ProgressRing never shows - windows-phone-8.1

Question

I have created a page, in which I have placed inside the Grid the above:
<ProgressRing x:Name="Ring" HorizontalAlignment="Center" VerticalAlignment="Center" IsEnabled="True"/>
But when I do Ring.IsActive = true; in my code nothing happens! Possibly I am missing something very simple here, but I can't find out what it is.
This is my xaml:
<Page
x:Class="Diakopes_v2._0.AddExpense"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Diakopes_v2._0"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d" Background="#FF0277BD">
<Page.BottomAppBar>
<CommandBar>
<AppBarButton Icon="Accept" Label="Accept" Click="Accept_Click"/>
<AppBarButton Icon="Cancel" Label="Cancel" Click="Cancel_Click"/>
</CommandBar>
</Page.BottomAppBar>
<Grid>
<Grid.Background>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FF0277BD" Offset="0"/>
<GradientStop Color="#FFE1F5FE" Offset="1"/>
</LinearGradientBrush>
</Grid.Background>
<TextBlock Text="New Expense" TextAlignment="Center" FontSize="46" FontFamily="/Assets/Fonts/BebasNeue Bold.ttf#Bebas Neue"></TextBlock>
<StackPanel HorizontalAlignment="Left" Height="564" Margin="0,76,0,0" VerticalAlignment="Top" Width="400">
<TextBox x:Name="Name" PlaceholderText="Name"></TextBox>
<TextBox x:Name="Price" InputScope="Number" PlaceholderText="Price"></TextBox>
</StackPanel>
<ProgressRing x:Name="Ring" HorizontalAlignment="Center" VerticalAlignment="Center" IsEnabled="True"/>
</Grid>
</Page>
and this is my .cs method were I want to use the ProgressRing:
private void Accept_Click(object sender, RoutedEventArgs e) {
Ring.IsActive = true;
Name.Text = Name.Text.Trim();
Price.Text = Price.Text.Trim();
DBHelper dbHelper = new DBHelper();
Price.Text = Price.Text.Replace(",", ".");
ExpensesTable NewExpense = new ExpensesTable(Place.Id, Name.Text, Convert.ToSingle(Price.Text));
dbHelper.InsertExpense(NewExpense);
Ring.IsActive = false;
Frame.Navigate(typeof(Expenses), Place.Name);
}

Answer 1

I just created sample with code that you provided with simple modifications:
Turn on:
private void Accept_Click(object sender, RoutedEventArgs e)
{
Ring.IsActive = true;
}
Turn off:
private void Cancel_Click(object sender, RoutedEventArgs e)
{
Ring.IsActive = false;
}
Look at the screenshot from emulator:
Also, to remove black rect, you should change Background property to Transparent
So, I guess your code works so fast that you haven't time to see how works ProgressRing.