The category implements a method that is also implemented in the main class: `viewWillAppear:`

Question

I am trying to switch the UIViewController category to viewWillAppear:. But getting this warning.

A category implements a method that is also implemented in a class

@implementation UIViewController (ViewWillAppearCategory)

-(void)viewWillAppear:(BOOL)animated
{
    //.........
}

@end

I want some things to appear on all screens while watching, so I don’t want to touch the whole screen . therefore, go with the category.

I can implement some method in a subclass, and I can call this method in all VCs (full screen). But I do not want this. It is automatically called up on the screen, a call will appear. Is it any idea to do this or make any mistake above?

. . . , . .

Answer 1

Method Swizzling, , .

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http://nshipster.com/method-swizzling/

Answer 2

, . , UIViewController, , MyUIViewController, :

-(void) viewWillAppear:(BOOL) animated {
    // do your "category" stuff
}

UIViewControllers MyUIViewController :

-(void) viewWillAppear:(BOOL) animated {
    [super viewWillAppear:animated];
    // rest of code for this class
}

Answer 3

, - :

• super , [super viewWillAppear:] .
• Swizzling - , , , , -.

, UIViewController, viewWillAppear:, :

• . / "".
• Nibs Storyboards.
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, . , , UINavigationControllerDelegate , .

---

viewWillAppear documentation:

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Answer 4

, , . , , UIViewController, viewWillAppear .

//UIViewController+CustomCategory.h
@interface UIViewConctroller (CustomCategory)

- (void)performCustomization;

@end

//UIViewController+CustomCategory.m
@implementation UIViewController (CustomCategory)

- (void)performCustomization {
    // Do custom stuff…
}

@end

//MYViewController.m
#import "UIViewController+CustomCategory.h"

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [self performCustomization];
}

Answer 5

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, ,

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"

-(void)viewWillAppear:(BOOL)animated
{
    NSLog(@"I get callback here too");
}

#pragma clang diagnostic pop

, , XCode.