I am using the NumericUpDown control from MahApps, because of its +/- buttons and the ability to set the maximum/minimum allowed value. I now need to somehow limit the number of character, that can be input to the box.
For a standard TextBox this would be done with the MaxLength property, but this property does not exist for the NumericUpDown control.
Am I missing something? Is there some other way to achieve this?
No, there is no such property, but you can easily extend NumericUpDown and add it. BTW, when you focus out, it checks the Maximum allowed value and the input value.
C#
using MahApps.Metro.Controls;
using System.Windows;
using System.Windows.Input;
namespace TestApp.Controls
{
class ExtendedNumericUpDown : NumericUpDown
{
public int MaxLenght
{
get { return (int)GetValue(MaxLenghtProperty); }
set { SetValue(MaxLenghtProperty, value); }
}
public static readonly DependencyProperty MaxLenghtProperty =
DependencyProperty.Register(nameof(MaxLenght), typeof(int), typeof(ExtendedNumericUpDown), new PropertyMetadata(10));
protected override void OnPreviewTextInput(TextCompositionEventArgs e)
{
e.Handled = ((System.Windows.Controls.TextBox)e.OriginalSource).Text.Length >= MaxLenght;
base.OnPreviewTextInput(e);
}
}
}
XAML
<ctrl:ExtendedNumericUpDown Minimum="0" Maximum="100" MaxLenght="3"/>
Building on #Alex's answer, you can take it one step further by creating a behavior. The behavior can be used by many different types of controls and you don't need to subclass NumericUpDown
public class MaxCharactersBehavior : Behavior<UIElement>
{
public int MaxCharacters { get; set; }
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.PreviewTextInput += AssociatedObject_PreviewTextInput;
}
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.PreviewTextInput -= AssociatedObject_PreviewTextInput;
}
private void AssociatedObject_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
e.Handled = ((System.Windows.Controls.TextBox)e.OriginalSource).Text.Length >= MaxCharacters;
}
}
<mah:NumericUpDown Width="150" Maximum="999" Minimum="0">
<i:Interaction.Behaviors>
<behaviors:MaxCharactersBehavior MaxCharacters="3" />
</i:Interaction.Behaviors>
</mah:NumericUpDown>
The NumericUpDown control accepts Maximum and Minimum arguments,
<Controls:NumericUpDown Minimum="0" Maximum="{Binding TotalPages}"/>
If you can't find them, try to update the NuGet package of MahApps.
Is there any feature of the TextBlock that allows scrolling to the end always?
I've seen a number of examples that do this in the code behind,
I want to keep the principle of MVVM and not touch the code behind,
I'm looking for a way to do this in XAML.
Have one?
I am assuming your TextBlock is nested within a ScrollViewer. In this case you are going to have to create an attached property. See this related question:
How to scroll to the bottom of a ScrollViewer automatically with Xaml and binding?
i.e. create an attached property:
public static class Helper
{
public static bool GetAutoScroll(DependencyObject obj)
{
return (bool)obj.GetValue(AutoScrollProperty);
}
public static void SetAutoScroll(DependencyObject obj, bool value)
{
obj.SetValue(AutoScrollProperty, value);
}
public static readonly DependencyProperty AutoScrollProperty =
DependencyProperty.RegisterAttached("AutoScroll", typeof(bool), typeof(Helper), new PropertyMetadata(false, AutoScrollPropertyChanged));
private static void AutoScrollPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var scrollViewer = d as ScrollViewer;
if (scrollViewer != null && (bool)e.NewValue)
{
scrollViewer.ScrollToBottom();
}
}
}
Then bind as follows:
<ScrollViewer local:Helper.AutoScroll="{Binding BooleanViewModelPropertyThatTriggersScroll}" .../>
Hi i am working with WPF and using the MVVM pattern. So my problem is that i am trying to bind the selected text of a RichTextBox to a property in my ViewModel but i can't bind the Selection property.
So how can i do it?
Binding the Selection property of the RichTextBox to a property in my ViewModel is the way that i think is better to apply effects and decorations to the text.
