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苹果的老六行为

苹果有时候还是很老六的。比如在系统声音设置中，有一个声音叫“Heroine”，也就是女英雄。

lao6

那么如果你想在自己的应用中使用它，可以通过NSSound调用

class Foo {
    private var sound: NSSound?
    
    func playSound() {
        sound = NSSound(named: "Heroine")
        sound?.play()
    }
}

但是这个声音应用运行时并不会发出。这是因为传统上，这段声音的名字叫“Hero”，大概是出于平权的考虑，苹果将它改名为“Heroine”了。但是程序代码里的，没改，还是叫“Hero”。所以，想在自己的应用里使用它，必须使用

 sound = NSSound(named: "Hero")

这可是连文档里都没有的。只能自己搜索加猜测才能摸索到。

苹果还真是个老六。如果你真想平权，还想保证兼容性。那你让"Hero"和"Heroine"可以同时使用就可以了啊。这么做很难吗？

Best Practice of URL Related Operations with Strings

What is a URL?

A Uniform Resource Locator (URL), colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it.

https://en.wikipedia.org/wiki/URL

URL shown in address bar of a browser

In a browser like Safari or Chrome, a URL is shown in a human friendly way. For example, you may see a URL like this for https://zh.wikipedia.org/wiki/统一资源定位符, this is the Chinese version of URL page on Wikipedia.

https://zh.wikipedia.org/wiki/统一资源定位符

URL dealt by social media

However, the human friendly URLs are not standard and not allowed by social media platforms like Weibo and Twitter. Here are the results that sharing https://zh.wikipedia.org/wiki/统一资源定位符 on the above two platforms.

Weibo
url shared on weibo

Twitter
url shared on twitter

Both of them are not shown the URL correctly, as the Chinese characters are not allowed to be used in a URL directly.

URL with percentage encoding

In fact, those characters are converted by a method called percentage. Here is a percentage url:https://zh.wikipedia.org/wiki/%E7%BB%9F%E4%B8%80%E8%B5%84%E6%BA%90%E5%AE%9A%E4%BD%8D%E7%AC%A6. The percentage URL can be used in social media platforms as well as in browsers.

Detecting URLs from Strings

We use NSDataDetector to get the URLs from a String.

let urlString = "This is a URL: https://zh.wikipedia.org/wiki/统一资源定位符"
let dataDetector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
dataDetector.matches(in: urlString, range: NSRange(location: 0, length: (urlString as NSString).length))
    .forEach {
        print($0.range) // {15, 37}
        print(urlString[Range($0.range, in: urlString)!]) // https://zh.wikipedia.org/wiki/统一资源定位符
        print($0.url!.absoluteString) // https://zh.wikipedia.org/wiki/%E7%BB%9F%E4%B8%80%E8%B5%84%E6%BA%90%E5%AE%9A%E4%BD%8D%E7%AC%A6
}

The benefit of using NSDataDetector is that we could get the percentage URL automatically.

Bugs of NSDataDetector with link type

The above was enough for String and URLs. However, good things do not always happen. In practice, I found that there were some bugs in NSDataDetector which lead something fatal.

let s = """
// no issue
1. iOS版：https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
2. iOS:https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
3. iOS https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

// issue
4. iOS：https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
5. iOS·https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
6. iOSˆhttps://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
7. iOSøhttps://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
8. iOS_https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

// unknown scheme issue
9. iOShttps://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8
"""

let dataDetector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)

dataDetector.matches(in: s, range: NSRange(location: 0, length: (s as NSString).length))
     .enumerated().forEach { index, match in
        print(index + 1)
        print(match.url!.absoluteString)
        print(match.url!.scheme!)
        print(s[Range(match.range, in: s)!])
        print()
}

The result is

1
https://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
https
https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

2
https://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
https
https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

3
https://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
https
https://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

4
http://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
http
itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

5
http://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
http
itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

6
http://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
http
itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

7
http://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
http
itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

8
http://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
http
itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

9
iOShttps://itunes.apple.com/cn/app/%E5%92%95%E5%94%A72/id1366583897?mt=8
iOShttps
iOShttps://itunes.apple.com/cn/app/咕唧2/id1366583897?mt=8

From 4 to 8, the range of match dropped the https:// part from the original string. For the last, the scheme of the URL was not as expected.

Workaround

NSDataDetector is an API provided by Apple. We could file a bug and wait until Apple fixes it. Meanwhile, we should write a workaround and keep our apps working.

For issues in 4 to 8, we should double check if there were missing schemes ahead. If there was, we should recalculate the new NSRange and URL, as the old ones were not accuracy.

For the last issue, we thought it was a typing mistake and we would leave it alone.

import Foundation

extension NSTextCheckingResult {
    // FIXME: - Workaround for Apple API Issue
    public func extendedResultForHttp(of str:String) -> (NSRange, URL)? {
        guard resultType == .link else {
            return nil
        }
        
        guard url?.scheme?.lowercased().hasPrefix("http") ?? false else {
            return nil
        }
        
        // check bug with http:// or https://
        let httpScheme = "http://"
        let httpsScheme = "https://"
        let otherScheme = "x://"
        var location = self.range.location - (httpScheme as NSString).length
        
        if location >= 0 {
            let lowerBound = str.index(str.startIndex, offsetBy: location)
            let upperBound = str.index(lowerBound, offsetBy: httpScheme.count)
            
            if httpScheme == str[lowerBound..<upperBound] {
                let _nsRange = NSRange(location: location, length: (httpScheme as NSString).length + self.range.length)
                let url = URL(string: urlStringWithOriginalScheme(httpScheme)!)!
                
