MainPage.xaml

<Page
    x:Class="SerialDeviceExample.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:SerialDeviceExample"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Loaded="RefreshList"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <Grid>
        <StackPanel HorizontalAlignment="Center" Margin="0,50,0,0">
            <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                <TextBlock Text="Device LIST:" Margin="0,5,10,0" FontSize="18"/>
                <ComboBox Name="cbListDevices" FontSize="18" Margin="0,0,10,0"/>
                <Button Content="Refresh List" Click="RefreshList" />
            </StackPanel>
            <Button Name="btConfigPort" Content="Configure Port" Click="click_ConfigPort" HorizontalAlignment="Center" Margin="0,10,0,0"/>
            <StackPanel Orientation="Horizontal" VerticalAlignment="Center" Margin="0,10,0,0">
                <TextBox Name="tbSendString" FontSize="18" Width="200" Margin="0,0,10,0"/>
                <Button Name="btSendString" Content="Send String" Click="click_SendString"/>
            </StackPanel>
            <Button Name="btReadSerial" Content="Read Port" Click="click_ReadSerial" HorizontalAlignment="Center" Margin="0,10,0,0"/>
            <TextBlock Name="tbReceivedSerial" Text="" HorizontalAlignment="Center"/>
        </StackPanel>
    </Grid>
</Page>