CODEWITHSUNDEEP
iosobjective-c
zerojian
zerojian

Reputation: 43

How to SuperClass object cast to SubClass [objective -c]

I want to add polyLine to mapView , the baidu mapView polyline superclass is BMKPolyLine, it have a class method:

+ (BMKPolyline *)polylineWithPoints:(BMKMapPoint *)points count:(NSUInteger)count;

I creat a subclass BKMyPolyLine, i add a @property colorString

when I get points and used superclass method :

BKMyPolyLine *myLine = [BKMyPolyLine polylineWithPoints:points count:points.count];

myLine.colorString = colorString;

and crash message:

[BMKPolyline setColorString:]: unrecognized selector sent to instance 0x138266fe0'

Upvotes: 1

Views: 180

Answers (1)

andyvn22
andyvn22

Reputation: 14824

This isn't "casting" (casting merely informs the compiler; it does not alter actual types)--but you have done something that should return your subclass. It sounds like BMKPolyline's +polylineWithPoints:count: method returns a BMKPolyline, even when it's called on a subclass. Instead you need to override what's known as the "designated initializer", which should be marked in the documentation. But from what I see online, it isn't documented--you probably (annoyingly) need to look into the source of BMKPolyline to know how to proceed.

Upvotes: 1

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