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_posts/zmediumtomarkdown/2024-09-20-9e43897d99fc.md

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+---
+title: "iOS ≥ 18 NSAttributedString attributes Range 合併的一個行為改變"
+author: "ZhgChgLi"
+date: 2024-09-20T13:03:42.359+0000
+last_modified_at: 2024-09-20T13:03:42.359+0000
+categories: "ZRealm Dev."
+tags: ["ios-app-development","nsattributedstring","ios-18","ios","swift"]
+description: "iOS ≥ 18 開始 NSAttributedString attributes Range 合併會參考 Equatable"
+image:
+  path: /assets/9e43897d99fc/1*PJ_qm75Yz_7y0UUBk8X6bg.jpeg
+render_with_liquid: false
+---
+
+### iOS ≥ 18 NSAttributedString attributes Range 合併的一個行為改變
+
+iOS ≥ 18 開始 NSAttributedString attributes Range 合併會參考 Equatable
+
+
+
+![Photo by [C M](https://unsplash.com/@ubahnverleih?utm_content=creditCopyText&utm_medium=referral&utm_source=unsplash){:target="_blank"}](/assets/9e43897d99fc/1*PJ_qm75Yz_7y0UUBk8X6bg.jpeg)
+
+Photo by [C M](https://unsplash.com/@ubahnverleih?utm_content=creditCopyText&utm_medium=referral&utm_source=unsplash){:target="_blank"}
+#### 問題起因
+
+
+[![](https://repository-images.githubusercontent.com/602927147/57ce75c1-8548-449c-b44a-f4b0451ed5ea)](https://github.com/ZhgChgLi/ZMarkupParser){:target="_blank"}
+
+
+iOS 18 2024/9/17 上線後，之前做的開源專案 [ZMarkupParser](https://github.com/ZhgChgLi/ZMarkupParser){:target="_blank"} 就有開發者回報 iOS 18 在解析部分 HTML 時會發生閃退。
+
+看到這個 Issue 有點困惑，因為程式在以前都沒問題，iOS 18 開始才會閃退，不符合常理，應該是 iOS 18 底層 Foundation 有什麼調整導致。
+#### Crash Trace
+
+Trace Code 後定位到閃退問題點是遍歷 `.breaklinePlaceholder` Attributes 並針對 Range 進行刪除操作時會發生閃退:
+```
+mutableAttributedString.enumerateAttribute(.breaklinePlaceholder, in: NSMakeRange(0, NSMakeRange(0, mutableAttributedString.string.utf16.count))) { value, range, _ in
+  // ...if condition...
+  // mutableAttributedString.deleteCharacters(in: preRange)
+  // ...if condition...
+  // mutableAttributedString.deleteCharacters(in: range)
+}
+```
+
+`.breaklinePlaceholder` 是我自行擴充的一個 NSAttributedString\.Key，用來標記 HTML 標籤資訊，優化換行符號使用:
+```swift
+struct BreaklinePlaceholder: OptionSet {
+    let rawValue: Int
+
+    static let tagBoundaryPrefix = BreaklinePlaceholder(rawValue: 1)
+    static let tagBoundarySuffix = BreaklinePlaceholder(rawValue: 2)
+    static let breaklineTag = BreaklinePlaceholder(rawValue: 3)
+}
+
+extension NSAttributedString.Key {
+    static let breaklinePlaceholder: NSAttributedString.Key = .init("breaklinePlaceholder")
+}
+```
+
+
+> **_但核心問題不是這裡_** _，因為在 iOS 17 以前，輸入的 `mutableAttributedString` 在執行以上操作時不會有問題；代表輸入的資料內容在 iOS 18 有所變動。_ 
+
+
+
+
+#### NSAttributedString attributes: \[NSAttributedString\.Key: Any?\]
+
+在深入挖掘問題之前先介紹一下 NSAttributedString attributes 的 **合併機制** 。
+
+NSAttributedString attributes 會 **自動比較 \.key 相同的相鄰 Range Attributes 物件是否相同，相同則合併成同個 Attribute** 例如：
+```swift
+let mutableAttributedString = NSMutableAttributedString(string: "", attributes: nil)
+mutableAttributedString.append(NSAttributedString(string: "<div>", attributes: [.font: UIFont.systemFont(ofSize: 14)]))
+mutableAttributedString.append(NSAttributedString(string: "<div>", attributes: [.font: UIFont.systemFont(ofSize: 14)]))
+mutableAttributedString.append(NSAttributedString(string: "<p>", attributes: [.font: UIFont.systemFont(ofSize: 14)]))
+mutableAttributedString.append(NSAttributedString(string: "Test", attributes: [.font: UIFont.systemFont(ofSize: 12)]))
+```
+
+**最終 Attributes 合併結果：**
+```swift
+<div><div><p>{
+    NSFont = "<UICTFont: 0x101d13400> font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; font-size: 14.00pt";
+}Test{
+    NSFont = "<UICTFont: 0x101d13860> font-family: \".SFUI-Regular\"; font-weight: normal; font-style: normal; font-size: 12.00pt";
+}
+```
+
