Swift 5.5 的方法调配

Question

我正在尝试覆盖 NSURL 上的 initWithString 方法，我查看了这些过去的问题/帖子。

• Method swizzling in swift 4
• How to swizzle init in Swift
• https://www.uraimo.com/2015/10/23/effective-method-swizzling-with-swift/

我尝试了以下代码，但无法固定新的 log_initWithString 方法，swiftc 不会标记任何内容，但在运行时我会收到 index/index.swift:20: Fatal error: Unexpectedly found nil while unwrapping an Optional value。

import AppKit
import WebKit

let app = NSApplication.shared

//example: https://github.com/kickstarter/ios-oss/blob/39edeeaefb5cfb26276112e0af5eb6948865cf34/Library/DataSource/UIView-Extensions.swift

private var hasSwizzled = false

extension NSURL {
    public final class func doSwizzle() {
        guard !hasSwizzled else { return }

        hasSwizzled = true
        
        let original = Selector("initWithString:")
        let swizzled = Selector("log_initWithString:")

        let originalMethod = class_getInstanceMethod(NSURL.self, original)!
        let swizzledMethod = class_getInstanceMethod(NSURL.self, swizzled)!

        let didAddMethod = class_addMethod(NSURL.self, original, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

        if didAddMethod {
            class_replaceMethod(NSURL.self, swizzled, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod)
        }
    }
    
    @objc internal func log_initWithString(string URLString: String) {
        NSLog("Hello from initWithString")
        
        return log_initWithString(string: URLString)
    }
}

class AppDelegate: NSObject, NSApplicationDelegate {
    let window = NSWindow.init(contentRect: NSRect(x: 0, y: 0, width: 750, height: 600), styleMask: [
        NSWindow.StyleMask.titled,
        NSWindow.StyleMask.closable,
        NSWindow.StyleMask.resizable,
        NSWindow.StyleMask.miniaturizable
    ], backing: NSWindow.BackingStoreType.buffered, defer: false)
    
    func applicationDidFinishLaunching(_ notification: Notification) {
        NSURL.doSwizzle()
        
        let webview = WKWebView(frame: window.contentView!.frame)
        let request = URLRequest(url: URL(string: "https://google.com")!)

        window.contentView?.addSubview(webview)
        webview.load(request)
        
        window.makeKeyAndOrderFront(nil)
        window.orderFrontRegardless()
        window.center()
    }
}

let delegate = AppDelegate()

app.delegate = delegate

app.run()

Answer 1

那是因为

@objc internal func log_initWithString(string URLString: String)

以log_initWithStringWithString: 而不是log_initWithString: 的身份向Objective-C 公开。

明显的解决方法是：

...
let swizzled = Selector("log_initWithStringWithString:")
...

为了更好地进行编译时检查，您可以使用以下语法：

let original = #selector(NSURL.init(string:))
let swizzled = #selector(NSURL.log_initWithString(string:))

这将编译，但至少还有一件事需要修复 - 混合方法返回值。在您的示例中：

@objc internal func log_initWithString(string URLString: String) {
    NSLog("Hello from initWithString")

    return log_initWithString(string: URLString)
}

什么都不返回，而 NSURL 的 init 应该返回 NSURL，所以解决方法是：

@objc internal func log_initWithString(string URLString: String) -> NSURL {
...