If anyone knows a better way to know in the ViewModel the selected text of the RichTextBox, let me know. I am starting to learn about FlowDocuments and working with the RichTextBox so it's why i am a bit lost.
Thanks in advance!
You could use a Behavior:
public class RichTextSelectionBehavior : Behavior<RichTextBox>
{
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.SelectionChanged += RichTextBoxSelectionChanged;
}
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.SelectionChanged -= RichTextBoxSelectionChanged;
}
void RichTextBoxSelectionChanged(object sender, System.Windows.RoutedEventArgs e)
{
SelectedText = AssociatedObject.Selection.Text;
}
public string SelectedText
{
get { return (string)GetValue(SelectedTextProperty); }
set { SetValue(SelectedTextProperty, value); }
}
public static readonly DependencyProperty SelectedTextProperty =
DependencyProperty.Register(
"SelectedText",
typeof(string),
typeof(RichTextSelectionBehavior),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedTextChanged));
private static void OnSelectedTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var behavior = d as RichTextSelectionBehavior;
if (behavior == null)
return;
behavior.AssociatedObject.Selection.Text = behavior.SelectedText;
}
}
XAML usage:
<RichTextBox>
<i:Interaction.Behaviors>
<local:RichTextSelectionBehavior SelectedText="{Binding SelectedText}" />
</i:Interaction.Behaviors>
</RichTextBox>
(where SelectedText is a string property on your ViewModel)
Is there an easy way in WPF to bind VisualStates to enum values? Kinda like DataStateBehavior, but for an Enum?
The best way is to just go ahead and implement a Behavior that does just that -
public class EnumStateBehavior : Behavior<FrameworkElement>
{
public object EnumProperty
{
get { return (object)GetValue(EnumPropertyProperty); }
set { SetValue(EnumPropertyProperty, value); }
}
// Using a DependencyProperty as the backing store for EnumProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty EnumPropertyProperty =
DependencyProperty.Register("EnumProperty", typeof(object), typeof(EnumStateBehavior), new UIPropertyMetadata(null, EnumPropertyChanged));
static void EnumPropertyChanged(object sender, DependencyPropertyChangedEventArgs e)
{
if (e.NewValue == null) return;
EnumStateBehavior eb = sender as EnumStateBehavior;
VisualStateManager.GoToElementState(eb.AssociatedObject, e.NewValue.ToString(), true);
}
}
The usage is extremely simple - use as follows:
<i:Interaction.Behaviors>
<local:EnumStateBehavior EnumProperty="{Binding MyEnumProperty}" />
</i:Interaction.Behaviors>
You can do it in pure xaml by using a DataTrigger per possible enum value with each trigger calling GoToStateAction with a different state. See the example below. For more details take a look at
Enum driving a Visual State change via the ViewModel.
<i:Interaction.Triggers>
<ei:DataTrigger Binding="{Binding ConfirmedAnswerStatus}" Value="Unanswered">
<ei:GoToStateAction StateName="UnansweredState" UseTransitions="False" />
</ei:DataTrigger>
<ei:DataTrigger Binding="{Binding ConfirmedAnswerStatus}" Value="Correct">
<ei:GoToStateAction StateName="CorrectlyAnsweredState" UseTransitions="True" />
</ei:DataTrigger>
<ei:DataTrigger Binding="{Binding ConfirmedAnswerStatus}" Value="Incorrect">
<ei:GoToStateAction StateName="IncorrectlyAnsweredState" UseTransitions="True" />
</ei:DataTrigger>
</i:Interaction.Triggers>
There is a DataStateSwitchBehavior in SL that could be ported to WPF: Anyone have a DataStateSwitchBehavior for WPF4?
the syntax is pretty straightforward:
<is:DataStateSwitchBehavior Binding="{Binding Orientation}">
<is:DataStateSwitchCase Value="Left" State="LeftState"/>
<is:DataStateSwitchCase Value="Right" State="RightState"/>
<is:DataStateSwitchCase Value="Down" State="DownState"/>
<is:DataStateSwitchCase Value="Up" State="UpState"/>
<is:DataStateSwitchCase/>
I was having issues with the above EnumStateBehavior answer.