                return (_nsRange, url)
            }
        }
        
        location = self.range.location - (httpsScheme as NSString).length
        
        if location >= 0 {
            let lowerBound = str.index(str.startIndex, offsetBy: location)
            let upperBound = str.index(lowerBound, offsetBy: httpsScheme.count)
            
            if httpsScheme == str[lowerBound..<upperBound] {
                let _nsRange = NSRange(location: location, length: (httpsScheme as NSString).length + self.range.length)
                let url = URL(string: urlStringWithOriginalScheme(httpsScheme)!)!
                
                return (_nsRange, url)
            }
        }
        
        // check bug with other protocols
        location = self.range.location - (otherScheme as NSString).length
        
        if location >= 0 {
            let lowerBound = str.index(str.startIndex, offsetBy: location)
            let upperBound = str.index(lowerBound, offsetBy: httpsScheme.count)
            let schemeStr = String(str[lowerBound..<upperBound])
            let _nsRange = NSRange(location: 0, length: (schemeStr as NSString).length)
            let regularExpress = try! NSRegularExpression(pattern: "^[a-zA-Z]+://", options: .anchorsMatchLines)
            
            if regularExpress.firstMatch(in: schemeStr, range: _nsRange) != nil {
                return nil
            }
        }
        
        // good result
        return (self.range, self.url!)
    }
    
    private func urlStringWithOriginalScheme(_ originalScheme:String) -> String? {
        if let url = self.url, var scheme = url.scheme {
            scheme += "://"
            let str = url.absoluteString
            return originalScheme + String(str[str.index(str.startIndex, offsetBy: scheme.count)...])
        }
        
        return nil
    }
}

Others

Swift 5 String补遗

Weight and Line Height of Font between macOS and iOS

When converting text to image, the converted images were different between macOS and iOS. The main differences are font weight and line height.

Font Weight

Thought the font weight and the fonts are the same, on macOS the font result is always thicker. I don't know why. But in my experience, if you use "HelveticaNeue-Light" for iOS, use "HelveticaNeue-Thin" for macOS.

Line Height

The line height of font is even tricky.

Equation

In Apple's doc, Apple gives below graph. We could draw a simple equation from the graph.

line height = ascent + decent + line gap (leading)

textpg_intro_2x

So I did two tests on both iOS and macOS in Playgound.

// macOS
func getFontInfo(_ name:String) {
    let font = NSFont(name: name, size: 17.0)!
    print(font.ascender) // 13.09033203125
    print(font.descender) // -3.90966796875
    print(font.leading) // 0.0
    print(font.ascender - font.descender + font.leading) // 17.0
    
    let layoutManager = NSLayoutManager()
    print(layoutManager.defaultLineHeight(for: font)) // 20.0
}

getFontInfo("Helvetica")

// iOS
func getFontInfo(_ name:String) {
    let font = UIFont(name: name, size: 17.0)!
    print(font.ascender) // 15.64033203125
    print(font.descender) // -3.90966796875
    print(font.leading) // 0.0
    print(font.ascender - font.descender + font.leading) // 19.55
    print(font.lineHeight) // // 19.55
}

getFontInfo("Helvetica")

From the two tests, we could draw two conclusions:
  1. The equation on iOS was balanced, but on macOS was not.
  2. For the same font with the same weight, the ascender were different.

I didn't know why those happened. So I sent an "Apple Developer Technical Support". Here was the reply from Apple.

apple's reply

According to Apple, if I wanted to use the equation, I should use Core Text framework. But in fact Apple didn't provide line height in Core Text.

Then I did another two tests.

// macOS
func getLineHeightForFontName(_ name:String) {
    let font = CTFontCreateWithName(name as CFString, 17.0, nil)
    
    print(CTFontGetAscent(font)) // 13.09033203125
    print(CTFontGetDescent(font)) // 3.90966796875
    print(CTFontGetLeading(font)) // 0.0
}

getLineHeightForFontName("Helvetica")

// iOS
func getLineHeightForFontName(_ name:String) {
    let font = CTFontCreateWithName(name as CFString, 17.0, nil)
    
    print(CTFontGetAscent(font)) // 13.09033203125
    print(CTFontGetDescent(font)) // 3.90966796875
    print(CTFontGetLeading(font)) // 0.0
}

getLineHeightForFontName("Helvetica")

From all four tests, we could get the conclusions:
  1. Though on iOS, the equation was balanced. The ascent property was modified by Apple.
  2. On macOS, the line height was modified by Apple.
  3. From the above two conclusions, both NSFont and UIFont were not trusted. The only trusted line height was something we get from Core Text.

Line Height

#if os(macOS)
func getLineHeight(_ font:NSFont) -> CGFloat {
    let ctFont = CTFontCreateWithName(font.fontName as CFString, font.pointSize, nil)
    return CTFontGetAscent(ctFont) + CTFontGetDescent(ctFont) + CTFontGetLeading(ctFont)
}
#else
func getLineHeight(_ font:UIFont) -> CGFloat {
    let ctFont = CTFontCreateWithName(font.fontName as CFString, font.pointSize, nil)
    return CTFontGetAscent(ctFont) + CTFontGetDescent(ctFont) + CTFontGetLeading(ctFont)
}
#endif

Others

NSTextView Best Practice

Text Programming Guide for iOS

Cocoa Text Architecture Guide

Core Text - Calculating line heights