UWP: binding via ElementName is not updating ui

Question

I have a simple Page with a TextBlock where I want to display its ActualHeight and ActualWidth.

<Page
    x:Class="HaproPlace2.Views.Calibration.CalibrationView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="1080"
    d:DesignWidth="1920"
    x:Name="Page1">
    <Grid>
        <TextBlock Text="{Binding ElementName=Page1, Path=ActualHeight}" Foreground="LimeGreen" />
    </Grid>
</Page>

When the app starts, it shows the right value, but is not updating when resizing the page/window. Is there something special in uwp to get it automatically updating the ui if bound to a dependencyProperty via ElementName?

Alamakanambra Alamakanambra · Accepted Answer · 2020-07-07T07:53:00

See the note here.

Although it [ActualHeight] has an ActualHeightProperty backing field, ActualHeight does not raise property change notifications and it should be thought of as a regular CLR property and not a dependency property.

So your options are:

Subscribe to SizeChanged of Page and update your Text from there
Create and use attached property (it's basically the same, but hidden in attached prop)

UWP: binding via ElementName is not updating ui

2 Answers