objective-c - 是否可以从委托(delegate)调用原始委托(delegate)？

Question

出于好奇，是否可以在自定义委托(delegate)实现中调用原始委托(delegate)方法实现。像[ super 委托(delegate)方法]；或者说这是不可能的。在某些情况下，如果满足某些条件，我希望添加自定义行为。预先感谢您!

Answer 1

是的，这可以通过包装器对象来实现，该包装器对象拦截消息并将它们转发到另一个委托(delegate)对象。以下类会拦截对scrollViewDidScroll: 方法的调用，然后将其(以及任何其他委托(delegate)方法调用)转发到另一个 UIScrollViewDelegate。

@import UIKit;

@interface ScrollHandler : NSObject <UIScrollViewDelegate>
- (instancetype)initWithScrollViewDelegate:(id<UIScrollViewDelegate>)delegate;
@end

@implementation ScrollHandler {
    id<UIScrollViewDelegate> _scrollViewDelegate;
}

- (instancetype)initWithScrollViewDelegate:(id<UIScrollViewDelegate>)delegate {
    self = [super init];
    if (self) {
        _scrollViewDelegate = delegate;
    }
    return self;
}

// Intercept specific method invocations:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    // Implement custom behavior here before forwarding the invocation to _scrollViewDelegate
    [_scrollViewDelegate scrollViewDidScroll:scrollView];
}

// Forward unintercepted method invocations:

- (BOOL)respondsToSelector:(SEL)selector
{
    // Ask _scrollViewDelegate if it responds to the selector (and ourself as well)
    return [_scrollViewDelegate respondsToSelector:selector] || [super respondsToSelector:selector];
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
    // Forward the invocation to _scrollViewDelegate
    [invocation invokeWithTarget:_scrollViewDelegate];
}

@end

使用示例:

_scrollView = [[ScrollHandler alloc] init];
_scrollController = [[ScrollHandler alloc] initWithScrollViewDelegate:self];
_scrollView.delegate = _scrollController;