在ui滚动视图内的uiImageView中检测taps

我有一个uiscrollview,其中包含多个uiimageview,它是这样创建的。

frame = [[UIImageView alloc] initWithImage:bg];
frame.frame = CGRectMake(FRAME_SEPARATOR + numPage*1024 + numColumn*(FRAME_SEPARATOR+230), 10 +numRow*(FRAME_SEPARATOR+145), 230, 145);
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageTapped:)];
[frame addGestureRecognizer:tap];
[tap release];
[scroll addSubView:frame];

问题是,当点击图像时,不会调用ImageTapped。

如果我像这样将手势识别器添加到滚动视图中:

UITapGestureRecognizer *tap =
[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageTapped:)];
[scroll addGestureRecognizer:tap];
[tap release];

调用ImageTapped。

如何检测uiImageView上的taps?

谢谢