Auto Layout with UITextField causes exception - ios

Question

I'd like to position a UITextField inside a UIViewController view using auto layout (dynamic resizing and a 5 pt margin between the textfield and its superview). I create the view programmatically using the loadView method.
Header of UIViewController
#property (weak, nonatomic) UITextField *textField;
Implementation
-(void)loadView{
//Frame
UIView *frame = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 40)];
[self setView:frame];
[self.view setBackgroundColor:[UIColor redColor]];
//TextField
[self.textField setDelegate:self];
[self.textField setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.textField setBackgroundColor:[UIColor blueColor]];
[frame addSubview:self.textField];
[frame addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-(5#50)-[textField(==10#10)]-(5#50)-|"
options:0
metrics:nil
views:#{#"textField" : self.textField}]];
[frame addConstraints:[NSLayoutConstraint constraintsWithVisualFormat: #"V:|-(5#50)-[textField(==10#10)]-(5#50)-|"
options:0
metrics:nil
views:#{#"textField" : self.textField}]];
// //Test with UIView instead
// UIView *sub = [[UIView alloc]init];
// [sub setTranslatesAutoresizingMaskIntoConstraints:NO];
// [sub setBackgroundColor:[UIColor greenColor]];
// [frame addSubview:sub];
//
// [frame addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-(5#50)-[sub(==10#10)]-(5#50)-|"
// options:0
// metrics:nil
// views:#{#"sub" : sub}]];
//
// [frame addConstraints:[NSLayoutConstraint constraintsWithVisualFormat: #"V:|-(5#50)-[sub(==10#10)]-(5#50)-|"
// options:0
// metrics:nil
// views:#{#"sub" : sub}]];
Running this throws an exception. Curiously using a UIView ("sub") as subview instead (the part commented out) does work as expected.
Ouput:
Shouldn't the textfield behave just like this UIView? How come the textField causes an exception?
New finding: The app crashes only when I use addConstraints on the self.textField. If I remove those two calls I spare the crash, however the textfield doesn't show up either.

Answer 1

NSLayoutConstraint is only part of IOS 6. if you try to work this code other than IOS6
( such as IOS 5, IOS 4.3) you are highly likely get this runtime error.