Add attributes to NSMutableAttributedString character by character - ios

Question

Here's my situation:
I have an NSMutableAttributedString with no attributes in a text view. Whenever the user presses the backspace key, I do not want a character to be deleted, I want it to be struck through, just like the "Track Changes" feature of productivity suites. I want the user to be able to continue typing normally after that. Here's how I started out:
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
if (text.length == 0 && textView.text.length == 0) return YES;
if (text.length == 0 && !([[textView.text substringFromIndex:textView.text.length - 1] isEqualToString:#" "] || [[textView.text substringFromIndex:textView.text.length - 1] isEqualToString:#"\n"])) {
textView.attributedText = [self strikeText:textView.attributedText];
textView.selectedRange = NSMakeRange(textView.attributedText.length - 1, 0);
return NO;
}
return YES;
}
- (NSAttributedString *)strikeText:(NSAttributedString *)text
{
NSRange range;
NSMutableAttributedString *returnValue = [[NSMutableAttributedString alloc] initWithAttributedString:text];
if (![text attribute:NSStrikethroughStyleAttributeName atIndex:text.length - 1 effectiveRange:&range]) {
NSLog(#"%#", NSStringFromRange(range));
NSLog(#"%#", [text attribute:NSStrikethroughStyleAttributeName atIndex:text.length - 1 effectiveRange:&range]);
[returnValue addAttribute:NSStrikethroughStyleAttributeName value:#(NSUnderlineStyleSingle) range:NSMakeRange(text.length - 1, 1)];
[returnValue addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(text.length - 1, 1)];
}
else {
[returnValue addAttribute:NSStrikethroughStyleAttributeName value:#(NSUnderlineStyleSingle) range:NSMakeRange(range.location - 1, 1)];
[returnValue addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(range.location - 1, 1)];
}
[returnValue removeAttribute:NSStrikethroughStyleAttributeName range:NSMakeRange(returnValue.length, 1)];
return returnValue;
}
However, no matter how hard I think, I can't wrap my head around the situation. This code doesn't work, or works partially. The value returned by attribute: atIndex: effectiveRange: is always nil, doesn't matter if the attribute actually exists or not. The effective range is out of bounds of the text I have.
Please help me out here.

Answer 1

In your strikeText: method you're only checking the very end of your attributedString. If you want to check the last character you should check from text.length -2, assuming that text is long enough. Also you're removeAttribute in the end of the method does not make much sense too me.
A simple approach on how you can reuse the range from the Delegate-Protocol to strike only the characters you need:
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
// check if your replacement is going to be empty, therefor deleting
if ([text length] == 0) {
// don't strike spaces and newlines, could use NSCharacterSet here
NSString *textToDelete = [textView.text substringWithRange:range];
if (![#[ #" ", #"\n" ] containsObject:textToDelete]) {
textView.attributedText = [self textByStrikingText:textView.attributedText inRange:range];
}
textView.selectedRange = NSMakeRange(range.location, 0);
return NO;
}
return YES;
}
- (NSAttributedString *)textByStrikingText:(NSAttributedString *)text inRange:(NSRange)range
{
NSMutableAttributedString *strickenText = [[NSMutableAttributedString alloc] initWithAttributedString:text];
[strickenText addAttribute:NSStrikethroughStyleAttributeName value:#(NSUnderlineStyleSingle) range:range];
[strickenText addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:range];
return strickenText;
}
There might be more edge cases but this is a simple approach that does what you want.

Answer 2

You should try:
NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithString:#"Hello. That is a test"];
[str addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:22] range:NSMakeRange(2,1)];
[str addAttribute:NSForegroundColorAttributeName value:[UIColor greenColor] range:NSMakeRange(8,2)];
[str addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(18,2)];
And attributes are described here:
https://developer.apple.com/documentation/foundation/nsattributedstringkey?language=objc