The PropertyChanged handler will first trigger when the AssociatedObject is null (since the binding has been set up but the Behavior hasn't been attached yet). Also, even when the behavior is first attached, the target elements of the VisualState animation may not yet exist since the behavior may have been attached before other child visual trees.
The solution was to use the Loaded event on the associated object to ensure the binding's initial state is set.
public class EnumStateBehavior : Behavior<FrameworkElement>
{
public static readonly DependencyProperty BindingProperty =
DependencyProperty.Register(nameof(Binding), typeof(object), typeof(EnumStateBehavior), new UIPropertyMetadata(null, BindingPropertyChanged));
public object Binding
{
get { return (object)GetValue(BindingProperty); }
set { SetValue(BindingProperty, value); }
}
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.Loaded += AssociatedObject_Loaded;
}
protected override void OnDetaching()
{
this.AssociatedObject.Loaded -= AssociatedObject_Loaded;
base.OnDetaching();
}
private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
{
if (Binding != null)
GoToState();
}
private void GoToState()
{
VisualStateManager.GoToElementState(this.AssociatedObject, Binding.ToString(), true);
}
private static void BindingPropertyChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var eb = (EnumStateBehavior)sender;
if (e.NewValue == null || eb.AssociatedObject == null || !eb.AssociatedObject.IsLoaded)
return;
eb.GoToState();
}
}
In a Silverlight 3.0 application I'm attempting to create a rectangle in a canvas and have it stretch the whole width of the canvas. I have attempted to do this by binding to the ActualWidth property of a parent container (seem sample below), however while I don't see any binding errors the value is not being bound. The rectangle is not visible as its width is zero. In addition tried binding to the ActualWidth of the canvas that contains my rectangle but this made no difference.
I did find this bug logged on Microsoft Connect but there were no workarounds listed.
Has anyone been able to solve this issue or can they point to solution?
Edit: The original code sample was not accurate of what I'm trying to achieve, updated for more clarity.
<UserControl>
<Border BorderBrush="White"
BorderThickness="1"
CornerRadius="4"
HorizontalAlignment="Center">
<Grid x:Name="GridContainer">
<Rectangle Fill="Aqua"
Width="150"
Height="400" />
<Canvas>
<Rectangle Width="{Binding Path=ActualWidth, ElementName=GridContainer}"
Height="30"
Fill="Red" />
</Canvas>
<StackPanel>
<!-- other elements here -->
</StackPanel>
</Grid>
</Border>
</UserControl>
What are you trying to do that requires you to databind to the ActualWidth property?
This is a known issue with Silverlight, and there is no simple workaround.
One thing that could be done is to set up the visual tree in such a way that you do not need to actually set the Width of the Rectangle, and just allow it to stretch to the appropriate size. So in the example above, if you remove the Canvas (or change the Canvas to some other Panel) and leave the Rectangle's HorizontalAlignment set to Stretch, it will take up all of the available width (effectively the Width of the Grid).
