Why weak IBOutlet NSLayoutConstraint turns to nil when I make it inactive?

ios objective-c uikit iboutlet ios-autolayout
Andrey Chernukha picture Andrey Chernukha · Jun 27, 2016 · Viewed 11.5k times · Source

I have an IBOutlet NSLayoutConstraint in my app. Very simple:

@property (nonatomic, weak) IBOutlet NSLayoutConstraint* leftConstraint;

At some point I want to deactivate this constraint:

self.leftConstraint.active = NO;

It happens in a method called from cellForRowAtIndexPath:. And the constraint becomes nil right after the line above. However if I declare this property as strong then it's ok, it doesn't turn to nil. Can anybody explain why it happens?

Answer

Avi picture Avi · Jun 27, 2016

When your outlet is weak, the only strong reference is from the view's constraints property. Deactivating the constraint removes it from that array, so there are no more strong references.

Related questions

How to find topmost view controller on iOS

I've run into a couple of cases now where it would be convenient to be able to find the "topmost" view controller (the one responsible for the current view), but haven't found a way to do it. Basically the challenge …

Read More
How to Rotate a UIImage 90 degrees?

I have a UIImage that is UIImageOrientationUp (portrait) that I would like to rotate counter-clockwise by 90 degrees (to landscape). I don't want to use a CGAffineTransform. I want the pixels of the UIImage to actually shift position. I am using …

Read More
How can I delay a method call for 1 second?

Is there an easy way delay a method call for 1 second? I have a UIImageView that reacts on a touch event. When the touch is detected, some animations happen in the app. After one second, I want to call another …

Read More