Xcode UITapGestureReconizer错误

我的UITapGestureReconizer出现错误，如“UITapGestureReconizer未声明”。因为UITapGestureReconizer在一个具体类中，所以不应该声明它吗？我该如何修复它。。。下面是它第一次出现在代码中的地方

- (void)loadView {
    [super loadView];

    // set the tag for the image view
    [imageView setTag:ZOOM_VIEW_TAG];

    // add gesture recognizers to the image view
    UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTap:)];
    [imageView addGestureRecognizer:doubleTap];
    [doubleTap release];

    UITapGestureRecognizer *twoFingerTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTwoFingerTap:)];
    [imageView addGestureRecognizer:twoFingerTap];
    [twoFingerTap release];

    [doubleTap setNumberOfTapsRequired:2];
    [twoFingerTap setNumberOfTouchesRequired:2];

        // calculate minimum scale to perfectly fit image width, and begin at that scale
    float minimumScale = [imageScrollView frame].size.width  / [imageView frame].size.width;
    [imageScrollView setMinimumZoomScale:minimumScale];
    [imageScrollView setZoomScale:minimumScale];
}

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UITapGestureRecognizer

是UIKit的一部分，因此只要您在某处导入

，就应该声明它。但是，我在代码中看到的一个问题是：

UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTap:)];
[imageView addGestureRecognizer:doubleTap];
[doubleTap release];

…

[doubleTap setNumberOfTapsRequired:2];

在调用

[doubleTap setNumberOfTapsRequired:2]

时，您没有对

doubleTap

的有效引用。它很可能由

imageView

保留，但这是一个无法依赖的实现细节。在调用

-release

之前，将调用移动到

-setNumberOfTapsRequired:

，以确保这不会在未来版本的iOS中中断