UWP Changing gridview element size programmatically - xaml

Question

I'm trying to use XAML binding to affect the gridview datatemplate element size from a slider on my screen.
I have a gridview made of thumbnails images where the elements are defined as following:
<GridView.ItemTemplate >
<DataTemplate >
<StackPanel Orientation="Vertical"
HorizontalAlignment="Center"
VerticalAlignment="Center"
KeyDown="IsitenterThumb"
BorderBrush="LightSeaGreen"
BorderThickness="1"
PointerWheelChanged="ctlThumbnails_PointerWheelChanged">
<Image Source="{Binding thumb}"
x:Name="thumbimg"
Visibility="Visible"
Height="{Binding ItemSize}" Width="{Binding ItemSize, ElementName=page}" Stretch="Uniform"
Tapped="ThumbnailSelected"
DoubleTapped="CloseThumbnails"
/>
<TextBlock Text="{Binding name}" Margin="5,5"
Foreground="White"
Width="{Binding ItemSize}"
/>
</StackPanel>
</DataTemplate>
And I have the following variable defined as follow:
public double ItemSize
{
get => _itemSize;
set
{
if (_itemSize != value)
{
_itemSize = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(ItemSize)));
}
}
}
private double _itemSize;
public event PropertyChangedEventHandler PropertyChanged;
I would have thought that changing the value of ItemSize would have affected the gridview datatemplate. This is taken litterally from the PhotoLab sample.
Instead I get a single huge "thumbimg" per page... Any help would be greatly appreciated!

Answer 1

Ok... I got it finally. I'm not quite sure what I was doing wrong above, but the code below works.
I have put the DataTemplate as part of a Page.Resource, I'm not sure if this is what was causing the binding issue. However the Xaml code looks like this:
<Page.Resources>
<DataTemplate x:Key="ThumbnailsTemplate">
<StackPanel Orientation="Vertical"
HorizontalAlignment="Center"
VerticalAlignment="Center"
KeyDown="IsitenterThumb"
BorderBrush="LightSeaGreen"
BorderThickness="1"
<Image Source="{Binding thumb}"
x:Name="thumbimg"
Visibility="Visible"
Height="{Binding ItemSize, ElementName=page}" Width="{Binding ItemSize, ElementName=page}"
Stretch="Uniform"
Tapped="ThumbnailSelected"
DoubleTapped="CloseThumbnails"
/>
<TextBlock Text="{Binding name}" Margin="5,5"
Foreground="White" Width="{Binding ItemSize}"
/>
</StackPanel>
</DataTemplate>
</Page.Resources>
<GridView x:Name = "ctlThumbnails" Grid.Column="0"
BorderBrush="White" BorderThickness="2"
Grid.RowSpan="4" Grid.Row="0" Grid.ColumnSpan="3" Height ="auto" Width="auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
Margin="30,30,30,30" KeyDown="IsitenterThumb"
DoubleTapped="CloseThumbnails"
ItemTemplate="{StaticResource ThumbnailsTemplate}">
</GridView>
And here is the C# code to affect the bound variable ItemSize
public event PropertyChangedEventHandler PropertyChanged;
public double ItemSize
{
get => _itemSize;
set
{
if (_itemSize != value)
{
_itemSize = value;
topcmdbarcontent.Text = "Thumb Size:" + _itemSize.ToString();
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(ItemSize)));
}
}
}
private double _itemSize;
From this, when you change the value of ItemSize, through a ValueChanged event, for example, it does change the grid element size dynamically.