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Get width and height of Grid one way from XAML (target) to source (property) [duplicate]

I want to write a ViewModel that always knows the current state of some read-only dependency properties from the View.
Specifically, my GUI contains a FlowDocumentPageViewer, which displays one page at a time from a FlowDocument. FlowDocumentPageViewer exposes two read-only dependency properties called CanGoToPreviousPage and CanGoToNextPage. I want my ViewModel to always know the values of these two View properties.
I figured I could do this with a OneWayToSource databinding:
<FlowDocumentPageViewer
CanGoToNextPage="{Binding NextPageAvailable, Mode=OneWayToSource}" ...>
If this was allowed, it would be perfect: whenever the FlowDocumentPageViewer's CanGoToNextPage property changed, the new value would get pushed down into the ViewModel's NextPageAvailable property, which is exactly what I want.
Unfortunately, this doesn't compile: I get an error saying 'CanGoToPreviousPage' property is read-only and cannot be set from markup. Apparently read-only properties don't support any kind of databinding, not even databinding that's read-only with respect to that property.
I could make my ViewModel's properties be DependencyProperties, and make a OneWay binding going the other way, but I'm not crazy about the separation-of-concerns violation (ViewModel would need a reference to the View, which MVVM databinding is supposed to avoid).
FlowDocumentPageViewer doesn't expose a CanGoToNextPageChanged event, and I don't know of any good way to get change notifications from a DependencyProperty, short of creating another DependencyProperty to bind it to, which seems like overkill here.
How can I keep my ViewModel informed of changes to the view's read-only properties?

Yes, I've done this in the past with the ActualWidth and ActualHeight properties, both of which are read-only. I created an attached behavior that has ObservedWidth and ObservedHeight attached properties. It also has an Observe property that is used to do the initial hook-up. Usage looks like this:
<UserControl ...
SizeObserver.Observe="True"
SizeObserver.ObservedWidth="{Binding Width, Mode=OneWayToSource}"
SizeObserver.ObservedHeight="{Binding Height, Mode=OneWayToSource}"
So the view model has Width and Height properties that are always in sync with the ObservedWidth and ObservedHeight attached properties. The Observe property simply attaches to the SizeChanged event of the FrameworkElement. In the handle, it updates its ObservedWidth and ObservedHeight properties. Ergo, the Width and Height of the view model is always in sync with the ActualWidth and ActualHeight of the UserControl.
Perhaps not the perfect solution (I agree - read-only DPs should support OneWayToSource bindings), but it works and it upholds the MVVM pattern. Obviously, the ObservedWidth and ObservedHeight DPs are not read-only.
UPDATE: here's code that implements the functionality described above:
public static class SizeObserver
{
public static readonly DependencyProperty ObserveProperty = DependencyProperty.RegisterAttached(
"Observe",
typeof(bool),
typeof(SizeObserver),
new FrameworkPropertyMetadata(OnObserveChanged));
public static readonly DependencyProperty ObservedWidthProperty = DependencyProperty.RegisterAttached(
"ObservedWidth",
typeof(double),
typeof(SizeObserver));
public static readonly DependencyProperty ObservedHeightProperty = DependencyProperty.RegisterAttached(
"ObservedHeight",
typeof(double),
typeof(SizeObserver));
public static bool GetObserve(FrameworkElement frameworkElement)
{
frameworkElement.AssertNotNull("frameworkElement");
return (bool)frameworkElement.GetValue(ObserveProperty);
}
public static void SetObserve(FrameworkElement frameworkElement, bool observe)
{
frameworkElement.AssertNotNull("frameworkElement");
frameworkElement.SetValue(ObserveProperty, observe);
}
public static double GetObservedWidth(FrameworkElement frameworkElement)
{
frameworkElement.AssertNotNull("frameworkElement");
return (double)frameworkElement.GetValue(ObservedWidthProperty);
}
public static void SetObservedWidth(FrameworkElement frameworkElement, double observedWidth)
{
frameworkElement.AssertNotNull("frameworkElement");
frameworkElement.SetValue(ObservedWidthProperty, observedWidth);
}
public static double GetObservedHeight(FrameworkElement frameworkElement)
{
frameworkElement.AssertNotNull("frameworkElement");
return (double)frameworkElement.GetValue(ObservedHeightProperty);
}
public static void SetObservedHeight(FrameworkElement frameworkElement, double observedHeight)
{
frameworkElement.AssertNotNull("frameworkElement");
frameworkElement.SetValue(ObservedHeightProperty, observedHeight);
}
private static void OnObserveChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
{
var frameworkElement = (FrameworkElement)dependencyObject;
if ((bool)e.NewValue)
{
frameworkElement.SizeChanged += OnFrameworkElementSizeChanged;
UpdateObservedSizesForFrameworkElement(frameworkElement);
}
else
{
frameworkElement.SizeChanged -= OnFrameworkElementSizeChanged;
}
}
private static void OnFrameworkElementSizeChanged(object sender, SizeChangedEventArgs e)
{
UpdateObservedSizesForFrameworkElement((FrameworkElement)sender);
}
private static void UpdateObservedSizesForFrameworkElement(FrameworkElement frameworkElement)
{
// WPF 4.0 onwards
frameworkElement.SetCurrentValue(ObservedWidthProperty, frameworkElement.ActualWidth);
frameworkElement.SetCurrentValue(ObservedHeightProperty, frameworkElement.ActualHeight);
// WPF 3.5 and prior
////SetObservedWidth(frameworkElement, frameworkElement.ActualWidth);
////SetObservedHeight(frameworkElement, frameworkElement.ActualHeight);
}
}

