When is layoutSubviews called

Question

I have a custom view that s not getting layoutSubview messages during animation   I have a view that fills the screen  It has a custom subview at the bottom of the screen that correctly resizes in Interface Builder if I change the height of the nav bar  layoutSubviews is called when the view is created  but never again  My subviews are correctly laid out  If I toggle the in-call status bar off  the subview s layoutSubviews is not called at all  even though the main view does animate its resize   Under what circumstances is layoutSubviews actually called   I have autoresizesSubviews set to NO for my custom view  And in Interface Builder I have the top and bottom struts and the vertical arrow set     Another part of the puzzle is that the window must be made key    window makeKeyAndVisible     of else the subviews are not automatically resized

User · Answer

Building on the previous answer by  BadPirate  I experimented a bit further and came up with some clarifications corrections  I found that layoutSubviews  will be called on a view if and only if    Its own bounds  not frame  changed  The bounds of one of its direct subviews changed  A subview is added to the view or removed from the view    Some relevant details    The bounds are considered changed only if the new value is different  including a different origin  Note specifically that is why layoutSubviews  is called whenever a UIScrollView scrolls  as it performs the scrolling by changing its bounds  origin  Changing the frame will only change the bounds if the size has changed  as this is the only thing propagated to the bounds property  A change in bounds of a view that is not yet in a view hierarchy will result in a call to layoutSubviews  when the view is eventually added to a view hierarchy  And just for completeness  these triggers do not directly call layoutSubviews  but rather call setNeedsLayout  which sets raises a flag  Each iteration of the run loop  for all views in the view hierarchy  this flag is checked  For each view where the flag is found raised   layoutSubviews  is called on it and the flag is reset  Views higher up the hierarchy will be checked called first

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When migrating an OpenGL app from SDK 3 to 4  layoutSubviews was not called anymore  After a lot of trial and error I finally opened MainWindow xib  selected the Window object  in the inspector chose Window Attributes tab  leftmost  and checked  Visible at launch   It seems that in SDK 3 it still used to cause a layoutSubViews call  but not in 4   6 hours of frustration put to an end

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https   developer apple com library prerelease tvos documentation WindowsViews Conceptual ViewPG iPhoneOS CreatingViews CreatingViews html   apple ref doc uid TP40009503-CH5-SW1     Layout changes can occur whenever any of the following events happens   in a view       a  The size of a view   s bounds rectangle changes    b  An interface orientation change occurs  which usually triggers a change in the root view   s bounds rectangle    c  The set of Core Animation sublayers associated with the view   s layer changes and requires layout    d  Your application forces layout to occur by calling the  setNeedsLayout  or  layoutIfNeeded  method of a view    e  Your application forces layout by calling the  setNeedsLayout  method of the view   s underlying layer object

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I had a similar question  but wasn t satisfied with the answer  or any I could find on the net   so I tried it in practice and here is what I got    init does not cause layoutSubviews to be called  duh   addSubview  causes layoutSubviews to be called on the view being added  the view it   s being added to  target view   and all the subviews of the target view setFrame intelligently calls layoutSubviews on the view having its frame set only if the size parameter of the frame is different scrolling a UIScrollView causes layoutSubviews to be called on the scrollView  and its superview rotating a device only calls layoutSubview on the parent view  the responding viewControllers primary view  Resizing a view will call layoutSubviews on its superview   My results - http   blog logichigh com 2011 03 16 when-does-layoutsubviews-get-called

User · Answer

Some of the points in BadPirate s answer are only partially true    For addSubView point      addSubview causes layoutSubviews to be called on the view being added  the view it   s being added to  target view   and all the subviews of the target    It depends on the view s  target view  autoresize mask  If it has autoresize mask ON  layoutSubview will be called on each addSubview  If it has no autoresize mask then layoutSubview will be called only when the view s  target View  frame size changes   Example  if you created UIView programmatically  it has no autoresize mask by default   LayoutSubview will be called only when UIView frame changes not on every addSubview   It is through this technique that the performance of the application also increases  For the device rotation point     Rotating a device only calls layoutSubview on the parent view  the responding viewController s primary view    This can be true only when your VC is in the VC hierarchy  root at window rootViewController   well this is most common case  In iOS 5  if you create a VC  but it is not added into any another VC  then this VC would not get any noticed when device rotate  Therefore its view would not get noticed by calling layoutSubviews

User · Answer

calling   self view setNeedsLayout    in viewController makes it to call viewDidLayoutSubviews

User · Answer

I tracked the solution down to Interface Builder s insistence that springs cannot be changed on a view that has the simulated screen elements turned on  status bar  etc    Since the springs were off for the main view  that view could not change size and hence was scrolled down in its entirety when the in-call bar appeared   Turning the simulated features off  then resizing the view and setting the springs correctly caused the animation to occur and my method to be called   An extra problem in debugging this is that the simulator quits the app when the in-call status is toggled via the menu  Quit app   no debugger

User · Answer

have you looked at layoutIfNeeded   The documentation snippet is below  Does the animation work if you call this method explicitly during the animation   layoutIfNeeded Lays out the subviews if needed   -  void layoutIfNeeded   Discussion Use this method to force the layout of subviews before drawing   Availability Available in iPhone OS 2 0 and later

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A rather obscure  yet potentially important case when layoutSubviews never gets called is   import UIKit  class View  UIView        override class var layerClass  AnyClass   return Layer self        class Layer  CALayer           override func layoutSublayers                    if we don t call super layoutSublayers                  print type of  self    function                       override func layoutSubviews                    this method never gets called by the OS          print type of  self    function           let view   View frame  CGRect x  0  y  0  width  100  height  100

[ios] When is layoutSubviews called?

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