How to properly swizzle UIScrollView with 3D touch peek pop?

Question

I'm trying to swizzle the UIScrollView that 3D Touch's peek and pop preview is embedded in. (I know it's a UIScrollView through the Reveal app.)

I want to know whenever the user moves their finger on this scroll view/on the 3D touch preview.

I tried swizzling it as follows:

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(setContentOffset:);
        SEL swizzledSelector = @selector(xxx_setContentOffset:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        BOOL didAddMethod =
        class_addMethod(class,
                        originalSelector,
                        method_getImplementation(swizzledMethod),
                        method_getTypeEncoding(swizzledMethod));

        if (didAddMethod) {
            class_replaceMethod(class,
                                swizzledSelector,
                                method_getImplementation(originalMethod),
                                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

#pragma mark - Method Swizzling

- (void)xxx_setContentOffset:(CGPoint)offset {
    [self xxx_setContentOffset:offset];

    NSLog(@"yes");

}

But it only calls "yes" once or twice when there should be hundreds of calls from sliding my finger across the screen.

Am I swizzling this wrong?

Answer 1

I am not sure that the scroll view itself calls the "setter" therefor you will not necessarily get the callback.

I created a "floating" view in the scrollview through KVO on the contentOffset property and it is called as expected. You may be able to use the same mechanism in your case:

        /**
         *  We are using KVO to offset the background image view
        */

        [self addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"contentOffset"]) {
        _bgImageView.frame = CGRectMake(self.contentOffset.x,0, self.frame.size.width, self.frame.size.height);
    }
}

but for reference I am swizzling like this:

+(void)load {
    NSArray *selectors = @[NSStringFromSelector(@selector(setText:)),...];

    for (NSString *name in selectors) {
        SEL originalSelector = NSSelectorFromString(name);
        SEL swizzledSelector = NSSelectorFromString([NSString stringWithFormat:@"iio_swizzled_%@",name]);
        Method originalMethod = class_getInstanceMethod(self, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
        class_addMethod(self,
                        originalSelector,
                        class_getMethodImplementation(self, originalSelector),
                        method_getTypeEncoding(originalMethod));
        class_addMethod(self,
                        swizzledSelector,
                        class_getMethodImplementation(self, swizzledSelector),
                        method_getTypeEncoding(swizzledMethod));
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }

}

-(void)iio_swizzled_setText:(NSString *)text {
   ... do stuff
   // and if needed to call the original 
  [self iio_swizzled_setText:text];
}