Switching on custom property to change image of MGLSymbolStyleLayer

问题

I have such enum which I'd like to assign to the pins, so that depending on this enum value, the pin image is different:

typedef NS_ENUM(NSInteger, MyType) {
    MyTypeUnknown = 0,
    MyTypeOne,
    MyTypeTwo,
};

I've got my layer for non-clustered pins:

MGLSymbolStyleLayer *markerLayer = [[MGLSymbolStyleLayer alloc] initWithIdentifier:@"markerLayerId" source:source];
markerLayer.predicate = [NSPredicate predicateWithFormat:@"cluster != YES"];
[style addLayer: markerLayer];

and I know I want to add various images based on type of the pin. The only thing I'm sure about is that I need to add those images to the layer:

[style setImage:[UIImage imageNamed:@"img0"] forName:@"img0id"];
[style setImage:[UIImage imageNamed:@"img1"] forName:@"img1id"];
[style setImage:[UIImage imageNamed:@"img2"] forName:@"img2id"];

Now I should set the name, but I'm not sure how:

markerLayer.iconImageName = [NSExpression expressionForConstantValue:@"???"]; // or withFormat..?

I've overridden their class to add my custom properties:

@objc class MyPointFeature: MGLPointFeature {
    @objc var type: MyType = .unknown
}

And I'm really lost how to switch on that type property to set the image of the pin. Any help please?

回答1:

Firstly we need to have a variable, which can be used for accessing the values. To make it most readable, let's create a variable for our needs (later, eg when selecting a pin) and the entry for MapBox needs at once:

@objc class MyPointFeature: MGLPointFeature {
    @objc var type: MyType = .unknown {
        didSet {
            self.attributes = ["myType": MyPointFeature .staticTypeKey(dynamicType: type)]
        }
    }

    // This is made without dynamic property name to string cast, because
    // the values shouldn't be changed so easily and a developer without
    // suspecting it's a key somewhere could accidentally create a bug
   // PS. if you have swift-only code, you can make it in MyType enum
   @objc static func staticTypeKey(dynamicType: MyType) -> String {
        switch dynamicType {
        case .one:
            return "one"
        case .two:
            return "two"
        default:
            return "unknown"
        }
    }
}

Now we want to register image names to given keys:

[style setImage:[UIImage imageNamed:@"img0"] forName:@"img0Key"];
[style setImage:[UIImage imageNamed:@"img1"] forName:@"img1Key"];
[style setImage:[UIImage imageNamed:@"img2"] forName:@"img2Key"];

Finally, let's bind the image name keys with assigned previously attribute:

NSDictionary *typeIcons = @{[MyPointFeature staticTypeKeyWithDynamicType:MyTypeUnknown]: @"img0Key",
                            [MyPointFeature staticTypeKeyWithDynamicType:MyTypeOne]: @"img1Key",
                            [MyPointFeature staticTypeKeyWithDynamicType:MyTypeTwo]: @"img2Key"};
myLayer.iconImageName = [NSExpression expressionWithFormat:@"FUNCTION(%@, 'valueForKeyPath:', myType)", typeIcons];

Obviously, key names should be wrapped in some constants etc, but refactoring is left for the reader, that's the simplest working solution.

来源：https://stackoverflow.com/questions/55144970/switching-on-custom-property-to-change-image-of-mglsymbolstylelayer

标签

ios

objective-c

swift

mapbox