MGLAnnotationView

@interface MGLAnnotationView : UIView <NSSecureCoding>

The MGLAnnotationView class is responsible for marking a point annotation with a view. Annotation views represent an annotation object, which is an object that corresponds to the MGLAnnotation protocol. When an annotation’s geographic coordinate is visible in the map view, the map view asks its delegate to a corresponding annotation view. If an annotation view is created with a reuse identifier, the map view may recycle the view when it goes offscreen.

Annotation views are compatible with UIKit, Core Animation, and other Cocoa Touch frameworks. On the other hand, if you do not need animation or interactivity such as dragging, you can use an MGLAnnotationImage instead to conserve memory and optimize drawing performance.

Initializing and Preparing the View

-initWithReuseIdentifier:

Initializes and returns a new annotation view object.

The reuse identifier provides a way for you to improve performance by recycling annotation views as they enter and leave the map’s viewport. As an annotation leaves the viewport, the map view moves its associated view to a reuse queue. When a new annotation becomes visible, you can request a view for that annotation by passing the appropriate reuse identifier string to the -[MGLMapView dequeueReusableAnnotationViewWithIdentifier:] method.

Declaration

Objective-C

- (nonnull instancetype)initWithReuseIdentifier:
(nullable NSString *)reuseIdentifier;

Swift

init(reuseIdentifier: String?)

Parameters

reuseIdentifier

A unique string identifier for this view that allows you to reuse this view with multiple similar annotations. You can set this parameter to nil if you don’t intend to reuse the view, but it is a good idea in general to specify a reuse identifier to avoid creating redundant views.

Return Value

The initialized annotation view object.

-initWithAnnotation:reuseIdentifier:

Initializes and returns a new annotation view object.

Providing an annotation allows you to explicitly associate the annotation instance with the new view and, in custom subclasses of MGLAnnotationView, customize the view based on properties of the annotation instance in an overridden initializer. However, annotation views that are reused will not necessarily be associated with the same annotation they were initialized with. Also, annotation views that are in the reuse queue will have a nil value for the annotation property. Passing an annotation instance to the view is optional and the map view will automatically associate annotations with views when views are provided to the map via the -[MGLMapViewDelegate mapView:viewForAnnotation:] method.

The reuse identifier provides a way for you to improve performance by recycling annotation views as they enter and leave the map’s viewport. As an annotation leaves the viewport, the map view moves its associated view to a reuse queue. When a new annotation becomes visible, you can request a view for that annotation by passing the appropriate reuse identifier string to the -[MGLMapView dequeueReusableAnnotationViewWithIdentifier:] method.

Declaration

Objective-C

- (nonnull instancetype)initWithAnnotation:
                        (nullable id<MGLAnnotation>)annotation
                       reuseIdentifier:(nullable NSString *)reuseIdentifier;

Parameters

annotation

The annotation object to associate with the new view.

reuseIdentifier

A unique string identifier for this view that allows you to reuse this view with multiple similar annotations. You can set this parameter to nil if you don’t intend to reuse the view, but it is a good idea in general to specify a reuse identifier to avoid creating redundant views.

Return Value

The initialized annotation view object.

-prepareForReuse

Called when the view is removed from the reuse queue.

The default implementation of this method does nothing. You can override it in your custom annotation view implementation to put the view in a known state before it is returned to your map view delegate.

Declaration

Objective-C

- (void)prepareForReuse;

Swift

func prepareForReuse()

annotation

The annotation object currently associated with the view.

You should not change the value of this property directly. This property contains a non-nil value while the annotation view is visible on the map. If the view is queued, waiting to be reused, the value is nil.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, nullable)
id<MGLAnnotation>
    annotation;

reuseIdentifier

The string that identifies that this annotation view is reusable.

You specify the reuse identifier when you create the view. You use the identifier later to retrieve an annotation view that was created previously but which is currently unused because its annotation is not on-screen.

If you define distinctly different types of annotations (with distinctly different annotation views to go with them), you can differentiate between the annotation types by specifying different reuse identifiers for each one.

Declaration

Objective-C

@property (nonatomic, readonly, nullable) NSString *reuseIdentifier;

Swift

var reuseIdentifier: String? { get }

Configuring the Appearance

centerOffset

The offset, measured in points, at which to place the center of the view.