I use a universal solution which works not only with ActualWidth and ActualHeight, but also with any data you can bind to at least in reading mode.
The markup looks like this, provided ViewportWidth and ViewportHeight are properties of the view model
<Canvas>
<u:DataPiping.DataPipes>
<u:DataPipeCollection>
<u:DataPipe Source="{Binding RelativeSource={RelativeSource AncestorType={x:Type Canvas}}, Path=ActualWidth}"
Target="{Binding Path=ViewportWidth, Mode=OneWayToSource}"/>
<u:DataPipe Source="{Binding RelativeSource={RelativeSource AncestorType={x:Type Canvas}}, Path=ActualHeight}"
Target="{Binding Path=ViewportHeight, Mode=OneWayToSource}"/>
</u:DataPipeCollection>
</u:DataPiping.DataPipes>
<Canvas>
Here is the source code for the custom elements
public class DataPiping
{
#region DataPipes (Attached DependencyProperty)
public static readonly DependencyProperty DataPipesProperty =
DependencyProperty.RegisterAttached("DataPipes",
typeof(DataPipeCollection),
typeof(DataPiping),
new UIPropertyMetadata(null));
public static void SetDataPipes(DependencyObject o, DataPipeCollection value)
{
o.SetValue(DataPipesProperty, value);
}
public static DataPipeCollection GetDataPipes(DependencyObject o)
{
return (DataPipeCollection)o.GetValue(DataPipesProperty);
}
#endregion
}
public class DataPipeCollection : FreezableCollection<DataPipe>
{
}
public class DataPipe : Freezable
{
#region Source (DependencyProperty)
public object Source
{
get { return (object)GetValue(SourceProperty); }
set { SetValue(SourceProperty, value); }
}
public static readonly DependencyProperty SourceProperty =
DependencyProperty.Register("Source", typeof(object), typeof(DataPipe),
new FrameworkPropertyMetadata(null, new PropertyChangedCallback(OnSourceChanged)));
private static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((DataPipe)d).OnSourceChanged(e);
}
protected virtual void OnSourceChanged(DependencyPropertyChangedEventArgs e)
{
Target = e.NewValue;
}
#endregion
#region Target (DependencyProperty)
public object Target
{
get { return (object)GetValue(TargetProperty); }
set { SetValue(TargetProperty, value); }
}
public static readonly DependencyProperty TargetProperty =
DependencyProperty.Register("Target", typeof(object), typeof(DataPipe),
new FrameworkPropertyMetadata(null));
#endregion
protected override Freezable CreateInstanceCore()
{
return new DataPipe();
}
}

