NSString may not respond to append string

Question

I have a NSMutableString and I am trying to use appendString method. Though it works fine but every time I use it, I receive a warning NSString may not respond to append string. This is my code :

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{

    [soapResults appendString: string];        //soapResults is an NSMutableString in .h
}  

I know I am getting this warning because of NSString string but how to remove this warning?

Answer 1

self.soapResults=(NSMutableString *)[self.soapResults stringByAppendingString:string];

or

soapResults=(NSMutableString *)[soapResults stringByAppendingString:string];

OR

self.soapResults=(NSMutableString *)[[self.soapResults stringByAppendingString:string] mutableCopy];

    //    or

soapResults=(NSMutableString *)[[soapResults stringByAppendingString:string] mutableCopy];