IOS：给@selector添加一个参数

当我有这行代码时

UILongPressGestureRecognizer *downwardGesture = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(dragGestureChanged:)];

and this

- (void)dragGestureChanged:(UILongPressGestureRecognizer*)gesture{
...
}

我想在“@selector(dragGestureChanged:)”处添加一个参数“(UIScrollView*)scrollView”，我该怎么办？

你不能直接——UIGestureRecognizer我们知道如何向仅接受一个参数的选择器发出调用。为了完全通用，您可能希望能够传递一个块。 Apple 尚未内置该功能，但添加起来相当容易，至少如果您愿意对手势识别器进行子类化，则可以解决添加新属性并在其后正确清理的问题，而无需深入研究运行时。

所以，例如（随我所写，未经检查）

typedef void (^ recogniserBlock)(UIGestureRecognizer *recogniser);

@interface UILongPressGestureRecognizerWithBlock : UILongPressGestureRecognizer

@property (nonatomic, copy) recogniserBlock block;
- (id)initWithBlock:(recogniserBlock)block;

@end

@implementation UILongPressGestureRecognizerWithBlock
@synthesize block;

- (id)initWithBlock:(recogniserBlock)aBlock
{
    self = [super initWithTarget:self action:@selector(dispatchBlock:)];

    if(self)
    {
         self.block = aBlock;
    }

    return self;
}

- (void)dispatchBlock:(UIGestureRecognizer *)recogniser
{
    block(recogniser);
}

- (void)dealloc
{
    self.block = nil;
    [super dealloc];
}

@end

然后你可以这样做：

UILongPressGestureRecognizer = [[UILongPressGestureRecognizerWithBlock alloc] 
        initWithBlock:^(UIGestureRecognizer *recogniser)
        {
            [someObject relevantSelectorWithRecogniser:recogniser 
                      scrollView:relevantScrollView];
        }];