If anyone else is interested, I coded up an approximation of Kent's solution here:
class SizeObserver
{
#region " Observe "
public static bool GetObserve(FrameworkElement elem)
{
return (bool)elem.GetValue(ObserveProperty);
}
public static void SetObserve(
FrameworkElement elem, bool value)
{
elem.SetValue(ObserveProperty, value);
}
public static readonly DependencyProperty ObserveProperty =
DependencyProperty.RegisterAttached("Observe", typeof(bool), typeof(SizeObserver),
new UIPropertyMetadata(false, OnObserveChanged));
static void OnObserveChanged(
DependencyObject depObj, DependencyPropertyChangedEventArgs e)
{
FrameworkElement elem = depObj as FrameworkElement;
if (elem == null)
return;
if (e.NewValue is bool == false)
return;
if ((bool)e.NewValue)
elem.SizeChanged += OnSizeChanged;
else
elem.SizeChanged -= OnSizeChanged;
}
static void OnSizeChanged(object sender, RoutedEventArgs e)
{
if (!Object.ReferenceEquals(sender, e.OriginalSource))
return;
FrameworkElement elem = e.OriginalSource as FrameworkElement;
if (elem != null)
{
SetObservedWidth(elem, elem.ActualWidth);
SetObservedHeight(elem, elem.ActualHeight);
}
}
#endregion
#region " ObservedWidth "
public static double GetObservedWidth(DependencyObject obj)
{
return (double)obj.GetValue(ObservedWidthProperty);
}
public static void SetObservedWidth(DependencyObject obj, double value)
{
obj.SetValue(ObservedWidthProperty, value);
}
// Using a DependencyProperty as the backing store for ObservedWidth. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ObservedWidthProperty =
DependencyProperty.RegisterAttached("ObservedWidth", typeof(double), typeof(SizeObserver), new UIPropertyMetadata(0.0));
#endregion
#region " ObservedHeight "
public static double GetObservedHeight(DependencyObject obj)
{
return (double)obj.GetValue(ObservedHeightProperty);
}
public static void SetObservedHeight(DependencyObject obj, double value)
{
obj.SetValue(ObservedHeightProperty, value);
}
// Using a DependencyProperty as the backing store for ObservedHeight. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ObservedHeightProperty =
DependencyProperty.RegisterAttached("ObservedHeight", typeof(double), typeof(SizeObserver), new UIPropertyMetadata(0.0));
#endregion
}
Feel free to use it in your apps. It works well. (Thanks Kent!)

Here is another solution to this "bug" which I blogged about here:
OneWayToSource Binding for ReadOnly Dependency Property
It works by using two Dependency Properties, Listener and Mirror. Listener is bound OneWay to the TargetProperty and in the PropertyChangedCallback it updates the Mirror property which is bound OneWayToSource to whatever was specified in the Binding. I call it PushBinding and it can be set on any read-only Dependency Property like this
<TextBlock Name="myTextBlock"
Background="LightBlue">
<pb:PushBindingManager.PushBindings>
<pb:PushBinding TargetProperty="ActualHeight" Path="Height"/>
<pb:PushBinding TargetProperty="ActualWidth" Path="Width"/>
</pb:PushBindingManager.PushBindings>
</TextBlock>
Download Demo Project Here.
It contains source code and short sample usage.
One last note, since .NET 4.0 we are even further away from built-in-support for this, since a OneWayToSource Binding reads the value back from the Source after it has updated it

I like Dmitry Tashkinov's solution!
However it crashed my VS in design mode. That's why I added a line to OnSourceChanged method:
private static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (!((bool)DesignerProperties.IsInDesignModeProperty.GetMetadata(typeof(DependencyObject)).DefaultValue))
((DataPipe)d).OnSourceChanged(e);
}

