How to swizzle NSError init without hitting an infinite loop

Question

How to call the original NSError init method when swizzling?

My current implementation

 extension NSError {

    @objc class func errorSwizzle() {
        guard let instance = class_getInstanceMethod(self, #selector(NSError.init(domain:code:userInfo:))),
            let swizzleInstance = class_getInstanceMethod(self, #selector(NSError.init(swizzleDomain:code:info:))) else { return }
        method_exchangeImplementations(instance, swizzleInstance)
    }

    @objc class func errorUnSwizzle() {
        guard let instance = class_getInstanceMethod(self, #selector(NSError.init(domain:code:userInfo:))),
            let swizzleInstance = class_getInstanceMethod(self, #selector(NSError.init(swizzleDomain:code:info:))) else { return }
        method_exchangeImplementations(swizzleInstance, instance)
    }

    @objc convenience init(swizzleDomain: String, code: Int, info: [String : Any]?) {

        /// infinite loop as it calls the swizzled init again.
        self.init(domain: swizzleDomain, code: code, userInfo: info)

        /// Do something.. 
    }
}

Sulthan · Accepted Answer · 2018-12-31T12:24:01.817

2

You have exchanged the implementations, that means you have to call:

@objc convenience init(swizzleDomain: String, code: Int, info: [String : Any]?) {
    self.init(swizzleDomain: swizzleDomain, code: code, info: info)
}

Because self.init(swizzleDomain:...) will contain the original initializer.

edited Dec 31 '18 at 12:24

answered Dec 31 '18 at 12:17

Sulthan

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Thanks, @Sulthan, just found my issue as well and posted that as an answer – Tal Zion Dec 31 '18 at 12:25

How to swizzle NSError init without hitting an infinite loop

1 Answers1