建置 Unity iOS xcode 專案遇到的錯誤與解決方案 (Linker error)

王思元 6:37 下午 iOS , Unity

建置 xcode 專案丟出的錯誤訊息：Undefined symbols

最近要在 Unity 建置 iOS 專案遇到的錯誤問題，第一次跑整個建置流程，先在 Unity 執行遊戲建置產生 xcode 專案，再開啟 xcode 專案進行 app 打包建置，但卻遇到以下 linker 錯誤：

Undefined symbols for architecture arm64:
  "_OBJC_CLASS_$_MFMailComposeViewController", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_OBJC_CLASS_$_SLComposeViewController", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_SLServiceTypeFacebook", referenced from:
      -[ISN_SocialGate fbPost:url:media:] in ISN_SocialGate.o
  "_ACAccountTypeIdentifierTwitter", referenced from:
      -[ISN_SocialGate twitterPostGif:url:] in ISN_SocialGate.o
      -[IOSTwitterPlugin authificateUser] in ISN_SocialGate.o
      -[IOSTwitterPlugin loadUserData] in ISN_SocialGate.o
      -[IOSTwitterPlugin IsTwitterAuthed] in ISN_SocialGate.o
  "_OBJC_CLASS_$_SLRequest", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_OBJC_CLASS_$_ACAccountStore", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_OBJC_CLASS_$_SLComposeServiceViewController", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_OBJC_CLASS_$_MFMessageComposeViewController", referenced from:
      objc-class-ref in ISN_SocialGate.o
  "_SLServiceTypeTwitter", referenced from:
      -[ISN_SocialGate twitterPost:url:media:] in ISN_SocialGate.o
      ___37-[ISN_SocialGate twitterPostGif:url:]_block_invoke in ISN_SocialGate.o
      ___32-[IOSTwitterPlugin loadUserData]_block_invoke in ISN_SocialGate.o
      -[IOSTwitterPlugin postWithMedia:media:] in ISN_SocialGate.o
      -[IOSTwitterPlugin post:] in ISN_SocialGate.o
      -[IOSTwitterPlugin IsTwitterAvaliable] in ISN_SocialGate.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

原因與解決方案

第一次使用 xcode 來建置，透過 Google 搜尋錯誤訊息了解其問題，是我們專案使用到的第三方函數庫 (third-party library)，Stan’s Assets 中的 Ultimate Mobile，使用到 iOS framework，但在 xcode 專案卻沒有設定引用，所以建置 linker stage 丟出如此錯誤。

解決方案就是修改 xcode project 組態,，加入找不到 Symbols 所屬的 framework 即可：

View > Navigators > Show Project Navigator
在視窗中點選專案圖示，例如這次是 Unity-iPhone
在設定頁中找到 General > Linked Frameworks and Libraries
加入缺少的函數庫
- 應該根據自己專案的 Undefined symbols 訊息，來設定需要額外引用的 frameworks，至於怎麼知道缺少的 Symbols 要引用哪些 frameworks 或是 libraries，Google search 會是一個很好的查詢管道
- GameKit.framework
- Social.framework
- Accounts.framework
- MessageUI.framework
- Twitter.framework