I think it can be done a bit simpler:
xaml:
behavior:ReadOnlyPropertyToModelBindingBehavior.ReadOnlyDependencyProperty="{Binding ActualWidth, RelativeSource={RelativeSource Self}}"
behavior:ReadOnlyPropertyToModelBindingBehavior.ModelProperty="{Binding MyViewModelProperty}"
cs:
public class ReadOnlyPropertyToModelBindingBehavior
{
public static readonly DependencyProperty ReadOnlyDependencyPropertyProperty = DependencyProperty.RegisterAttached(
"ReadOnlyDependencyProperty",
typeof(object),
typeof(ReadOnlyPropertyToModelBindingBehavior),
new PropertyMetadata(OnReadOnlyDependencyPropertyPropertyChanged));
public static void SetReadOnlyDependencyProperty(DependencyObject element, object value)
{
element.SetValue(ReadOnlyDependencyPropertyProperty, value);
}
public static object GetReadOnlyDependencyProperty(DependencyObject element)
{
return element.GetValue(ReadOnlyDependencyPropertyProperty);
}
private static void OnReadOnlyDependencyPropertyPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
SetModelProperty(obj, e.NewValue);
}
public static readonly DependencyProperty ModelPropertyProperty = DependencyProperty.RegisterAttached(
"ModelProperty",
typeof(object),
typeof(ReadOnlyPropertyToModelBindingBehavior),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
public static void SetModelProperty(DependencyObject element, object value)
{
element.SetValue(ModelPropertyProperty, value);
}
public static object GetModelProperty(DependencyObject element)
{
return element.GetValue(ModelPropertyProperty);
}
}

WPF – Change Property Value in Setter of Another Property

In the following example of my custom control, why I can't change a TransparentColor property in a setter of a SelectedColor property? A solution with callback method works fine, what's the difference between them in the case of change another property?
public class MyColorPicker : Control
{
static MyColorPicker()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(MyColorPicker), new FrameworkPropertyMetadata(typeof(MyColorPicker)));
}
public static readonly DependencyProperty SelectedColorProperty =
DependencyProperty.Register("SelectedColor", typeof(Color), typeof(MyColorPicker), new PropertyMetadata(Color.FromRgb(0, 201, 201), OnSelectedColorChange));
private static void OnSelectedColorChange(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
var colorPicker = (MyColorPicker)sender;
var selectedColor = colorPicker.SelectedColor;
colorPicker.TransparentColor = Color.FromArgb(0, selectedColor.R, selectedColor.G, selectedColor.B);
}
public Color SelectedColor
{
get { return (Color)GetValue(SelectedColorProperty); }
set
{
// Why this not working? BorderStopColor = Color.FromArgb(0, value.R, value.G, value.B);
SetValue(SelectedColorProperty, value);
}
}
private static readonly DependencyPropertyKey TransparentColorPropertyKey =
DependencyProperty.RegisterReadOnly("TransparentColor", typeof(Color), typeof(MyColorPicker), new PropertyMetadata(Color.FromArgb(0, 0, 201, 201)));
public static readonly DependencyProperty TransparentColorProperty = TransparentColorPropertyKey.DependencyProperty;
public Color TransparentColor
{
get { return (Color)GetValue(TransparentColorProperty); }
protected set { SetValue(TransparentColorPropertyKey, value); }
}
}

The setter of a CLR wrapper for a dependency property should only call the SetValue method to set the actual value of the dependency property.
Any other logic should be implemented in the callback.
Also note that the CLR property wrappers are bypassed at runtime when setting dependency properties in XAML (but the callbacks are not):
Why are .NET property wrappers bypassed at runtime when setting dependency properties in XAML?

Callback not working the second time

I am facing an issue with my code below where the call back is getting called only the first time DocText is set. Subsequently setting the DocText is not calling my callback. I am trying to reset the html of the browser by setting the same string to the DocText property.
WebBrowser class
public static readonly DependencyProperty DocumentTextProperty =
DependencyProperty.Register("DocumentText", typeof(string),
typeof(WebBrowser), new
FrameworkPropertyMetadata(string.Empty,TextChangedCallback));
private static void TextChangedCallback(DependencyObject
dependencyObject, DependencyPropertyChangedEventArgs
dependencyPropertyChangedEventArgs)
{
var control = (WebBrowser)dependencyObject;
control._browser.DocumentText = dependencyPropertyChangedEventArgs.NewValue.ToString();
}
public string DocumentText
{
get { return (string)GetValue(DocumentTextProperty); }
set { SetValue(DocumentTextProperty, value); }
}
Factory class that creates the instance of the web browser is using the browsers set binding to bind the dependency property to "DocText"
if (!String.IsNullOrEmpty(documentTextProperty))
{
browser.SetBinding(WebBrowser.DocumentTextProperty, documentTextProperty);
}
And the documentTextProperyt is being set like this from the ViewModel class
DocText = "some html string";
public string DocText
{
get
{
_docText = if(html != null? html: string.empty);
return _docText;
}
set
{
docText = value;
OnPropertyChanged(() = DocText);
}
}

