Question

我正在尝试调用一个名为＆＃39; nextPage＆＃39;在一份警卫声明中，但它是在说＆＃39;（）＆＃39;不能转换为Bool＆＃39;。要调用此函数我需要做什么

@IBAction func nextPressed(_ sender: Any) {
    let geoCoder = CLGeocoder()
    geoCoder.geocodeAddressString(address) { (placemarks, error) in
        guard
            let placemark = placemarks?.first,
            let latVar = placemark.location?.coordinate.latitude,
            let lonVar = placemark.location?.coordinate.longitude,
            nextPage() // Error - '()' is not convertible to 'Bool'
            else {
                print("no location found")
                return
        }
    }
}

Answer 1

guard语句用于检查是否满足特定条件。你不能在这个陈述中放置一个不会返回true或false的函数。

参考： https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html

我相信你想要完成的是

@IBAction func nextPressed(_ sender: Any) {
        let geoCoder = CLGeocoder()
        geoCoder.geocodeAddressString(address) { (placemarks, error) in
            guard
                let placemark = placemarks?.first,
                let latVar = placemark.location?.coordinate.latitude,
                let lonVar = placemark.location?.coordinate.longitude
                else {
                    print("no location found")
                    return
            }

            // will only get executed of all the above conditions are met
            nextPage() // moved outside the guard statement

        }
}

Answer 2

你应该调用返回布尔值的函数，或者不要在guard谓词语句中做这样的事情，因为它不适合调用函数。你应该做点什么

guard variable != nil else {
    //handle nil case
}

// continue work with variable, it is guaranteed that it’s not nil.

（Swift）在守卫声明中调用函数

2 个答案: