树莓派3，win10 Iot，串口开发，抄例子，串口获取返回老是null，例子却可以，代码一样，上网查询结果如下：

https://stackoverflow.com/questions/34160376/windows-universal-app-serial-ports-wont-open-serialdevice-fromidasync-always-n

So Microsoft do not mention that you need to add something to the app manifest for serial communication nor is there a tick box in the app manifest GUI for serial communication.

The following needs to be added to your app manifest (create the <Capabilities> section if it doesn't exist):

<Capabilities>
  <DeviceCapability Name="serialcommunication">
    <Device Id="any">
      <Function Type="name:serialPort" />
    </Device>
  </DeviceCapability>
</Capabilities>

UPDATE 10/2016

Microsoft have updated their documentation to reflect this requirement.

https://msdn.microsoft.com/en-us/library/windows/apps/windows.devices.serialcommunication.aspx

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