Looks like the Notification is not going back to control(WebBrowser). Please check whether INotifyPropertyChanged is properly implemented. I checked equivalent code in my system and it is properly working.
public class MaskedTextBox : TextBox
{
public static readonly DependencyProperty DocumentTextProperty =
DependencyProperty.Register("DocumentText", typeof(string),
typeof(MaskedTextBox), new PropertyMetadata(default(string), TextChangedCallback));
private static void TextChangedCallback(DependencyObject
dependencyObject, DependencyPropertyChangedEventArgs
dependencyPropertyChangedEventArgs)
{
var control = (MaskedTextBox)dependencyObject;
control.Text= dependencyPropertyChangedEventArgs.NewValue.ToString();
}
public string DocumentText
{
get { return (string)GetValue(DocumentTextProperty); }
set { SetValue(DocumentTextProperty, value); }
}
}
<StackPanel Margin="50,5,5,50">
<local:MaskedTextBox x:Name="text1" DocumentText="{Binding ElementName=text2, Path=Text, Mode=OneWay}"/>
<TextBox x:Name="text2"/>
</StackPanel>
Here if you edit second text box it is updating first one by calling the callback method properly!

Binding Failure in WPF using MVVM

I have created a custom TextEditor control that inherits from AvalonEdit. I have done this to facilitate the use of MVVM and Caliburn Micro using this editor control. The [cut down for display purposes] MvvTextEditor class is
public class MvvmTextEditor : TextEditor, INotifyPropertyChanged
{
public MvvmTextEditor()
{
TextArea.SelectionChanged += TextArea_SelectionChanged;
}
void TextArea_SelectionChanged(object sender, EventArgs e)
{
this.SelectionStart = SelectionStart;
this.SelectionLength = SelectionLength;
}
public static readonly DependencyProperty SelectionLengthProperty =
DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor),
new PropertyMetadata((obj, args) =>
{
MvvmTextEditor target = (MvvmTextEditor)obj;
target.SelectionLength = (int)args.NewValue;
}));
public new int SelectionLength
{
get { return base.SelectionLength; }
set { SetValue(SelectionLengthProperty, value); }
}
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged([CallerMemberName] string caller = null)
{
var handler = PropertyChanged;
if (handler != null)
PropertyChanged(this, new PropertyChangedEventArgs(caller));
}
}
Now, in the view that holds this control, I have the following XAML:
<Controls:MvvmTextEditor
Caliburn:Message.Attach="[Event TextChanged] = [Action DocumentChanged()]"
TextLocation="{Binding TextLocation, Mode=TwoWay}"
SyntaxHighlighting="{Binding HighlightingDefinition}"
SelectionLength="{Binding SelectionLength,
Mode=TwoWay,
NotifyOnSourceUpdated=True,
NotifyOnTargetUpdated=True}"
Document="{Binding Document, Mode=TwoWay}"/>
My issue is SelectionLength (and SelectionStart but let us just consider the length for now as the problem is the same). If I selected something with the mouse, the binding from the View to my View Model works great. Now, I have written a find and replace utility and I want to set the SelectionLength (which has get and set available in the TextEditor control) from the code behind. In my View Model I am simply setting SelectionLength = 50, I implement this in the View Model like
private int selectionLength;
public int SelectionLength
{
get { return selectionLength; }
set
{
if (selectionLength == value)
return;
selectionLength = value;
Console.WriteLine(String.Format("Selection Length = {0}", selectionLength));
NotifyOfPropertyChange(() => SelectionLength);
}
}
when I set SelectionLength = 50, the DependencyProperty SelectionLengthProperty does not get updated in the MvvmTextEditor class, it is like the TwoWay binding to my control is failing but using Snoop there is no sign of this. I thought this would just work via the binding, but this does not seem to be the case.
Is there something simple I am missing, or will I have to set up and event handler in the MvvmTextEditor class which listens for changes in my View Model and updated the DP itself [which presents it's own problems]?
Thanks for your time.

