UIView，如何确定何时触摸进入视图

Question

It appears that all the touch methods of a UIView are only called if the touches began within the bounds of that view. Is there a way to have a view respond to a user who has touched outside the view, but then dragged his fingers into the view?

In case it matters, my specific application is for dragging a MKPinAnnotationView (using built-in 4.0 dragging). I want something to happen if the user drags a pin onto another view (which happens to be an AnnotationView as well, but it could be anything). No method for dragging is called until I let go of the pin; and no method no the UIView that's being dragged to seems to be called unless I started by touching from within the view.

Because the superview is a MKMapView, it is difficult to just use the touchesMoved event of that and check if the user is in the right location or not. Thanks!

Answer 1

So after playing around with it for a while, I found that the answer given here actually gave me what I needed, even though the question being asked was different.

It turns out you can subclass UIGestureRecognizer; and have it handle all the touches for the view that it has been added to (including an MKMapView). This allows all the normal MKMapView interactions to still behave without any problem; but also alerts me of the touches. In touchesMoved, I just check the location of the touch; and see if it is within the bounds of my other view.

From everything I tried; this seems to be the only way to intercept touchesMoved while the user is dragging an MKAnnotation.

Answer 2

You sure can:

(HitstateView.h)

#import <UIKit/UIKit.h>


@interface HitstateView : UIView {
    id overrideObject;
}

@property (nonatomic, retain) id overrideObject;

@end

(HitstateView.m)

#import "HitstateView.h"


@implementation HitstateView

@synthesize overrideObject;

- (void)dealloc {
    self.overrideObject = nil;

    [super dealloc];
}

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    UIView *hitView = [super hitTest:point withEvent:event];
    if (hitView == self) {
        return overrideObject;
    }
    return hitView;
}

@end

Make this view the size of your touch area. Set the overideObject to the view you want the touches to go. IIRC it ought to be a subview of the HitstateView.

Answer 3

Every view inherits UIResponder so every view gets touchesBegan/Moved/Ended - I do not think starting the touch outside the view means the view gets no event when the touch moves over the view. If you want to get a notification that something has been dragged onto your MKMapView you should make a subclass that handles the touch but then passes the event to super , allowing the hierarchy to do whatever it needs to do with the touch. You don't need to capture or modify the event just observe it.

Answer 4

It depends on how your views are set up. Generally leveraging the responder chain is the best way to go. It allows you to play tricks, though it may be too specific to address your particular needs.

You can also play tricks with forward events by override hit testing:

http://developer.apple.com/library/ios/#documentation/EventHandling/Conceptual/EventHandlingiPhoneOS/MultitouchEvents/MultitouchEvents.html%23//apple_ref/doc/uid/TP40009541-CH3-SW3

Your particular case sounds pretty exotic, so you may have to play tricks like having a parent view whose frame is large enough to contain both views in question.