UIButton+Category implementation override other UIButton's touch event

Question

I am using a opensource implementation of UIButton with extension so it is draggable.

Here's the header of this UIButton+NMCategory file:

#import <UIKit/UIKit.h>

@interface UIButton (NMCategory)

@property(nonatomic,assign,getter = isDragEnable)   BOOL dragEnable;
@property(nonatomic,assign,getter = isAdsorbEnable) BOOL adsorbEnable;

@end

and in it's implementation, it implements the onTouchesBegin , onTouchesMoved and onTouchesEnd interfaces, which all functioning OK and this button became draggable.

However, in the rest part of my project, there's another implementation of a draggable button been used. Here's the header of it:

@interface SEFilterKnob : UIButton

@end

And below is how it is been used:

[knob addTarget:self action:@selector(MyTouchDown:withEvent:) forControlEvents:UIControlEventTouchDown];
[knob addTarget:self action:@selector(MyTouchUp:) forControlEvents:UIControlEventTouchUpInside | UIControlEventTouchUpOutside];
[knob addTarget:self action:@selector(MyTouchMove:withEvent:) forControlEvents: UIControlEventTouchDragOutside | UIControlEventTouchDragInside];

When I apply the UIButton+NMCategory implementation to the whole project, the SEFilterKnob draggable button stopped working and I saw it's touch events are all routed to the UIButton+NMCategory touch event implementation. (its own selectors are not being called)

I am not familiar with Obj-C's category feature, can someone please help explain why this could happen? Thanks!

Answer 1

Unfortunately, you can't combine the two. Also, be very mindful about the destructive effects of the categories in Obj-C.

They modify ALL instances of the class and I'd definitely opted out for the good-old subclass. It's the safest and the right decision. Especially if you're experiencing conflicts.

Answer 2

In a category you normally tend to overwrite current methods.

From developer.apple.com : "When a category overrides an inherited method, the method in the category can, as usual, invoke the inherited implementation via a message to super. However, if a category overrides a method that already existed in the category's class, there is no way to invoke the original implementation"

If you like to call your old/overwritten method, you should try swizzling which is a powerful obj-c feature (and it's not a hack!).