MGLVectorStyleLayer

 

@interface MGLVectorStyleLayer : MGLForegroundStyleLayer

MGLVectorStyleLayer is an abstract superclass for style layers whose content is defined by an MGLShapeSource or MGLVectorSource object.

Create instances of MGLCircleStyleLayer, MGLFillStyleLayer, MGLFillExtrusionStyleLayer, MGLLineStyleLayer, and MGLSymbolStyleLayer in order to use MGLVectorStyleLayer‘s properties and methods. Do not create instances of MGLVectorStyleLayer directly, and do not create your own subclasses of this class.

Refining a Style Layer’s Content

  • Identifier of the layer within the source identified by the sourceIdentifier property from which the receiver obtains the data to style.

    Declaration

    Objective-C

    @property (assign, readwrite, nonatomic, nullable)
    NSString *sourceLayerIdentifier;

    Swift

    var sourceLayerIdentifier: String? { get set }
    View Source on GitHub

  • The style layer’s predicate.

    Use the style layer’s predicate to include only the features in the source layer that satisfy a condition that you define. If the style layer initially comes from the style, its predicate corresponds to the filter property in the style JSON.

    The following comparison operators are supported.

    • NSEqualToPredicateOperatorType (=, ==)
    • NSGreaterThanOrEqualToPredicateOperatorType (>=, =>)
    • NSLessThanOrEqualToPredicateOperatorType (<=, =<)
    • NSGreaterThanPredicateOperatorType (>)
    • NSLessThanPredicateOperatorType (<)
    • NSNotEqualToPredicateOperatorType (!=, <>)
    • NSBetweenPredicateOperatorType (BETWEEN)

    The following compound operators are supported:

    • NSAndPredicateType (AND, &&)
    • NSOrPredicateType (OR, ||)
    • NSNotPredicateType (NOT, !)

    The following aggregate operators are supported:

    • NSInPredicateOperatorType (IN)
    • NSContainsPredicateOperatorType (CONTAINS)

    To test whether a feature has or lacks a specific attribute, compare the attribute to NULL or NIL. Predicates created using the +[NSPredicate predicateWithValue:] method are also supported. String operators and custom operators are not supported.

    For details about the predicate format string syntax, consult the “Predicate Format String Syntax” chapter of the “Predicate Programming Guide” in Apple developer documentation.

    The predicate’s left-hand expression must be a string that identifies a feature attribute or, alternatively, one of the following special attributes:

    AttributeMeaning
    $id A value that uniquely identifies the feature in the containing source. For details on the types of values that may be associated with this key, consult the documentation for the MGLFeature protocol’s identifier property.
    $type The type of geometry represented by the feature. A feature’s type is guaranteed to be one of the following strings:
    • Point for point features, corresponding to the MGLPointAnnotation class
    • LineString for polyline features, corresponding to the MGLPolyline class
    • Polygon for polygon features, corresponding to the MGLPolygon class
    point_count The number of point features in a given cluster.

    The predicate’s right-hand expression must be an NSString (to match strings) or NSNumber (to match numbers, including Boolean values) or an array of NSStrings or NSNumbers, depending on the operator and the type of values expected for the attribute being tested. For floating-point values, use -[NSNumber numberWithDouble:] instead of -[NSNumber numberWithFloat:] to avoid precision issues.

    Automatic type casting is not performed. Therefore, a feature only matches this predicate if its value for the attribute in question is of the same type as the value specified in the predicate. Also, operator modifiers such as c (for case insensitivity), d (for diacritic insensitivity), and l (for locale sensitivity) are unsupported for comparison and aggregate operators that are used in the predicate.

    It is possible to create expressions that contain special characters in the predicate format syntax. This includes the $ in the $id and $type special style attributes and also hyphen-minus and tag:subtag. However, you must use %K in the format string to represent these variables: @"%K == 'LineString'", @"$type".

    Example

    To filter the layer to include only the features whose index attribute is 5 or 10 and whose ele attribute is at least 1,500, you could create an NSCompoundPredicate along these lines:

    let layer = MGLLineStyleLayer(identifier: "contour", source: terrain)
layer.sourceLayerIdentifier = "contours"
layer.predicate = NSPredicate(format: "(index == 5 || index == 10) && ele >= 1500.0")
mapView.style?.addLayer(layer)

    Declaration

    Objective-C

    @property (assign, readwrite, nonatomic, nullable) NSPredicate *predicate;

    Swift

    var predicate: NSPredicate? { get set }
    View Source on GitHub