+在 `enumerateAttribute(.breaklinePlaceholder...)` 時會得到以下結果:
+```swift
+NSRange {0, 13}: <UICTFont: 0x101d13400> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 14.00pt
+NSRange {13, 4}: <UICTFont: 0x101d13860> font-family: ".SFUI-Regular"; font-weight: normal; font-style: normal; font-size: 12.00pt
+```
+#### NSAttributedString attributes 合併 — 底層實踐方式推測
+
+推測底層是使用 `Set<Hashable>` 做為 Attributes 容器，會自動排除相同的 Attriubte 物件。
+
+但是為了使用方便， `NSAttributedString attributes: [NSAttributedString.Key: Any?]` Value 物件是宣告成 `Any?` Type，沒有限制 Hashable。
+
+也因此推測系統在底層會在 Conform `as? Hashable` 然後使用 Set 合併管理物件。
+
+
+> **_這次的 iOS ≥ 18 調整差異推測就是這邊底層的實現問題。_** 
+
+
+
+
+
+以下是以我們自訂的 `.breaklinePlaceholder` Attributes 為例:
+```swift
+struct BreaklinePlaceholder: Equatable {
+    let rawValue: Int
+
+    static let tagBoundaryPrefix = BreaklinePlaceholder(rawValue: 1)
+    static let tagBoundarySuffix = BreaklinePlaceholder(rawValue: 2)
+    static let breaklineTag = BreaklinePlaceholder(rawValue: 3)
+}
+
+extension NSAttributedString.Key {
+    static let breaklinePlaceholder: NSAttributedString.Key = .init("breaklinePlaceholder")
+}
+
+//
+
+let mutableAttributedString = NSMutableAttributedString(string: "", attributes: nil)
+mutableAttributedString.append(NSAttributedString(string: "<div>", attributes: [.breaklinePlaceholder: NSAttributedString.Key.BreaklinePlaceholder.tagBoundaryPrefix]))
+mutableAttributedString.append(NSAttributedString(string: "<div>", attributes: [.breaklinePlaceholder: NSAttributedString.Key.BreaklinePlaceholder.tagBoundaryPrefix]))
+mutableAttributedString.append(NSAttributedString(string: "<p>", attributes: [.breaklinePlaceholder: NSAttributedString.Key.BreaklinePlaceholder.tagBoundaryPrefix]))
+mutableAttributedString.append(NSAttributedString(string: "Test", attributes: nil))
+```
+#### iOS ≤ 17 前會得到以下 **Attributes 合併結果：**
+```bash
+<div>{
+    breaklinePlaceholder = "NSAttributedStringCrash.BreaklinePlaceholder(rawValue: 1)";
+}<div>{
+    breaklinePlaceholder = "NSAttributedStringCrash.BreaklinePlaceholder(rawValue: 1)";
+}<p>{
+    breaklinePlaceholder = "NSAttributedStringCrash.BreaklinePlaceholder(rawValue: 1)";
+}Test{
+}
+```
+#### iOS ≥ 18 會得到以下 Attributes 合併結果：
+```xml
+<div><div><p>{
+    breaklinePlaceholder = "NSAttributedStringCrash.BreaklinePlaceholder(rawValue: 1)";
+}Test{
+}
+```
+
+
+> **_可以看到同樣的程式在不同版本的 iOS 有不同的結果，這最終導致了後續的 `enumerateAttribute(.breaklinePlaceholder..)` 中的處理邏輯不合預期造成閃退。_** 
+
+
+
+
+#### ⭐️ iOS ≥ 18 NSAttributedString attributes: \[NSAttributedString\.Key: Any?\] 會多參考 Equatable ==⭐️
+
+
+![比較 iOS 17/18 有無實現 Equatable/Hashable 的結果](/assets/9e43897d99fc/1*0TKpBawJoLZUbUKwovRUJQ.png)
+
+比較 iOS 17/18 有無實現 Equatable/Hashable 的結果
+
+
+> **_⭐️⭐️ iOS ≥ 18 會多參考 `Equatable` ，iOS ≤ 17 則不會。⭐️⭐️_** 
+
+
+
+
+
+結合前述， `NSAttributedString attributes: [NSAttributedString.Key: Any?]` Value 物件是宣告成 `Any?` Type， **就觀測結果， iOS ≥ 18 會先參考 `Equatable` 判斷是否相同，然後再使用 `Hashable` Set 合併管理物件。**
+### 結論
+
+
+> NSAttributedString attributes: \[NSAttributedString\.Key: Any?\] 在合併 Range Attribute 時，iOS ≥ 18 會多參考 Equatable，這點與以往不同。 
+
+
+
+
+另外在 iOS 18 開始如果只宣告 `Equatable` XCode Console 也會輸出 Warning:
+
+
+> **_Obj\-C \` \-hash\` invoked on a Swift value of type \`BreaklinePlaceholder\` that is Equatable but not Hashable; this can lead to severe performance problems\._** 
+
+
+
+
+
+
+有任何問題及指教歡迎 [與我聯絡](https://www.zhgchg.li/contact){:target="_blank"} 。
+
+
+
+_[Post](https://medium.com/zrealm-ios-dev/ios-18-nsattributedstring-attributes-range-%E5%90%88%E4%BD%B5%E7%9A%84%E4%B8%80%E5%80%8B%E8%A1%8C%E7%82%BA%E6%94%B9%E8%AE%8A-9e43897d99fc){:target="_blank"} converted from Medium by [ZMediumToMarkdown](https://github.com/ZhgChgLi/ZMediumToMarkdown){:target="_blank"}._