UserControl child fill Window - wpf

Question

I have a UserControl that is a portion of a wpf window.
<Window>
<Grid>
<!--some other display elements would be here-->
<local:MyUserControl x:Name="Foo" Padding="0,42,0,50"/>
</Grid>
</Window>
Inside MyUserControl I have an element that is a gallery that is normally hidden, but when visible, it should fill the entire screen.
<UserControl>
<Grid>
<!--main display elements would be here-->
<Grid Name="Gallery" Visibility="Hidden">
<Rectangle Fill="Black" Opacity="0.75"/>
<TextBlock Name="GalleryLabel" Foreground="White" TextAlignment="Center">Current Image Title</TextBlock>
<Button Name="CloseGallery" Style="{DynamicResource WhiteTextButton}" Margin="0,0,0,0" Height="25" VerticalAlignment="Top" HorizontalAlignment="Right" Width="25" Click="GalleryClose_OnClick">X</Button>
<Image Name="GalleryImage" Margin="25"/>
</Grid>
</Grid>
</UserControl>
How can I set the Gallery to fill the entire Window rather than just the UserControl?
I was able to get it to work by adding Margin="0,-42,0,-50" to Gallery, but I don't like that solution. I would rather do something that doesn't involve hard-coding values in the UserControl so that I would be able to have more flexiblility in using it.
Normally it looks like:
where the green Foo area is MyUserControl, and the rest of the things in the window are other elements.
At certain points, I have a gallery display an image, which should fill the entire screen like:
which should fill the entire screen and have a black opaque overlay, along with an image displayed on top of the overlay.

Answer 1

Remove the Padding...
You can use:
<local:MyUserControl x:Name="Foo" VerticalAlignment="Stretch" HorizontalAligment="Stretch"/>
EDIT
I may admit that I still am not sure what you want. But I made something which does the same as you showed in the pictures. But be aware that this as an opinion based question, and the answer is my opinion, there are a lot of ways to achieve this. And this is only one of them:
MainWindow
<Window x:Class="MyProject.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:myProject="clr-namespace:MyProject"
Title="MainWindow" >
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="50"/>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Border Background="Gainsboro" Grid.Row="0">
<StackPanel Orientation="Horizontal">
<Button Content="Show gallery" Width="100" Margin="10"/>
<Button Content="Do something else" Width="150" Margin="10"/>
</StackPanel>
</Border>
<myProject:SomeOtherStuff Grid.Row="1" />
<Border Grid.Row="2" Background="Gainsboro">
<StackPanel Orientation="Horizontal">
<Label Content="Buttom area, can be used for something else"/>
</StackPanel>
</Border>
<myProject:GalleryUserControl x:Name="GalleryUserControl" Grid.Row="0" Grid.RowSpan="3" Visibility="Hidden"/>
</Grid>
SomeOtherStuff UserControl
<UserControl x:Class="MyProject.SomeOtherStuff"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid Background="Green">
<Label VerticalAlignment="Center" HorizontalAlignment="Center" Content="Foo" FontSize="30" FontFamily="Verdana"/>
</Grid>
Gallery UserControl
<UserControl x:Class="XamDataGrid.GalleryUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Height="500" Width="800">
<Grid Background="#99000000">
<TextBlock Text="Currect image title" Foreground="White" TextAlignment="Center" VerticalAlignment="Top" HorizontalAlignment="Stretch"/>
<Button Name="CloseGallery" Margin="0,0,0,0" Content="X" Height="25" VerticalAlignment="Top" HorizontalAlignment="Right" Width="25" Click="GalleryClose_OnClick"/>
<Image Margin="30"/>
</Grid>

Answer 2

An Adorner will be best for you. As it floats above everything else and remains outside the VisualTree too.
UserControl2
<UserControl2 ...>
<Grid>
<Grid Background="#FF709FA6" Opacity="0.3" Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Window, Mode=FindAncestor}}"
Height="{Binding ActualHeight, RelativeSource={RelativeSource AncestorType=Window, Mode=FindAncestor}}">
</Grid>
<Grid Width="600" Height="700">
<Grid.Background>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FF37DAEA" Offset="0"/>
<GradientStop Color="#FFE84242" Offset="1"/>
</LinearGradientBrush>
</Grid.Background>
<!-- Gallery controls -->
<Button Content="Welcome to Gallery" HorizontalAlignment="Left" IsHitTestVisible="True" Margin="112,126,0,0" VerticalAlignment="Top" Height="68" FontSize="48" Click="Button_Click_1"/>
<TextBlock HorizontalAlignment="Left" Margin="83,42,0,0" TextWrapping="Wrap" Text="UserControl2" VerticalAlignment="Top" Foreground="#FF1B0D0D"/>
</Grid>
</Grid>
</UserControl2>
UserControl1
Code :
public partial class UserControl1 : UserControl
{
public UserControl1()
{
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
// get root Window
DependencyObject current = LogicalTreeHelper.GetParent(this);
while (!(current is Window))
current = LogicalTreeHelper.GetParent(current);
Window root = current as Window;
IEnumerable children = LogicalTreeHelper.GetChildren(root);
Panel p = null;
foreach (var child in children)
{
p = child as Panel; // get first container panel in Window
break;
}
// Create UserControl2 to add to the adorner
UserControl2 ctrlGallery = new UserControl2();
AdornerLayer layer = AdornerLayer.GetAdornerLayer(p);
GalleryAdorner adorner = new GalleryAdorner(p, ctrlGallery);
layer.Add(adorner);
}
}
public class GalleryAdorner : Adorner
{
private Control _child;
VisualCollection collection;
public GalleryAdorner(UIElement elem, Control child)
: base(elem)
{
collection = new VisualCollection(this);
_child = child;
collection.Add(_child);
}
protected override int VisualChildrenCount
{
get
{
return 1;
}
}
protected override Visual GetVisualChild(int index)
{
if (index != 0) throw new ArgumentOutOfRangeException();
return collection[0];
}
protected override Size MeasureOverride(Size constraint)
{
_child.Measure(constraint);
return _child.DesiredSize;
}
protected override Size ArrangeOverride(Size finalSize)
{
_child.Arrange(new Rect(new Point(0, 0), finalSize));
return new Size(_child.ActualWidth, _child.ActualHeight);
}
}