f animations:^{

        [searchBar sizeToFit];



        CGFloat height = CGRectGetHeight(searchBar.frame);



        CGRect frame = self.tableView.tableHeaderView.frame;

        frame.size.height = height;

        self.tableHeaderView.frame = frame;

        self.tableView.tableHeaderView = self.tableHeaderView;

    }];



    [searchBar setShowsCancelButton:NO animated:YES];

    return YES;

}

If custom headerView is designed using autolayout and headerView needs to be updated after web-fetch or similar lazy task.
then in iOS-Swift I did this and got my headerView updated using bellow code:

//to reload your cell data

self.tableView.reloadData()

dispatch_async(dispatch_get_main_queue(),{

// this is needed to update a specific tableview's headerview layout on main queue otherwise it's won't update perfectly cause reloaddata() is called

  self.tableView.beginUpdates()

  self.tableView.endUpdates()

} 

Obviously, by now Apple should have implemented UITableViewAutomaticDimension for tableHeaderView & tableFooterView...

The following seems to work for me using layout contraint(s):

CGSize   s  = [ self  systemLayoutSizeFittingSize : UILayoutFittingCompressedSize ];

CGRect   f  = [ self  frame ];



f.size   = s;



[ self  setFrame : f ];

If your tableHeaderView is a content adjustable webView,you can try:

[self.webView.scrollView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:nil];



- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {

    self.webView.height = self.webView.scrollView.contentSize.height;

    self.tableView.tableHeaderView = self.webView;

}

I tested it on iOS9 and iOS11,worked well.

This is only for when you use auto-layout and set translatesAutoresizingMaskIntoConstraints = false to a custom header view.

The best and the simplest way is to override intrinsicContentSize. Internally UITableView uses intrinsicContentSize to decide its header/footer size. Once you have override intrinsicContentSize in your custom view, What you need to do is as below

1. configure the custom header/footer view's layout(subviews)


2. invoke invalidateIntrinsicContentSize()
   


3. invoke tableView.setNeedsLayout() and tableView.layoutIfNeeded()
   

Then the UITableView's header/footer will be updated as you want. No need to set the view nil or reset.

One thing really interesting for the UITableView.tableHeaderView or .tableFooterView is that UIStackView loose its ability to manage its arrangedSubviews. If you want to use UIStackView as a tableHeaderView or tableFooterView, you have to embed the stackView in a UIView and override UIView's intrinsicContentSize.