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问题:

I have custom UILabel which works fine on iOS6 and iOS7. But on iOS8 this label's (void)layoutSubviews method never get called. I create this label with initWithFrame, so this method should be called - and it's called on another iOS versions. What happens with autoLayout system in iOS8?

回答1:

I just want to add this answer because the question title may lead a lot of ppl here with similar issues (like me).

With iOS 8 to 8.0.2 LayoutSubviews calls are unreliable. They may not be called ever or (in my case) are called in a loop.

Even though you should not do it, it was pretty safe to alloc stuff in LayoutSubviews, but with this buggy (?!) behaviour it can cause hard-to-trace bugs.

I don't know if 8.1 fixes all the issues but it will be some time until customer devices will run 8.1 and they do run 8.0.2 NOW

回答2:

I had same issue. Really layoutSubviews is not called anymore for UILabel on iOS8, as Apple does not expect anybody uses it as superview.

I am using ReactiveCocoaLayout, so it can be done by subscribing to rcl_frameSignal or rcl_boundsSignal.

-(void)awakeFromNib { [ self.rcl_boundsSignal subscribeNext: ^( NSValue* boundsValue ) { //layout changed } ]; }

Or you can use simple KVO to know when frame has been changed:

-(void)dealloc
{
   [ self removeObserver: self forKeyPath: @"layer.bounds" ];
}

-(void)observeValueForKeyPath:( NSString* )keyPath
                     ofObject:( id )object
                       change:( NSDictionary* )change
                      context:( void* )context
{
   if ( [ keyPath isEqualToString: @"layer.bounds" ] )
   {
      //layoutSubviews
   }
   else
   {
      [ super observeValueForKeyPath: keyPath
                      ofObject: object
                        change: change
                       context: context ];
   }
}

-(void)awakeFromNib
{
   [ self addObserver: self
           forKeyPath: @"layer.bounds"
              options: NSKeyValueObservingOptionNew
              context: 0 ];
}