Swift：调用中缺少参数的参数

Question

Hi I am new to Swift, but I've been working on a project to compile a Flutter app into iOS. Below is the portion of the code in Xcode (version 13) where there are errors.

struct QualifiedCharacteristic: Equatable {
    let id: CharacteristicID
    let serviceID: ServiceID
    let peripheralID: PeripheralID
}


extension QualifiedCharacteristic {
    init(_ characteristic: CBCharacteristic) {
        self.init(
            id: characteristic.uuid,
            serviceID: characteristic.service?.uuid ??,
            peripheralID: characteristic.service?.peripheral
        )
    }
}

1. While initialising the three attributes, the first error says "Missing arguments or parameter 'serviceID' in call" and "Missing arguments or parameter 'serviceID' in call, Insert ',serviceID: <#ServiceID#>". When I click on the "Fix" button behind the second error message, it just add another ",serviceID: ServiceID" behind the id attribute. I was wondering what I did wrong there because there is already a serviceID attribute initialised right after id attribute.

2. The second error is after the comma behind serviceID initialisation. The error message says that "Expected expression after operator".

I appreciate everyone's time who can look into these errors.

Answer 1

If the characteristic doesn't have a service, then your init can fail:

change

init(_ characteristic: CBCharacteristic) {

to be a failable initializer

init?(_ characteristic: CBCharacteristic) {

then guard let the values you need to pass to init

guard let service = characteristic.service else { return nil }

now you have an honest, non-optional service, so you have the values you need to pass those to the other init:

    self.init(
        id: characteristic.uuid,
        serviceID: service.serviceID,
        peripheralID: service.peripheral
    )
}