How to reliably get actual dimensions of a UWP Popup? - windows

Question

I have a UWP App which contains a Page which has 4 Popups defined on it. Each Popup is data-bound to a separate Boolean in the View Model. By manipulating the VM, I can make any of the 4 popus appear - only 1 at a time - maximum.
I would like to control where these Popups appear, so I've added "Opened" event handlers to each of them. The event handlers do the appropriate math to calculate Vertical & HorizontalOffset for the Popups.
This question, which was never answered is my problem as well. To explain it better, querying the popups ActualWidth/Height gives nonsense values. All of my popups are different sizes but all are landscape (width > height). I consistently get ActualWidth=310 & ActualHeight=779 for all of them.
By using the Popup's Child's dimensions (always a Grid) in the math, 2 of the 4 work consistently; the other 2 sometimes work, but usually not. EDIT: They fail because the Grid has no dimensions.
I'm assuming the Opened event is as late as possible to allow all Layout / Measures to occur. Short of hard-coding Heights & Widths on the Popups (one of which will have variable content), I've run out of stuff to try.
There's a lot of code, but they're virtually identical. This is one of the ones that works intermittently ...
<Popup x:Name="LoserTool"
IsOpen="{x:Bind vm.bLoseTool, Mode=OneWay}"
Opened="Popup_Opened"
>
<Grid x:Name="gLoserTool"
Background="{StaticResource TaipanHunter_Primary_Dark}"
BorderBrush="{StaticResource TaipanHunter_Primary_Light}"
BorderThickness="2"
Padding="20"
RowSpacing="10">
<Grid.RowDefinitions>
<RowDefinition Height="1.5*" />
<RowDefinition Height="5*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0.2*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="0.2*" />
</Grid.ColumnDefinitions>
<TextBlock Text="Oh No!"
Grid.Column="1"
Grid.Row="0"
Style="{StaticResource TaipanHunter_Title}"
/>
<TextBlock Text="Your tool broke!"
Grid.Column="1"
Grid.Row="1"
Style="{StaticResource Text_LightText}"
/>
<Button Content="Play Again"
Click="StartNewGame"
Grid.Column="1"
Grid.Row="2"
HorizontalAlignment="Center"
Style="{StaticResource Button_Base}"
/>
</Grid>
</Popup>