setting NSAttributed String attribute overrides substring attributes - objective-c

Question

I have created a mutable string which will look like #"testMeIn:greenColor:Different:greencolor:Colors"
NSMutableAttributedString *mutableText = [[NSMutableAttributedString alloc] initWithAttributedString:myString];
UIColor *foregroundColor = [UIColor blackColor];
NSString *key = NSForegroundColorAttributeName;
[mutableText addAttribute:key value:foregroundColor range:NSMakeRange(0, myString.length)];
When I add Attribute foregroundColor , the existing green color in substring gets overridden by the specified black color. Though I can change the code to set the green color for substring, I would like to know is there any other way of applying styles to the part of Strings which doesn't have styles without overriding the existing styles.

Answer 1

You can enumerate over each attribute span in the string, and only change attributes if they are not already set
NSMutableAttributedString* aString =
[[NSMutableAttributedString alloc] initWithString:#"testMeIn DIFFERENT Colors"];
[aString setAttributes:#{NSForegroundColorAttributeName:[UIColor greenColor]}
range:(NSRange){9,9}];
[aString enumerateAttributesInRange:(NSRange){0,aString.length}
options:nil
usingBlock:
^(NSDictionary* attrs, NSRange range, BOOL *stop) {
//unspecific: don't change text color if ANY attributes are set
if ([[attrs allKeys] count]==0)
[aString addAttribute:NSForegroundColorAttributeName
value:[UIColor redColor]
range:range];
//specific: don't change text color if text color attribute is already set
if (![[attrs allKeys] containsObject:NSForegroundColorAttributeName])
[aString addAttribute:NSForegroundColorAttributeName
value:[UIColor redColor]
range:range];
}];