How do I find the last occurrence of a substring in a Swift string?

Question

In Objective-C I used:

[@"abc def ghi abc def ghi" rangeOfString:@"c" options:NSBackwardsSearch];

But now NSBackWardsSearch seems not to exist. Could anyone provide equivalent code for Swift?

I would like to be able to find the character number in the whole string if possible. So in the example above it would return 3.

Answer 1

And if you want to replace the last substring in a string:

(Swift 3)

extension String
{
    func replacingLastOccurrenceOfString(_ searchString: String,
            with replacementString: String,
            caseInsensitive: Bool = true) -> String
    {
        let options: String.CompareOptions
        if caseInsensitive {
            options = [.backwards, .caseInsensitive]
        } else {
            options = [.backwards]
        }

        if let range = self.range(of: searchString,
                options: options,
                range: nil,
                locale: nil) {

            return self.replacingCharacters(in: range, with: replacementString)
        }
        return self
    }
}

Usage:

let alphabet = "abc def ghi abc def ghi"
let result = alphabet.replacingLastOccurrenceOfString("ghi",
        with: "foo")

print(result)

// "abc def ghi abc def foo"

Or, if you want to remove the last substring completely, and clean it up:

let result = alphabet.replacingLastOccurrenceOfString("ghi",
            with: "").trimmingCharacters(in: .whitespaces)

print(result)

// "abc def ghi abc def"

Answer 2

Cocoa frameworks should be accessible in Swift, but you need to import them. Try importing Foundation to access the NSString API. From " Working with Cocoa Data Types–Strings " of the "Using Swift with Cocoa and Objective-C" guide:

Swift automatically bridges between the String type and the NSString class. [...] To enable string bridging, just import Foundation.

Additionally, NSBackwardsSearch is an enum value (marked & imported as an option ), so you have to use Swift's enum/option syntax to access it (as part of the NSStringCompareOptions option type). Prefixes are stripped from C enumeration values, so drop the NS from the value name.

Taken all together, we have:

import Foundation
"abc def ghi abc def ghi".rangeOfString("c", options:NSStringCompareOptions.BackwardsSearch)

Note that you might have to use the distance and advance functions to properly make use of the range from rangeOfString .

Answer 3

斯威夫特 3.0：

"abc def ghi abc def ghi".range(of: "c", options: String.CompareOptions.backwards, range: nil, locale: nil)

Answer 4

斯威夫特 5：

"abc def ghi abc def ghi".range(of: "c", options: NSString.CompareOptions.backwards)