PassthroughSubject 完成完成未调用

编程问答 2022-05-25

问题描述

我正在尝试使用 Combine 与 CoreBluetooth 通信，但是我的 PassthroughSubject 完成处理程序没有被调用。您可以在下面看到代码的粗略布局。 Detailviewmodel 包含蓝牙外设和要发送的数据。

final class Detailviewmodel: NSObject,ObservableObject,CBPeripheralDelegate {
    // Called when the correct write characteristic is found
    private var writeCharacteristicReceived = PassthroughSubject<CBCharacteristic,Never>()
    // Used to send and listen for peripheral data
    private var bluetoothDidChange = PassthroughSubject<Data,Error>()

    func open() -> AnyPublisher<Data,Error> {
        writeCharacteristicReceived.tryMap { characteristic -> AnyPublisher<Data,Error> in
            print("Write char",characteristic)

            let data: Data = try constructPayload()

            self.peripheral?.writeValue(data,for: characteristic,type: .withoutResponse)

            return self.bluetoothDidChange.erasetoAnyPublisher()
        }
        .switchToLatest()
        .erasetoAnyPublisher()
    }

    func peripheral(_ peripheral: CBPeripheral,didUpdateValueFor characteristic: CBCharacteristic,error: Error?) {
        print("Did update value",characteristic.value ?? Data())
        guard let value = characteristic.value,value.count >= 84 else { return }

        defer {
            // Never called
            bluetoothDidChange.send(completion: .finished)
        }

        do {
            let message: Data = try parse(value)
            bluetoothDidChange.send(message)
            // Never called when placed here either
            // bluetoothDidChange.send(completion: .finished)
        } catch {
            bluetoothDidChange.send(completion: .failure(error))
        }
    }
}

然后我在视图本身中监听这些变化，如下所示

viewmodel.open().sink(receiveCompletion: { (completion) in
    print("Open completion: \(completion)")
},receiveValue: { (payload) in
    print("Open payload \(payload)")
}).store(in: &cancellable)

现在，这适用于不时接收值，并且在发生错误时正确调用完成块。但是我从来没有得到完成的完成处理程序，即使我专门做了 send(completion: .finished)。谁能帮帮我？

解决方法

与从未调用 writeCharacteristicReceived.send(completion: .finished) 相关的问题。将其添加到委托调用的函数中解决了问题。

func peripheral(_ peripheral: CBPeripheral,didDiscoverDescriptorsFor characteristic: CBCharacteristic,error: Error?) {
    if let error = error {
        writeCharacteristicDiscovered.send(completion: .failure(error))
    }
    writeCharacteristicDiscovered.send(characteristic)
    writeCharacteristicDiscovered.send(completion: .finished)
}
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