How to delete whole blocks of NSAttributedString - ios

Question

I am working on an app that lets the user mention other users by typing #username. Though I have found a way to detect the # character and highlight the selected username within the text string, I am not sure how to manage the event when the user mentions a user but then wants to delete that user from the mention.
For example, in the Facebook app, when you mention someone, that person's name in the UITextView is highlighted with a light-blue background. However, when you start deleting that mention, the whole mention gets deleted when you delete the last character in the attributed string.
I am, therefore, looking for a way that I can capture when the user deletes the last character of an attributed string in order to delete that whole attributed string and completely remove the mention from the text view.

Answer 1

In order to achieve the desired behaviour mentioned above, I ended up doing the following. I implemented all these methods as part of the view controller where my UITextView is placed, so I added the UITextViewDelegate protocol to my view controller. Then, I implemented the following methods:
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
//if this is true, then the user just deleted a character by using backspace
if(range.length == 1 && text.length == 0){
NSUInteger cursorPosition = range.location; //gets cursor current position in the text
NSRange attrRange; //will store the range of the text that holds specific attributes
NSDictionary *attrs = [_content.attributedText attributesAtIndex:cursorPosition effectiveRange:&attrRange];
//check if the attributes of the attributed text in the cursor's current position correspond to what you want to delete as a block
if([attrs objectForKey:NSBackgroundColorAttributeName]){
NSAttributedString *newStr = [_content.attributedText attributedSubstringFromRange:NSMakeRange(0, attrRange.location)]; //creates a new NSAttributed string without the block of text you wanted to delete
_content.attributedText = newStr; //substitute the attributed text of your UITextView
return NO;
}
}
return YES;
}

Answer 2

Luis Delgado's excellent answer gave me a great jumping off point, but has a few shortcomings:
always clears to the end of the string
does not handle insertion into the token
does not handle modifying selected text that includes token(s)
Here is my version (Swift 4):
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
if range.location < textView.attributedText.length {
var shouldReplace = false
var tokenAttrRange = NSRange()
var currentReplacementRange = range
let tokenAttr = NSAttributedStringKey.foregroundColor
if range.length == 0 {
if nil != textView.attributedText.attribute(tokenAttr, at: range.location, effectiveRange: &tokenAttrRange) {
currentReplacementRange = NSUnionRange(currentReplacementRange, tokenAttrRange)
shouldReplace = true
}
} else {
// search the range for any instances of the desired text attribute
textView.attributedText.enumerateAttribute(tokenAttr, in: range, options: .longestEffectiveRangeNotRequired, using: { (value, attrRange, stop) in
// get the attribute's full range and merge it with the original
if nil != textView.attributedText.attribute(tokenAttr, at: attrRange.location, effectiveRange: &tokenAttrRange) {
currentReplacementRange = NSUnionRange(currentReplacementRange, tokenAttrRange)
shouldReplace = true
}
})
}
if shouldReplace {
// remove the token attr, and then replace the characters with the input str (which can be empty on a backspace)
let mutableAttributedText = textView.attributedText.mutableCopy() as! NSMutableAttributedString
mutableAttributedText.removeAttribute(tokenAttr, range: currentReplacementRange)
mutableAttributedText.replaceCharacters(in: currentReplacementRange, with: text)
textView.attributedText = mutableAttributedText
// set the cursor position to the end of the edited location
if let cursorPosition = textView.position(from: textView.beginningOfDocument, offset: currentReplacementRange.location + text.lengthOfBytes(using: .utf8)) {
textView.selectedTextRange = textView.textRange(from: cursorPosition, to: cursorPosition)
}
return false
}
}
return true
}
If you need to override a superclass, add the override keyword and instead of returning true at the end, return
super.textView(textView, shouldChangeTextIn: range, replacementText: text)
You can change tokenAttr to any standard or custom text attribute. If you change enumerateAttribute to enumerateAttributes, you could even look for a combination of text attributes.

Answer 3

If you already have the entire #username surrounded with an attribute, subclass UITextView and override -deleteBackward to check if the cursor is inside one of the username attributes. If not, just call the super implementation, otherwise find the starting location and the length of the attributed username and delete the entire range.