However, this may not be possible in your particular case, and it may really be necessary to set up the databinding. It has already been established that this is not possible directly, but with the help of a proxy object, we can set up the required binding. Consider this code:
public class ActualSizePropertyProxy : FrameworkElement, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public FrameworkElement Element
{
get { return (FrameworkElement)GetValue(ElementProperty); }
set { SetValue(ElementProperty, value); }
}
public double ActualHeightValue
{
get{ return Element == null? 0: Element.ActualHeight; }
}
public double ActualWidthValue
{
get { return Element == null ? 0 : Element.ActualWidth; }
}
public static readonly DependencyProperty ElementProperty =
DependencyProperty.Register("Element", typeof(FrameworkElement), typeof(ActualSizePropertyProxy),
new PropertyMetadata(null,OnElementPropertyChanged));
private static void OnElementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((ActualSizePropertyProxy)d).OnElementChanged(e);
}
private void OnElementChanged(DependencyPropertyChangedEventArgs e)
{
FrameworkElement oldElement = (FrameworkElement)e.OldValue;
FrameworkElement newElement = (FrameworkElement)e.NewValue;
newElement.SizeChanged += new SizeChangedEventHandler(Element_SizeChanged);
if (oldElement != null)
{
oldElement.SizeChanged -= new SizeChangedEventHandler(Element_SizeChanged);
}
NotifyPropChange();
}
private void Element_SizeChanged(object sender, SizeChangedEventArgs e)
{
NotifyPropChange();
}
private void NotifyPropChange()
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("ActualWidthValue"));
PropertyChanged(this, new PropertyChangedEventArgs("ActualHeightValue"));
}
}
}
We can use this in xaml as follows:
<Grid x:Name="LayoutRoot">
<Grid.Resources>
<c:ActualSizePropertyProxy Element="{Binding ElementName=LayoutRoot}" x:Name="proxy" />
</Grid.Resources>
<TextBlock x:Name="tb1" Text="{Binding ActualWidthValue, ElementName=proxy}" />
</Grid>
So we are Binding TextBlock.Text to the ActualWidthValue on the proxy object. The proxy object in turn provides the ActualWidth of the Element, which is provided by another Binding.
This is not a simple solution to the problem, but it is the best that I can think of for how to databind to ActualWidth.
If you explained your scenario a bit more, it may be possible to come up with a simpler solution. DataBinding may not be required at all; would it be possible to just set the property from code in a SizeChanged event handler?
Using the mechanism of attached properties, properties which represent ActualHeight and ActualWidth and are updated by SizeChanged event can be defined. Its usage will look like the following.
<Grid local:SizeChange.IsEnabled="True" x:Name="grid1">...</Grid>
<TextBlock Text="{Binding ElementName=grid1,
Path=(local:SizeChange.ActualHeight)}"/>
Technical details can be found at the following:
http://darutk-oboegaki.blogspot.com/2011/07/binding-actualheight-and-actualwidth.html
The advantage of this solution compared to others is in that the attached properties defined in the solution (SizeChange.ActualHeight and SizeChange.ActualWidth) can be used for any FrameworkElement without creating any sub class. This solution is reusable and less invasive.
In the event that the link becomes stale, here is the SizeChange Class as shown on the link:
// Declare SizeChange class as a sub class of DependencyObject
// because we need to register attached properties.
public class SizeChange : DependencyObject
{
#region Attached property "IsEnabled"
// The name of IsEnabled property.
public const string IsEnabledPropertyName = "IsEnabled";
// Register an attached property named "IsEnabled".
// Note that OnIsEnabledChanged method is called when
// the value of IsEnabled property is changed.
public static readonly DependencyProperty IsEnabledProperty
= DependencyProperty.RegisterAttached(
IsEnabledPropertyName,
typeof(bool),
typeof(SizeChange),
new PropertyMetadata(false, OnIsEnabledChanged));
// Getter of IsEnabled property. The name of this method
// should not be changed because the dependency system
// uses it.
public static bool GetIsEnabled(DependencyObject obj)
{
return (bool)obj.GetValue(IsEnabledProperty);
}
// Setter of IsEnabled property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetIsEnabled(DependencyObject obj, bool value)
{
obj.SetValue(IsEnabledProperty, value);
}
#endregion
#region Attached property "ActualHeight"
// The name of ActualHeight property.
public const string ActualHeightPropertyName = "ActualHeight";
// Register an attached property named "ActualHeight".
// The value of this property is updated When SizeChanged
// event is raised.
public static readonly DependencyProperty ActualHeightProperty
= DependencyProperty.RegisterAttached(
ActualHeightPropertyName,
typeof(double),
typeof(SizeChange),
null);
// Getter of ActualHeight property. The name of this method
// should not be changed because the dependency system
// uses it.
public static double GetActualHeight(DependencyObject obj)
{
return (double)obj.GetValue(ActualHeightProperty);
}
// Setter of ActualHeight property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetActualHeight(DependencyObject obj, double value)
{
obj.SetValue(ActualHeightProperty, value);
}
#endregion
#region Attached property "ActualWidth"
// The name of ActualWidth property.
public const string ActualWidthPropertyName = "ActualWidth";
// Register an attached property named "ActualWidth".
