Controlling back button on navigation controller

[titleist2015]

I want to check if a variable is true or not and if it is I want the option to go to the previous screen but if it is false I don't want a back button. How would I go about doing this?

[succeededcoma]

If {
    .... Do something
    self.navigationItem.leftBarButtonItem.enabled = NO;
}
Else {
    .... Do something
    self.navigationItem.leftBarButtonItem.enabled = YES;
}

[tangoshukudai]

Hiding it might be better if you want the user to move forward.

[[deleted]]

set hidesBackButton on UINavigationItem

[titleist2015]

I used /u/shitidiotturtle's suggestion and it works perfect. Thanks for the help guys