How I can migrate from `MGLConstantStyleValue` to `NSExpression`

Question

I'm trying to migrate from mapbox-sdk-3.7 to mapbox-sdk-4.0.

I can't understand how to convert this syntax with MGLConstantStyleValue to NSExpression.

let layer = style.layer(withIdentifier: "milestones") as? MGLSymbolStyleLayer
let styledValues: [String: MGLStyleValue<NSString>] = ...

layer.iconImageName = MGLConstantStyleValue(interpolationMode: .identity,
                    sourceStops: styledValues,
                    attributeName: "imageId")

score 3 · Accepted Answer · edited Apr 21 '18 at 01:53

Identity interpolation mode uses the value for a feature attribute as a style value. Therefore, a stops dictionary should be unnecessary. In the case you outlined, looked like it used the value for imageId.

With NSExpression, you may want to try layer.iconImageName = NSExpression(forKeyPath: "imageId")

If you would like a stops dictionary to be taken to account, you may want to consider using MGL_MATCH, which takes an initial condition, this is followed by possible matches for that key and a corresponding value to assign to the layer property if there is a match. The final argument can be a default style value that is to be used if none of the specified values match.

layer.iconImageName = NSExpression(format: "MGL_MATCH(imageID, 'imageID1', 'nameForImageID1', 'defaultImageName')")

You may find these guides helpful:

How I can migrate from `MGLConstantStyleValue` to `NSExpression`

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