// The value of this property is updated When SizeChanged
// event is raised.
public static readonly DependencyProperty ActualWidthProperty
= DependencyProperty.RegisterAttached(
ActualWidthPropertyName,
typeof(double),
typeof(SizeChange),
null);
// Getter of ActualWidth property. The name of this method
// should not be changed because the dependency system
// uses it.
public static double GetActualWidth(DependencyObject obj)
{
return (double)obj.GetValue(ActualWidthProperty);
}
// Setter of ActualWidth property. The name of this method
// should not be changed because the dependency system
// uses it.
public static void SetActualWidth(DependencyObject obj, double value)
{
obj.SetValue(ActualWidthProperty, value);
}
#endregion
// This method is called when the value of IsEnabled property
// is changed. If the new value is true, an event handler is
// added to SizeChanged event of the target element.
private static void OnIsEnabledChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
// The given object must be a FrameworkElement instance,
// because we add an event handler to SizeChanged event
// of it.
var element = obj as FrameworkElement;
if (element == null)
{
// The given object is not an instance of FrameworkElement,
// meaning SizeChanged event is not available. So, nothing
// can be done for the object.
return;
}
// If IsEnabled=True
if (args.NewValue != null && (bool)args.NewValue == true)
{
// Attach to the element.
Attach(element);
}
else
{
// Detach from the element.
Detach(element);
}
}
private static void Attach(FrameworkElement element)
{
// Add an event handler to SizeChanged event of the element
// to take action when actual size of the element changes.
element.SizeChanged += HandleSizeChanged;
}
private static void Detach(FrameworkElement element)
{
// Remove the event handler from the element.
element.SizeChanged -= HandleSizeChanged;
}
// An event handler invoked when SizeChanged event is raised.
private static void HandleSizeChanged(object sender, SizeChangedEventArgs args)
{
var element = sender as FrameworkElement;
if (element == null)
{
return;
}
// Get the new actual height and width.
var width = args.NewSize.Width;
var height = args.NewSize.Height;
// Update values of SizeChange.ActualHeight and
// SizeChange.ActualWidth.
SetActualWidth(element, width);
SetActualHeight(element, height);
}
}
My solution is to declare my own DependencyProperty called RealWidth and update its value on the SizeChanged event. You can then bind to RealWidth, which will update, unlike the ActualWidth property.
public MyControl()
{
InitializeComponent();
SizeChanged += HandleSizeChanged;
}
public static DependencyProperty RealWidthProperty =
DependencyProperty.Register("RealWidth", typeof (double),
typeof (MyControl),
new PropertyMetadata(500D));
public double RealWidth
{
get { return (double) GetValue(RealWidthProperty); }
set { SetValue(RealWidthProperty, value); }
}
private void HandleSizeChanged(object sender, SizeChangedEventArgs e)
{
RealWidth = e.NewSize.Width;
}
Why not create a simple panel control that inherits from ContentPresenter and actually can provide the current size.
public class SizeNotifyPanel : ContentPresenter
{
public static DependencyProperty SizeProperty =
DependencyProperty.Register("Size",
typeof (Size),
typeof (SizeNotifyPanel),
null);
public Size Size
{
get { return (Size) GetValue(SizeProperty); }
set { SetValue(SizeProperty, value); }
}
public SizeNotifyPanel()
{
SizeChanged += (s, e) => Size = e.NewSize;
}
}
It should then be used as wrapper for the actual content.
<local:SizeNotifyPanel x:Name="Content">
<TextBlock Text="{Binding Size.Height, ElementName=Content}" />
</local:SizeNotifyPanel>
Worked for me like a charm and looks clean.
