当前在不兼容的共享模式下打开了图钉

Question

I am currently using UWP Toolkit to navigate among app pages. There is a page that is being used for initializing and opening RaspberryPi GPIO pins. The following error occurs after navigating away from that page then trying to navigate back to it again.

The process cannot access the file because it is being used by another process .\\r\\n\\r\\nPin ' is currently opened in an incompatible sharing mode. Make sure this pin is not already in use by this application or another application

I can see that the constructor is being called each time the page is visited and hence there is an attempt to open pins that are already opened. What is the best way to overcome this issue?

Answer 1

You may add NavigationCacheMode = NavigationCacheMode.Required; to the ctor of the page so your app will not create a new instance of it when you navigate there.

Answer 2

What I always do is let a class deal with managing pins so that your user code can request pins to act on.

public class IO
{
    private readonly GpioController _gpioController;
    private readonly Dictionary<int, GpioPin> _pins;
    public IO(GpioController gpioController)
    {
        _gpioController = gpioController;
        _pins = new Dictionary<int, GpioPin>();
    }

    public GpioPin OpenPin(int pin, GpioSharingMode mode)
    {
        if (_pins.ContainsKey(pin))
        {
            var gpioPin = _pins[pin];
            if (gpioPin.SharingMode == mode)
            {
                return gpioPin;
            }
            throw new ArgumentException($"Pin '{pin}' is already configured in mode '{gpioPin.SharingMode}'");
        }
        else
        {
            var gpioPin = _gpioController?.OpenPin(pin, mode);
            _pins[pin] = gpioPin;
            return gpioPin;
        }
    }

}

Then my viewmodels simply request a pin as follows

public MainViewModel()
{
    _io = ServiceContainer.Instance.Get<IO>();

    _brakingPin = _io.OpenPin(4, GpioSharingMode.Exclusive);
    _io.SetDriveMode(_brakingPin, GpioPinDriveMode.Output);
    _io.Write(_brakingPin, GpioPinValue.Low);
}