Resizing UITextView Without Losing Constraints

Resizing UITextView Without Losing Constraints

I'm trying to figure out how to resize UITextView (and everything
actually) without losing constraints. Basically, I'm trying to layout a
page where most components can have variable sizes (like description). I
tried doing it with a simple use case where I have a UITextView and a
UIButton underneath. I want to make sure that the position of the button
is relative to the bottom of the UITextView.
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
CGRect frame = self.textView.frame;
int height = self.textView.contentSize.height;
frame.size.height = height;
self.textView.frame = frame;
}
What I ended up with is UITextView overlapping with UIButton. After doing
a bit of research, it seems that if I replace the frame, all constraints
are gone also. I tried copying the constraints over, but of course the
pointer is still pointing at the old frame so that didn't help at all.
Is there a good way to solve a very dynamically laid out page? I'm trying
to at least use interface builder rather than code everything.
EDITED
I tried updating the constraint as suggest, but that didn't actually
resize the UITextView. Did I do it incorrectly? When I get the constant
again, it's updated, but the height isn't changed visually.
int height = self.textView.contentSize.height;
NSArray *constraints = [self.textView constraints];
for(int i = 0; i < [constraints count]; i++){
NSLayoutConstraint *constraint = [constraints objectAtIndex:i];
NSLayoutAttribute attribute = [constraint firstAttribute];
CGFloat ori = [constraint constant];
if(attribute == NSLayoutAttributeHeight){
[constraint setConstant: (CGFloat)height];
}
CGFloat newHeight = [constraint constant];
}