Preventing annotation deselection in MKMapView

问题

I have a situation in my app where I want to disable annotation deselection (other than when selecting another), so when I tap anywhere that is not an annotation view, it should leave the currently selected annotation as is. If I tap on another annotation view, it should select that one and deselect the other.

I was hoping to find something along the lines of a willDeselectAnnotationView in the MKMapViewDelegate or an isDeselected in MKAnnotationView, but there's unfortunately no such thing. I also tried overriding deselectAnnotation in a custom subclass of MKMapView, but it seems the tap triggered deselect doesn't invoke that function.

Is it possible to disable annotation deselection while preserving the ability to select? Thanks!

回答1:

I've found a way to do it! Make a boolean named something like "allowSelectionChanges", which I just have as global for now. Then use a subclass of MKMapView with this overriden function inside:

override func gestureRecognizerShouldBegin(gestureRecognizer: UIGestureRecognizer) -> Bool {
        return allowSelectionChanges
    } 

Switch this variable to false whenever you want to prevent annotation selection and deselection. It won't affect the user's ability to move around the map!

---

Here's an example of how this can be used to stop a callout from getting deselected when you tap on it to interact with it. Put this in your MKAnnotationView subclass:

override func pointInside(point: CGPoint, withEvent event: UIEvent?) -> Bool {
        let rect = self.bounds
        var isInside = CGRectContainsPoint(rect, point)
        if !isInside {
            for view in self.subviews {
                isInside = CGRectContainsPoint(view.frame, point)
                if isInside {
                    allowSelectionChanges = false
                    return true
                }
            }
            allowSelectionChanges = true
        }

        return false
    }

回答2:

Ok... I had this issue myself and while @clinton's answer pointed me in the right direction I came up with a solution that doesn't require your MKAnnotationView subclass to know about the mapView's custom property.

Here's my solution written for Swift 3:

public class <#CustomMapViewClass#>: MKMapView {

    private var allowSelectionChanges: Bool = true

    public override func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        return allowSelectionChanges
    }

    public override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        let pointInside = super.point(inside: point, with: event)
        if !pointInside {
            return pointInside
        }

        for annotation in annotations(in: visibleMapRect) where annotation is <#CustomAnnotationViewClass#> {
            guard let view = self.view(for: annotation as! MKAnnotation) else {
                continue
            }
            if view.frame.contains(point) {
                allowSelectionChanges = true
                return true
            }
        }
        allowSelectionChanges = false

        return pointInside
    }

}

回答3:

I'm basing my work off of @clinton and @mihai-fratu. Both of them gave very good answers so you should up-vote them as well. What I want to add is that if the tapped annotation is in a cluster, or if it is disabled, then you will still get the deselection happening. This is my code to attempt to fix that.

public class <#CustomMapViewClass#>: MKMapView {

    private var allowSelectionChanges: Bool = true

    public override func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        return allowSelectionChanges
    }

    public override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        let pointInside = super.point(inside: point, with: event)
        if pointInside {
            // Go through all annotations in the visible map rect
            for annotation in annotations(in: visibleMapRect) where annotation is MKAnnotation {
                // get the view of each annotation
                if let view: MKAnnotationView = self.view(for: annotation as! MKAnnotation) {
                    // work with the cluster view if there is one
                    let rootView = view.cluster ?? view
                    // If the frame of this view contains the selected point, then we are an annotation tap. Allow the gesture...
                    if (rootView.frame.contains(point)) {
                        allowSelectionChanges = rootView.isEnabled  // But only if the view is enabled
                        return pointInside
                    }
                }
            }
            // If you did not tap in any valid annotation, disallow the gesture
            allowSelectionChanges = false
        }
        return pointInside
    }
}

来源：https://stackoverflow.com/questions/34835499/preventing-annotation-deselection-in-mkmapview