iOS 11/12/13/14/15 Map View Clustering Bugs

Bug Report ID

FB5438133

Affects: Xcode 9 through Xcode 13.3 (iOS 15)

Screenshot

Selected annotation should remain visible (should never be clustered)

Steps to reproduce

• launch the sample app
  • all annotations have the same clusteringIdentifier
  • all annotations have the same displayPriority
• tap on the "Under the Sea" annotation
  • expected and actual results
    • user sees the annotation view become selected
    • logs show that the annotation is selected
• zoom out just enough for the "Under The Sea" annotation to collide with the "Seven Dwarfs Mine Train" annotation
  • here's what I assume should happen, but does not happen
    • the "Under the Sea" annotation remains visible (and selected).
    • the "Seven Dwarfs Mine Train" annotation hides.

From the user's perspective, a selected annotation should always be visible regardless of the clustering identifier and display priority.

Selecting an annotation that is currently within a cluster should be become visible

Steps to reproduce

• launch the sample app

  • all annotations have the same clusteringIdentifier
  • all annotations have the same displayPriority

• ensure no annotations are currently selected

• zoom out just enough for the "It's a Small World", "Under the Sea", and "Seven Dwarfs Mine Train" annotations cluster together.

  • expected results and actual results
    • a cluster annotation appears showing "3"
      • cluster contains the "It's a Small World", "Under the Sea", and "Seven Dwarfs Mine Train" annotations

• tap the "Select" toolbar button to select the "It's a Small World" annotation

• here's what I assume should happen, but does not happen

  • the "It's A Small World" annotation view becomes and and is selected
  • the "Under The Sea" and "Seven Dwarfs Mine Train" annotation views may or may not be visible based on MapKit clustering/ zoom level logic.

  From the user's perspective, selecting an annotation that is currently part of a cluster should become visible regardless of the clustering identifier and display priority. It's possible, for example, for a user to select an annotation from a table view (or as in this hack example, a toolbar button).

  Here's a real scenario (similar to the Maps app)

  • tap a cluster annotation containing the "It's a Small World", "Under the Sea", and "Seven Dwarfs Mine Train" annotations
  • app displays a table view showing additional details about the rides
  • user taps a table view row to select the "Under the Sea" annotation
  • the selected "Under the Sea" annotation is automatically removed from the cluster

Other Notes

I have tried various ways to work around the issues. My workarounds either just don't work, or cause MapKit to crash.

Things I tried that I thought might work, but did not work:

• setting the selected annotation view clusteringIdentifier to nil.
  • this usually ends up crashing MapKit.
• setting the selected annotation's displayPriority to .required (while all other annotations had a lower priority).

In Summary

From the user's perspective, the selected annotation is the most important annotation. Therefore, MapKit should automatically ensure that the selected annotation is always visible regardless of the clusteringIdentifier, displayPriority, etc.

Also, it would help if the MapKit API was documented with details on how the API should be used. For example, tell us when it is safe to set the clusteringIdentifier and displayPriority. Give us examples of when and why we would want to create a MKClusterAnnotation subclass and implement the mapView(_:, clusterAnnotationForMemberAnnotations :) -> MKClusterAnnotation.