Question

我试图更改设备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，但似乎返回的currentLocale没有被覆盖。任何提示？

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出了什么问题？

Answer 1

你的第一种方法是正确的混合实例方法，但不适用于班级方法。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))

在类中添加实例方法，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。

如果你看一下NSHipster的Method Swizzling文章，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);

转换为Swift，这将是

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)
    }
}

然后如预期般的混合工作。（关键是这一点 class_addMethod()在类对象上调用，而不在self上调用。）

但实际上我没有看到你的第二种方法有任何优势。 didAddMethod将始终返回false，因为frLocale 已被定义为NSLocale的类方法。

NSLocale使用方法调配来更改currentLocale输出以进行测试

1 个答案: