Replace hardcoded value to dynamic value

Dynamic Predicate

NSString *contextString = @"userName";
NSString *searchText = @"sh";

NSString *predicateString = [NSString stringWithFormat:@"%@ CONTAINS[c]", contextString];
      predicateString = [predicateString stringByAppendingString:@"%@"];
      NSPredicate *predicate = [NSPredicate predicateWithFormat:predicateString,searchText];
      NSArray *filteredArray = [refArray filteredArrayUsingPredicate:predicate];
      
                                          OR
Below code crash if searchText = @""
contextString = [contextString stringByAppendingString:@" CONTAINS[c] %@"];// white space is manditory at begining of appended
      NSPredicate *predicate = [NSPredicate predicateWithFormat:contextString, searchText];
      NSArray *filteredArray = [refArray filteredArrayUsingPredicate:predicate];