Swift 字符串范围 - 是否有更简单的方法来定义字符串范围？

Question

I consider if there are some easier ways to define string ranges I tried to use some function that need ranges and swift ranges seems to be incredibly unreadable and long.

title.startIndex..<title.index(title.startIndex, offsetBy: 1)

and just to say I want to search only in [0,1) characters of this string

label.text = title.replacingOccurrences(of: "\n", with: "", options: .caseInsensitive, range: title.startIndex..<title.index(title.startIndex, offsetBy: 1) )

Answer 1

There isn't really a concise way to specify a String range.

You could make it a bit nicer with an extension:

extension StringProtocol {
    func range(_ ir: Range<Int>) -> Range<String.Index> {
        return self.index(self.startIndex, offsetBy: ir.lowerBound) ..< self.index(self.startIndex, offsetBy: ir.upperBound)
    }
}

Then

title.startIndex..<title.index(title.startIndex, offsetBy: 1)

becomes

title.range(0..<1)

Note: Be careful to specify a valid range, or this will crash, just like if you had used an offset beyond the end of your string in your example.

Answer 2

The problem is that replacingOccurrencesOf is an Cocoa Objective-C NSString method, so you end up with type impedance mismatch between the String notion of a Range and the NSString notion of an NSRange. The simplest solution is to stay in the NSString world:

label.text = (title as NSString).replacingOccurrences(
    of: "\n", with: "", options: .caseInsensitive, 
    range: NSRange(location: 0, length: 2))

Otherwise I agree with vacawama's idea of an extension:

extension String {
    func range(_ start:Int, _ count:Int) -> Range<String.Index> {
        let i = self.index(start >= 0 ?
            self.startIndex :
            self.endIndex, offsetBy: start)
        let j = self.index(i, offsetBy: count)
        return i..<j
    }
    func nsRange(_ start:Int, _ count:Int) -> NSRange {
        return NSRange(self.range(start,count), in:self)
    }
}

Then you can say

label.text = title.replacingOccurrences(
    of: "\n", with: "", options: .caseInsensitive, 
    range: title.range(0,2))