How to make sure a Popup control match its parent Page when the parent is resized? UWP - xaml

Question

I have a Popup which will fill the whole page when opened.
<Grid x:Name="gridRoot" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Button Content="Open" HorizontalAlignment="Center" Click="{x:Bind viewModel.OpenPopup}" />
<Popup x:Name="popupCorrect" VerticalAlignment="Top" IsOpen="{Binding IsOpen}" IsLightDismissEnabled="False">
<Popup.ChildTransitions>
<TransitionCollection>
<PaneThemeTransition Edge="Left" />
</TransitionCollection>
</Popup.ChildTransitions>
<uc:MyPopup Width="{Binding ElementName=gridRoot, Path=ActualWidth}" Height="{Binding ElementName=gridRoot, Path=ActualHeight}"/>
</Popup>
</Grid>
The Popup is a UserControl
<Grid Background="Red">
<Button Content="Close" HorizontalAlignment="Center" Click="{x:Bind viewModel.ClosePopup}" />
</Grid>
The page
When popup is shown
Close the popup, resize the page, then reopen the popup. Notice that it does not match the new size of container page even though its Width and Height is bound to gridRoot . Do I have to manually set a new Width and Height for the popup? Why can't I achieve this with binding? This issue also appears on mobile during 'OrientationChanged'

Answer 1

Based on Decade Moon comment, this is how to resize the popup to match the parent container as its size changed.
Create a dependency property in the code behind
public double PageWidth
{
get { return (double)GetValue(PageWidthProperty); }
set { SetValue(PageWidthProperty, value); }
}
public static readonly DependencyProperty PageWidthProperty =
DependencyProperty.Register("PageWidth", typeof(double), typeof(GamePage), new PropertyMetadata(0d));
public double PageHeight
{
get { return (double)GetValue(PageHeightProperty); }
set { SetValue(PageHeightProperty, value); }
}
public static readonly DependencyProperty PageHeightProperty =
DependencyProperty.Register("PageHeight", typeof(double), typeof(GamePage), new PropertyMetadata(0d));
Update the value on SizeChanged event
private void GamePage_SizeChanged(object sender, SizeChangedEventArgs e)
{
if (e.NewSize.Width > 0d && e.NewSize.Height > 0d)
{
PageWidth = e.NewSize.Width;
PageHeight = e.NewSize.Height;
}
}
Then in XAML, just use x:Bind to bind the popup width and height
<Popup x:Name="popupCorrect" VerticalAlignment="Top" IsOpen="{Binding IsPopupCorrectOpen, Mode=TwoWay}" IsLightDismissEnabled="False">
<Popup.ChildTransitions>
<TransitionCollection>
<PaneThemeTransition Edge="Left" />
</TransitionCollection>
</Popup.ChildTransitions>
<uc:PopupCorrect Width="{x:Bind PageWidth, Mode=TwoWay}" Height="{x:Bind PageHeight, Mode=TwoWay}"/>
</Popup>
Pretty straight forward. Just remember not to use the ActualWidth or ActualHeight properties for binding source as they do not raise the PropertyChanged event.
Although it has an ActualWidthProperty backing field, ActualWidth does not raise property change notifications and it should be thought of as a regular CLR property and not a dependency property.
For purposes of ElementName binding, ActualWidth does not post updates when it changes (due to its asynchronous and run-time calculated nature). Do not attempt to use ActualWidth as a binding source for an ElementName binding. If you have a scenario that requires updates based on ActualWidth, use a SizeChanged handler.

Answer 2

#PutraKg have a great way.
But I have two way to solve it.
The first is set the VerticalAlignment="Center" HorizontalAlignment="Center" that can make the popup in the center.
But I think youare not content to put it in the center.
The great way is use the screen position.
You can get the Grid's screen postion and make it to popup.
In open button
private void Button_OnClick(object sender, RoutedEventArgs e)
{
var grid = (UIElement)popupCorrect.Parent; //get grid
var p = grid.TransformToVisual (Window.Current.Content).TransformPoint(new Point(0, 0)); //get point
popupCorrect.HorizontalOffset = p.X;
popupCorrect.VerticalOffset = p.Y;
popupCorrect.IsOpen = !popupCorrect.IsOpen;
}