This is because the Getter and Setter from a DependencyProperty is only a .NET Wrapper. The Framework will use the GetValue and SetValue itself.
What you can try is to access the PropertyChangedCallback from your DependencyProperty and there set the correct Value.
public int SelectionLength
{
get { return (int)GetValue(SelectionLengthProperty); }
set { SetValue(SelectionLengthProperty, value); }
}
// Using a DependencyProperty as the backing store for SelectionLength. This enables animation, styling, binding, etc...
public static readonly DependencyProperty SelectionLengthProperty =
DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor), new PropertyMetadata(0,SelectionLengthPropertyChanged));
private static void SelectionLengthPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var textEditor = obj as MvvmTextEditor;
textEditor.SelectionLength = e.NewValue;
}

Here is another answer if you are still open. Since SelectionLength is already defined as a dependency property on the base class, rather than create a derived class (or add an already existing property to the derived class), I would use an attached property to achieve the same functionality.
The key is to use System.ComponentModel.DependencyPropertyDescriptor to subscribe to the change event of the already existing SelectionLength dependency property and then take your desired action in the event handler.
Sample code below:
public class SomeBehavior
{
public static readonly DependencyProperty IsEnabledProperty
= DependencyProperty.RegisterAttached("IsEnabled",
typeof(bool), typeof(SomeBehavior), new PropertyMetadata(OnIsEnabledChanged));
public static void SetIsEnabled(DependencyObject dpo, bool value)
{
dpo.SetValue(IsEnabledProperty, value);
}
public static bool GetIsEnabled(DependencyObject dpo)
{
return (bool)dpo.GetValue(IsEnabledProperty);
}
private static void OnIsEnabledChanged(DependencyObject dpo, DependencyPropertyChangedEventArgs args)
{
var editor = dpo as TextEditor;
if (editor == null)
return;
var dpDescriptor = System.ComponentModel.DependencyPropertyDescriptor.FromProperty(TextEditor.SelectionLengthProperty,editor.GetType());
dpDescriptor.AddValueChanged(editor, OnSelectionLengthChanged);
}
private static void OnSelectionLengthChanged(object sender, EventArgs e)
{
var editor = (TextEditor)sender;
editor.Select(editor.SelectionStart, editor.SelectionLength);
}
}
Xaml below:
<Controls:TextEditor Behaviors:SomeBehavior.IsEnabled="True">
</Controls:TextEditor>

This is how I did this...
public static readonly DependencyProperty SelectionLengthProperty =
DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor),
new PropertyMetadata((obj, args) =>
{
MvvmTextEditor target = (MvvmTextEditor)obj;
if (target.SelectionLength != (int)args.NewValue)
{
target.SelectionLength = (int)args.NewValue;
target.Select(target.SelectionStart, (int)args.NewValue);
}
}));
public new int SelectionLength
{
get { return base.SelectionLength; }
//get { return (int)GetValue(SelectionLengthProperty); }
set { SetValue(SelectionLengthProperty, value); }
}
Sorry for any time wasted. I hope this helps someone else...

