iPhone iOS UITapGestureRecognizer是否可以用某个接触点初始化识别器？

Question

I'm using a tap gesture recognizer to position a little subview with a label within another UIView. When the user taps on a view, the label is populated with the title of the component that the user tapped on, and the subview is centered at the tap location.

I need to make sure that the initial position of my gesture recognizer matches the center of the subview as defined in the storyboard(before the user taps on a view), but it seems that I'm unable to find a way to pass this point over to the gesture recognizer. Is there a way to initialize my tap gesture recognizer with a certain point within a view?

Answer 1

I'm not quite sure what you are asking. Gesture Recognizes do not have a "starting point". They receive various touch types for touches inside of a given view and allow you to uniquely handle each one.

If you want to simulate a touch on loading (which sort of sounds like that might be what you are looking to do), reorganize your code to be something like this:

- (void)viewDidLoad
{
     //simulate touch here
     [self touchedAtLocation:CGPointMake(100, 100)];
}

//Your delegate method
- (void)handleTap:(UITapGestureRecogizer *)recognizer
{
    [self touchedAtLocation:[recognizer locationInView:self.view]];
}

- (void)touchedAtLocation:(CGPoint)location
{
    //perform action based on location of touch
}

In this example, you could start the position/data of your subview based on what it would be if there was a touch at 100,100.

Note: I left out code configuring your gesture recognizer because it sounds like you already have that part under control. If not, I can post with more code.

Answer 2

A couple things that might help:

Gesture recognizers can be attached to any view in the view hierarchy. So if you want some small sub-sub-view to recognize the tap, you can addGestureRecognizer to that view.

When the gesture is recognized, you can test the gesture's location (and other aspects of it's state) before deciding to do anything about it. For example, let's say you only want the gesture to work if the user taps a very small space inside of a view...

- (void)handleTap:(UITapGestureRecogizer *)recognizer {

    // get the location relative to the subview to which this recognizer is attached
    CGPoint location = [recognizer locationInView:recognizer.view];

    // tiny rect to test, also in the recognizer's view's coordinates
    CGRect someSmallerRect = CGRectInset(recognizer.view.bounds, 10, 10);

    if (CGRectContainsPoint(someSmallerRect, location)) {
        // do whatever the touch should do
    }
    // otherwise, it's like it never happened
}