By default, the center point of an annotation view is placed at the geographic coordinate point of the associated annotation. If you do not want the view to be centered, you can use this property to reposition the view. The offset’s dx and dy values are measured in points. Positive offset values move the annotation view down and to the right, while negative values move it up and to the left.

Set the offset if the annotation view’s visual center point is somewhere other than the logical center of the view. For example, the view may contain an image that depicts a downward-pointing pushpin or thumbtack, with the tip positioned at the center-bottom of the view. In that case, you would set the offset’s dx to zero and its dy to half the height of the view.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
CGVector centerOffset;

Swift

var centerOffset: CGVector { get set }

scalesWithViewingDistance

A Boolean value that determines whether the annotation view grows and shrinks as the distance between the viewpoint and the annotation view changes on a tilted map.

When the value of this property is YES and the map is tilted, the annotation view appears smaller if it is towards the top of the view (closer to the horizon) and larger if it is towards the bottom of the view (closer to the viewpoint). This is also the behavior of MGLAnnotationImage objects. When the value of this property is NO or the map’s pitch is zero, the annotation view remains the same size regardless of its position on-screen.

The default value of this property is NO. Keep this property set to NO if the view’s legibility is important.

Note

Scaling many on-screen annotation views can contribute to poor map performance. Consider keeping this property disabled if your use case involves hundreds or thousands of annotation views.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
BOOL scalesWithViewingDistance;

Swift

var scalesWithViewingDistance: Bool { get set }

rotatesToMatchCamera

A Boolean value that determines whether the annotation view rotates together with the map.

When the value of this property is YES and the map is rotated, the annotation view rotates. This is also the behavior of MGLAnnotationImage objects. When the value of this property is NO the annotation has its rotation angle fixed.

The default value of this property is NO. Set this property to YES if the view’s rotation is important.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
BOOL rotatesToMatchCamera;

Swift

var rotatesToMatchCamera: Bool { get set }

Managing the Selection State

selected

A Boolean value indicating whether the annotation view is currently selected.

You should not set the value of this property directly. If the property is set to YES, the annotation view is displaying a callout.

By default, this property is set to NO and becomes YES when the user taps the view. Selecting another annotation, whether it is associated with an MGLAnnotationView or MGLAnnotationImage object, deselects any currently selected view.

Setting this property changes the view’s appearance to reflect the new value immediately. If you want the change to be animated, use the -setSelected:animated: method instead.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, getter=isSelected)
BOOL selected;

Swift

var isSelected: Bool { get set }

-setSelected:animated:

Sets the selection state of the annotation view with an optional animation.

You should not call this method directly. A map view calls this method in response to user interactions with the annotation. Subclasses may override this method in order to customize the appearance of the view depending on its selection state.

Declaration

Objective-C

- (void)setSelected:(BOOL)selected animated:(BOOL)animated;

Swift

func setSelected(_ selected: Bool, animated: Bool)

Parameters

selected

YES if the view should display itself as selected; NO if it should display itself as unselected.

animated

YES if the change in selection state is animated; NO if the change is immediate.

Supporting Drag Operations

draggable

A Boolean value indicating whether the annotation view is draggable.

If this property is set to YES, the user can drag the annotation after pressing and holding the view, and the associated annotation object must also implement the -setCoordinate: method. The default value of this property is NO.

Setting this property to YES lets the map view know that the annotation is always draggable. In other words, you cannot conditionalize drag operations by attempting to stop an operation that has already been initiated; doing so can lead to undefined behavior. Once begun, the drag operation should always continue to completion.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, getter=isDraggable)
BOOL draggable;

Swift

var isDraggable: Bool { get set }

dragState

The current drag state of the annotation view.

All states are handled automatically when the draggable property is set to YES. To perform a custom animation in response to a change to this property, override the -setDragState:animated: method.

Declaration

Objective-C

@property (nonatomic, readonly) MGLAnnotationViewDragState dragState;

Swift

var dragState: MGLAnnotationViewDragState { get }

-setDragState:animated:

Sets the current drag state for the annotation view.

You can override this method to animate a custom annotation view as the user drags it. As the system detects user actions that would indicate a drag, it calls this method to update the drag state.

Declaration

Objective-C

- (void)setDragState:(MGLAnnotationViewDragState)dragState
        animated:(BOOL)animated;

Swift

func setDragState(_ dragState: MGLAnnotationViewDragState, animated: Bool)