Based on #darutk's answer, here's an attached property-based solution which does the job very elegantly.
public static class SizeBindings
{
public static readonly DependencyProperty ActualHeightProperty =
DependencyProperty.RegisterAttached("ActualHeight", typeof (double), typeof (SizeBindings),
new PropertyMetadata(0.0));
public static readonly DependencyProperty ActualWidthProperty =
DependencyProperty.RegisterAttached("ActualWidth", typeof (Double), typeof (SizeBindings),
new PropertyMetadata(0.0));
public static readonly DependencyProperty IsEnabledProperty =
DependencyProperty.RegisterAttached("IsEnabled", typeof (bool), typeof (SizeBindings),
new PropertyMetadata(false, HandlePropertyChanged));
private static void HandlePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var element = d as FrameworkElement;
if (element == null)
{
return;
}
if ((bool) e.NewValue == false)
{
element.SizeChanged -= HandleSizeChanged;
}
else
{
element.SizeChanged += HandleSizeChanged;
}
}
private static void HandleSizeChanged(object sender, SizeChangedEventArgs e)
{
var element = sender as FrameworkElement;
SetActualHeight(element, e.NewSize.Height);
SetActualWidth(element, e.NewSize.Width);
}
public static bool GetIsEnabled(DependencyObject obj)
{
return (bool)obj.GetValue(IsEnabledProperty);
}
public static void SetIsEnabled(DependencyObject obj, bool value)
{
obj.SetValue(IsEnabledProperty, value);
}
public static Double GetActualWidth(DependencyObject obj)
{
return (Double) obj.GetValue(ActualWidthProperty);
}
public static void SetActualWidth(DependencyObject obj, Double value)
{
obj.SetValue(ActualWidthProperty, value);
}
public static double GetActualHeight(DependencyObject obj)
{
return (double)obj.GetValue(ActualHeightProperty);
}
public static void SetActualHeight(DependencyObject obj, double value)
{
obj.SetValue(ActualHeightProperty, value);
}
}
Use it like this:
<Grid>
<Border x:Name="Border" behaviors:SizeBindings.IsEnabled="True"/>
<Border MinWidth="{Binding (behaviors:SizeBindings.ActualWidth), ElementName=Border}"/>
</Grid>
I've tested the updated xaml that you publishing using a TestConverter to see what value gets passed to the width and it is working for me (I am using VS 2010 B2). To use the TestConverter just set a breakpoint in the Convert method.
public class TestConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
}
A value of 150 was passed in and the Rectangle had a width of 150.
Were you expecting something different?
This is an as an aside answer which may help someone for binding to the ActualWidth.
My process didn't need a change event, it needed an end result of a value in its current state. So I created a dependency property called Target on my custom control/process as a FrameworkElement and the consumer xaml would bind to the actual object in question.
When it was time for the calculation the code could pulled the actual object and extracted it's ActualWidth from it.
Dependency Property on Control
public FrameworkElement Target
{
get { return (FrameworkElement)GetValue(TargetProperty);}
set { SetValue(TargetProperty, value);}
}
// Using a DependencyProperty as the backing store for Target.
// This enables animation, styling, binding, general access etc...
public static readonly DependencyProperty TargetProperty =
DependencyProperty.Register("Target", typeof(FrameworkElement),
typeof(ThicknessWrapper),
new PropertyMetadata(null, OnTargetChanged));
XAML on Consumer side showing a binding to a Rectangle
<local:ThicknessWrapper Target="{Binding ElementName=thePanel}"/>
<Rectangle x:Name="thePanel" HorizontalAlignment="Stretch" Height="20" Fill="Blue"/>
Code to Acquire
double width;
if (Target != null)
width = Target.ActualWidth; // Gets the current value.
Based on KeithMahoney's answer, it works fine on my UWP App and solves my problem. However, I cannot see my control in Design time because both the initial values of ActualWidthValue and ActualHeightValue are not provided in Design time. Although it works fine in running time, it is inconvenient for designing the layout of my control. With a little modification, this problem can be solved.
In his c# code for both properties ActualWidthValue and ActualHeightValue, add
set {;}
to let us can provide dummy values from XAML code. Although it is no use for running time, it can be used for design time.
In the declaration of Resources of his XAML code, provide c:ActualSizePropertyProxy suitable values for ActualWidthValue and ActualHeightValue such as
ActualHeightValue="800" ActualWidthValue="400"
Then it will show you a 400x800 control in design time.