Setting foreground color works only once for NSAttributedString

问题

The phone part of the string gets the underline attribute, but the color remains red. I've separated the color and underline setAttributes() calls, to make things clear, the same happens when it's one call.

    let text = "call "
    let phone = "1800-800-900"

    let attrString = NSMutableAttributedString(string: text + phone, attributes: nil)
    let rangeText = (attrString.string as NSString).range(of: text)
    let rangePhone = (attrString.string as NSString).range(of: phone)

    attrString.setAttributes([NSAttributedStringKey.foregroundColor: UIColor.red],
                             range: rangeText)

    attrString.setAttributes([NSAttributedStringKey.foregroundColor: UIColor.blue],
                             range: rangePhone)

    attrString.setAttributes([NSAttributedStringKey.underlineStyle: NSUnderlineStyle.styleSingle.rawValue],
                             range: rangePhone)

回答1:

From the doc of setAttributes():

These new attributes replace any attributes previously associated with the characters in aRange.

So in other words, it replace them, erasing all previously set, so when you add the underline, it removes the color at that range.

Solution, use addAttributes() instead of setAttributes():

let text = "call "
let phone = "1800-800-900"

let attrString = NSMutableAttributedString(string: text + phone, attributes: nil)
let rangeText = (attrString.string as NSString).range(of: text)
let rangePhone = (attrString.string as NSString).range(of: phone)

attrString.addAttributes([NSAttributedStringKey.foregroundColor: UIColor.red],
                         range: rangeText)

attrString.addAttributes([NSAttributedStringKey.foregroundColor: UIColor.blue],
                         range: rangePhone)

attrString.addAttributes([NSAttributedStringKey.underlineStyle: NSUnderlineStyle.styleSingle.rawValue],
                         range: rangePhone)

Other solution, use two NSAttributedString (I also remove the NSAttributedStringKey in the enum)

let textAttrStr = NSAttributedString(string:text, attributes:[.foregroundColor: UIColor.red])
let phoneAttrStr = NSAttributedString(string:phone, attributes:[.foregroundColor: UIColor.blue,
                                                               .underlineStyle: NSUnderlineStyle.styleSingle.rawValue])

let finalAttrStr = NSMutableAttributedString.init(attributedString: textAttrStr)
finalAttrStr.append(phoneAttrStr)

Possible issue with the first solution:
range(of:) returns the range of the first occurence only. In other words, if text = "1800 " and phone = "18", you'll get unwanted results. because rangePhone would be from index 0 to 1, and not 7 to 8 in 1800 18. This issue won't happen in the second one.

回答2:

You should not separate the second and the third call of setAttributes, since the latter will overwrite the earlier. Combine the styles in one array:

attrString.setAttributes([.foregroundColor: UIColor.blue,
                          .underlineStyle: NSUnderlineStyle.styleSingle.rawValue],
                          range: rangePhone)

Result:

来源：https://stackoverflow.com/questions/48318561/setting-foreground-color-works-only-once-for-nsattributedstring

标签

swift

nsattributedstring