Serial Port Code Works on Windows, but Throws Error on Android

Question

Hi
I'm using this code in my .NET MAUI app to list available serial ports:

using System.IO.Ports;

namespace PortMauiApp1
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            ListAvailablePorts();
        }

        private void ListAvailablePorts()
        {
            partsLabel.Text = "";
            string[] ports = SerialPort.GetPortNames();
            foreach (string port in ports)
            {
                partsLabel.Text += port + "\n";  
            }
        }
    }
}

It works fine in Windows, but on Android it throws this error:

System.Reflection.TargetInvocationException: 'Exception has been thrown by the target of an invocation.'

Any idea how to fix this?

Answer 1

Hello,

It works fine in Windows, but on Android it throws this error:

This is because SerialPort.GetPortNames is not support Android platform.

On Android, you need to use UsbManager to get the serial device.

#if ANDROID

            var act = Platform.CurrentActivity;

            UsbManager manager = (UsbManager)act.GetSystemService(Context.UsbService);

            IDictionary<string, UsbDevice> devicesDictionary = manager.DeviceList;

#endif

Please refer to Android.Hardware.Usb Namespace for more details about android native serial APIs.

In addition, Android has a policy that prevents access to serial ports by default. You could refer to SerialPort is not supported on Android ? #86619 for more details in repletion from akoeplinger.

I researched a bit and it looks like while in theory the serial port devices are there on Android there's a SELinux policy which prevents you from accessing them: https://stackoverflow.com/questions/30742524/why-cant-i-open-write-from-a-serial-port-on-android That'd really only leave rooted devices or custom OEM versions of Android, I don't think it makes sense for us to support those. I'll add PNSE and the supported OS attributes.

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If you need to access USB-to-serial devices then this library looks like a good alternative choice since it uses the USB Host APIs from Android instead: https://github.com/anotherlab/UsbSerialForAndroid

Best Regards,

Alec Liu.

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