Using Dependency Properties With Multiple Instances

I basically have the same problem as this guy here: Error: " 'Subjects' property was already registered by 'Period' " is raised when more than one control is placed on the form
The main difference between us is that I want to subscribe to an event that has access to the local instance when the xaml changes the property.
So I have my UserControl:
public partial class BoardSquare : UserControl
{
public BoardSquare()
{
InitializeComponent();
Location = new BoardLocation(Int32.MinValue, Int32.MinValue);
XPositionProperty =
DependencyProperty.Register("XPosition", typeof(int),
typeof(BoardSquare), new PropertyMetadata(
new PropertyChangedCallback((value, args) =>
{
Location.X = (int)args.NewValue;
resetBackgroundColorToPosition();
})));
YPositionProperty=
DependencyProperty.Register("YPosition", typeof(int),
typeof(BoardSquare), new PropertyMetadata(
new PropertyChangedCallback((value, args)=>
{
Location.Y = (int)args.NewValue;
resetBackgroundColorToPosition();
})));
}
private void resetBackgroundColorToPosition()
{
this.Background = (Brush)(new ColorEnumToBrushesConverter()).Convert(Location.GetSquareColor(), typeof(BlackWhiteColor), null, null);
}
public readonly DependencyProperty XPositionProperty;
public readonly DependencyProperty YPositionProperty;
public int XPosition
{
get
{
return (int)GetValue(XPositionProperty);
}
set
{
SetValue(XPositionProperty, value);
}
}
public int YPosition
{
get
{
return (int)GetValue(YPositionProperty);
}
set
{
SetValue(YPositionProperty, value);
}
}
public BoardLocation Location { get; set; }
}
Here is my XAML:
<local:BoardSquare Grid.Column="3" Grid.Row="0" XPosition="3" YPosition="0"/>
<local:BoardSquare Grid.Column="4" Grid.Row="0" XPosition="4" YPosition="0"/>
From what I understand, the solution is to make XPositionProperty static and then register it in a static constructor. My problem then is I can't access the local instance of the class when my PropertyChangeCallback event happens.
How can I set the property in the XAML and still get an on property changed event in the C# code?
Is there a better solution than dependency properties?
Below is the working code of BoardSquare after I implemented the answer.
public partial class BoardSquare : UserControl
{
static BoardSquare()
{
XPositionProperty =
DependencyProperty.Register("XPosition", typeof(int),
typeof(BoardSquare), new PropertyMetadata(
new PropertyChangedCallback((objectInstance, args) =>
{
BoardSquare boardSquare = (BoardSquare)objectInstance;
boardSquare.Location.X = (int)args.NewValue;
boardSquare.resetBackgroundColorToPosition();
})));
YPositionProperty =
DependencyProperty.Register("YPosition", typeof(int),
typeof(BoardSquare), new PropertyMetadata(
new PropertyChangedCallback((objectInstance, args) =>
{
BoardSquare boardSquare = (BoardSquare)objectInstance;
boardSquare.Location.Y = (int)args.NewValue;
boardSquare.resetBackgroundColorToPosition();
})));
}
public BoardSquare()
{
InitializeComponent();
Location = new BoardLocation(Int32.MinValue, Int32.MinValue);
}
private void resetBackgroundColorToPosition()
{
this.Background = (Brush)(new ColorEnumToBrushesConverter()).Convert(Location.GetSquareColor(), typeof(BlackWhiteColor), null, null);
}
public static readonly DependencyProperty XPositionProperty;
public static readonly DependencyProperty YPositionProperty;
public int XPosition
{
get
{
return (int)GetValue(XPositionProperty);
}
set
{
SetValue(XPositionProperty, value);
}
}
public int YPosition
{
get
{
return (int)GetValue(YPositionProperty);
}
set
{
SetValue(YPositionProperty, value);
}
}
public BoardLocation Location { get; set; }
}

The first argument of PropertyChangedCallback is the local instance (btw. you better name it obj than value to avoid confusion). You have to cast this DependencyObject to BoardSquare and that's all.
public static readonly DependencyProperty XPositionProperty =
DependencyProperty.Register("XPosition", typeof(int), typeof(BoardSquare),
new PropertyMetadata(new PropertyChangedCallback((obj, args) => {
BoardSquare bs = obj as BoardSquare;
bs.Location.X = (int)args.NewValue;
bs.resetBackgroundColorToPosition();
})));

If I understand your question correctly, you are trying to override already WPF certificate property with your own. I don't think that's necessary here. If XPosition is already WPF certificate property, all you have to do is create a property in your usercontrol with getter/setter with setter calling INotifypropertychanged. you don't need dependency property in this case unless you want only same name but behave differently, and why do you want that?.