UISegmentedControl With AutoLayout Misaligns Title

问题

I have a custom UITableViewCell that has a label on the left side a UISegmentedControl on the right. I'm just getting used to using Auto Layout in code, and this is what I have in my custom cell (using UIView+AutoLayout):

-(void)updateConstraints
{
    self.titleLabel.translatesAutoresizingMaskIntoConstraints = NO;
    self.segmentedControl.translatesAutoresizingMaskIntoConstraints = NO;

    [self.titleLabel pinToSuperviewEdges:JRTViewPinLeftEdge inset:DB_AUTOLAYOUT_DEFAULT_INSET];
    [self.titleLabel centerInContainerOnAxis:NSLayoutAttributeCenterY];
    [self.segmentedControl pinToSuperviewEdges:JRTViewPinRightEdge inset:DB_AUTOLAYOUT_DEFAULT_INSET];
    [self.segmentedControl pinAttribute:NSLayoutAttributeBaseline
                            toAttribute:NSLayoutAttributeBaseline
                                 ofItem:self.titleLabel];

    [super updateConstraints];
}

My problem is that the segmented control's first title is always misaligned:

This is what it looks like on iOS 6:

And on iOS 7:

So first question is: How do I fix this?

Other, tangential question: Am I doing the right thing by putting auto layout code in updateConstraints or should I just apply the constraints once?

回答1:

In short from UIView.h

If you do all of your constraint set up in -updateConstraints, you might never even receive updateConstraints if no one makes a constraint. To fix this chicken and egg problem, override this method to return YES.

+ (BOOL)requiresConstraintBasedLayout {
        return YES; 
}

来源：https://stackoverflow.com/questions/23295530/uisegmentedcontrol-with-autolayout-misaligns-title