- (Class)createClass:(NSString*)className{     NSString* kLXDkvoClassPrefix= @"NSKVONotifying_";    NSString * kvoClassName = [kLXDkvoClassPrefix stringByAppendingString: className];    Class observedClass = NSClassFromString(kvoClassName);    if (observedClass) { return observedClass; }    Class kvoClass = objc_allocateClassPair(NSClassFromString(className), kvoClassName.UTF8String, 0);    objc_registerClassPair(kvoClass);    return kvoClass;}