What similar functionality method (viewWillAppear) exists on UIView? What similar functionality method (viewWillAppear) exists on UIView? ios ios

What similar functionality method (viewWillAppear) exists on UIView?


How about the following from the UIView reference

willMoveToSuperview:, didMoveToSuperview - Implement these methods as needed to track the movement of the current view in your view hierarchy.

this will at least tell you when it is added to a view hierarchy but there is no guarantee that the view hierarchy is presented/viewable.


No, but you can forward that notification to the desired view from your view controller.


  • Note, I was originally going to post this answer here but seeing as this was asked years prior I marked that one as a duplicate and will now answer here instead.

Macro Solution

I've made a macro solution for this that is very elegant and easy to use.


.m

Add the following to your .m

-(void)viewDidLoad {    //normal stuff}__METHOD_MACRO_wasRemovedFromSuperview() {    //Code here will run whenever this view is removed from its superview}__METHOD_MACRO_wasAddedAsSubview() {    //Code here will run whenever this view is added as the subview of another view}

Yup! It really is that easy!

(Due to how the ifdef toggling of the macro is set-up below, you can use one or the other or both!)


.h

Add the following to your .h beneath @end (or, if you want to keep things clean, you can simply add to a file called macros.h and #import it)

Note: If you add this (or import this) to multiple files that also import each other or @class each other you can end up messing up the #ifdef logic and this macro could fail, I suggest importing it from a separate .h file for each class you need it in, this macro was created more as a proof of concept than something to be used in production code

//Logic for __METHOD_MACRO_wasAddedAsSubview() and __METHOD_MACRO_wasRemovedFromSuperview()#define startSuppressingWarnings() \_Pragma("clang clang diagnostic push")\_Pragma("clang diagnostic ignored \"-Weverything\"")#define stopSuppressingWarnings() \_Pragma("clang clang diagnostic pop")#define __INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup() \-(void)didMoveToWindow {\[super didMoveToWindow];\if (self.window && self.superview) {\startSuppressingWarnings()/*Hide potential undeclared selector warnings*/\if ([self respondsToSelector:@selector(__wasAddedAsSubview)]) {\[self performSelector:@selector(__wasAddedAsSubview)];\}\stopSuppressingWarnings()\} else {\startSuppressingWarnings()/*Hide potential undeclared selector warnings*/\if ([self respondsToSelector:@selector(__wasRemovedFromSuperview)]) {\[self performSelector:@selector(__wasRemovedFromSuperview)];\}\stopSuppressingWarnings()\}\}#ifdef __INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup_wasSetup///Called when UIView was added as subview OR moved to another superview OR if another VC was presented#define __METHOD_MACRO_wasAddedAsSubview() \-(void)__wasAddedAsSubview/*{ //perform extra processes here }*/#else#define __INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup_wasSetup 1///Called when UIView was added as subview OR moved to another superview#define __METHOD_MACRO_wasAddedAsSubview() \__INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup() \-(void)__wasAddedAsSubview/*{ //perform extra processes here }*/#endif#ifdef __INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup_wasSetup///Called when UIView is removed as subview from superview or when its parent window is removed#define __METHOD_MACRO_wasRemovedFromSuperview() \-(void)__wasRemovedFromSuperview/*{ //perform extra processes here }*/#else#define __INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup_wasSetup 1///Called when UIView is removed as subview from superview#define __METHOD_MACRO_wasRemovedFromSuperview() \__INTERNAL_METHOD_MACRO__didChangeSuperviewsSetup() \-(void)__wasRemovedFromSuperview/*{ //perform extra processes here }*/#endif


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