swift - NSLocale 使用方法 swizzling 更改 currentLocale 输出以进行测试

Question

我正在尝试更改设备 currentLocale 输出以执行一些有趣的单元测试，这是我正在使用的代码，但返回的 currentLocale 似乎没有被覆盖。有什么提示吗？

extension NSLocale {
    class func frLocale()->NSLocale{
        return NSLocale(localeIdentifier: "fr_FR")
    }

    class func forceCurrentLocale(){
        let originalSelector = #selector(NSLocale.currentLocale)
        let swizzledSelector = #selector(self.frLocale)

        let originalMethod = class_getClassMethod(self, originalSelector)
        let swizzledMethod = class_getClassMethod(self, swizzledSelector)

        let didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

        if didAddMethod {
            class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod)
        }
    }
}

//编辑

上面的代码不起作用。但是如果我这样写它就可以了:

class func forceCurrentLocale(){
    let originalSelector = #selector(NSLocale.currentLocale)
    let swizzledSelector = #selector(NSLocale.frLocale)

    let originalMethod = class_getClassMethod(self, originalSelector)
    let swizzledMethod = class_getClassMethod(self, swizzledSelector)

    method_exchangeImplementations(originalMethod, swizzledMethod)
}

在这种情况下，class_addMethod 有什么问题？

Answer 1

您的第一个方法对于调配实例方法是正确的，但不适用于类方法。如果我理解正确的话，会发生什么？

let didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

向类添加一个实例方法，并返回true。然后

 class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))

替换失败的实例方法。

如果您查看 Method Swizzling NSHipster 的文章然后你会发现以下评论:

// When swizzling a class method, use the following:
// Class class = object_getClass((id)self);
// ...
// Method originalMethod = class_getClassMethod(class, originalSelector);
// Method swizzledMethod = class_getClassMethod(class, swizzledSelector);

翻译成 Swift 会是

class func forceCurrentLocale(){
    let originalSelector = #selector(NSLocale.currentLocale)
    let swizzledSelector = #selector(self.frLocale)

    let classObject : AnyClass = object_getClass(self)

    let originalMethod = class_getClassMethod(classObject, originalSelector)
    let swizzledMethod = class_getClassMethod(classObject, swizzledSelector)

    let didAddMethod = class_addMethod(classObject, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

    if didAddMethod {
        class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod)
    }
}

然后 swizzling 按预期工作。 (关键点在于class_addMethod() 在类对象上调用，而不是在 self 上调用。)

但实际上我看不出比你的第二种方法有任何优势。didAddMethod 将始终返回 false 因为 frLocale已经定义为 NSLocale 的类方法。