Xcode与iOS版本对Objective-C旧项目的影响及版本升级咨询

Hey there, let’s work through your questions about your legacy Objective-C project built with Xcode 7.2 and targeting iOS 9.0— I’ve dealt with plenty of these scenarios, so let’s break it down clearly:

Sticking with Xcode 7.2 and iOS 9.0 comes with several notable limitations:

• Modern Tool & Service Lockout: Xcode 7.2 is over 8 years old now, so it won’t support the latest App Store Connect submission rules. You’ll also struggle with modern CI/CD tools, as most have dropped support for such outdated Xcode versions.
• API Limitations: The iOS 9.0 SDK included with Xcode 7.2 lacks all APIs introduced after iOS 9—like the UIDocumentBrowserViewController you’re needing. Any new features relying on iOS 10+ tech won’t compile or run here.
• Device Compatibility: Newer iOS devices (iPhone 7 and later) may refuse to install or run your app properly, since Apple has tightened compatibility requirements for apps built with old SDKs.
• Unpatched Vulnerabilities: Neither Xcode 7.2 nor iOS 9 receive security updates anymore. Your app could have unaddressed security flaws, and you might run into unexpected bugs when interacting with newer iOS system behaviors that weren’t accounted for in the old SDK.

Absolutely—Apple has never dropped full support for Objective-C, even as Swift grew in popularity. Here’s what you can expect:

• Legacy Feature Compatibility: All core Objective-C functionality (manual reference counting, categories, protocols, etc.) works flawlessly in Xcode 8 and 9. You won’t need to rewrite any existing code just to upgrade your IDE.
• Seamless Project Migration: When you open your Xcode 7.2 project in Xcode 8 or 9, the IDE will walk you through minor, mostly automated updates (like updating the project format or adjusting build settings for newer SDKs). These are quick to handle.
• Mixed Code Flexibility: If you ever want to add Swift code to your project down the line, Xcode 8/9 handle mixed-language projects smoothly—giving you a path to incrementally modernize parts of the app if you want.

You must upgrade both—here’s why:

• UIDocumentBrowserViewController was introduced in iOS 11, so you need to target at least iOS 11 to use it. But to build for iOS 11, you need Xcode 9 or later (Xcode versions are tightly tied to specific iOS SDKs; Xcode 9 includes the iOS 11 SDK).
• If you tried to "upgrade the iOS version" without updating Xcode, you’d still be stuck with the iOS 9.0 SDK in Xcode 7.2. This SDK doesn’t even include the UIDocumentBrowserViewController header files, so your code would fail to compile immediately.
• Upgrading Xcode also gives you access to better debugging tools, performance improvements, and support for newer devices—all of which will make finishing your project much easier.

内容的提问来源于stack exchange，提问作者user9137841