When does a UITableView's contentSize get set?

You can make the UITableView calculate the size of the content immediately by calling layoutIfNeeded on the UITableView. This will run all the necessary calculations to layout the UITableView.

Example for a UITableViewController subclass that you want to put in a container view with variable size:

Objective-C

- (CGSize)preferredContentSize
{
    // Force the table view to calculate its height
    [self.tableView layoutIfNeeded];
    return self.tableView.contentSize;
}

Swift

override var preferredContentSize: CGSize {
    get {
        // Force the table view to calculate its height
        self.tableView.layoutIfNeeded()
        return self.tableView.contentSize
    }
    set {}
}

While I don't love KVO (Key-Value Observing), it's a fairly good way to know exactly when your table's contentSize has changed (rather than just calling your update methods in a bunch of random places). It's rather simple to use (though somewhat cryptic and implicit). To observe changes on your table's contentSize, do the following:

1) Become an observer of your table's contentSize property like so:

[self.tableView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:NULL];

This is usually done in the view controller that holds the tableView (like in viewDidLoad:, for example).

2) Implement the KVO observing method and make the changes you need:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
    if(object == self.tableView && [keyPath isEqualToString:@"contentSize"]) {
        // perform your updates here
    }
}

3) Remove your view controller as an observer at some logical point (I call it in dealloc). You do this like so:

- (void)dealloc {
    [self.tableView removeObserver:self forKeyPath:@"contentSize"];
}

Try this:

- (void)resizeTableViewFrameHeight
{
    UITableView *tableView = self.tableView;
    CGRect frame = tableView.frame;
    frame.size.height = [tableView sizeThatFits:CGSizeMake(frame.size.width, HUGE_VALF)].height;
    tableView.frame = frame;
}