I'm currently doing some rescaling on data in a valueconverter whenever a panel is redrawn. I want to move some of this processing to the viewmodel as the most of the processing only occurs if the control size or a few other properties change.
To ensure the rescaled data looks acceptable I need the ActualWidth of the container in the viewmodel. I want to bind it to a property of the viewmodel one way so when it changes I can trigger the rescaling processing.
All the examples I could find bind a CLR or dependency property to an element rather than the other way and I'm clearly missing something in my understanding to work out how I should do it. I have have tried a few different things setting up the binding but am just not getting it right.
Any hints? thanks.
In MyView XAML:
<myItemsControl/>
In MyView code behind, something like:
Binding b = new Binding(MyWidthProperty);
b.Mode = BindingMode.OneWay;
b.Source = myItemsControl.Name;
.........?
and
public static readonly DependencyProperty MyWidthProperty =
DependencyProperty.Register( "MyWidth", typeof(Double), typeof(MyViewModel));
In MyViewModel:
public Double MyWidth{
get { return _myWidth; }
set { _myWidth = value; ViewChanged(this); } }
You cannot do it this way. You cannot set a Binding to ActualWidth, as it's read-only.
You can only set a binding to MyWidth. But for this, you need first to convert MyWidth into a DependencyProperty. Then you will be able to do something like
Binding b = new Binding("ActualWidth") { Source = myItemsControl };
this.SetBinding(MyViewModel.MyWidthProperty, b);
For converting into a dependency property, you'll need to replace your definition of MyWidth with the following:
public static readonly DependencyProperty MyWidthProperty =
DependencyProperty.Register("MyWidth", typeof(double), typeof(MyViewModel),
new UIPropertyMetadata(
0.0,
(d, e) =>
{
var self = (MyViewModel)d;
ViewChanged(self);
}));
But be careful with dependency properties; it's better to read the documentation first.
Edit: You would also need to define the property this way:
public double MyWidth
{
get { return (double)this.GetValue(MyWidthProperty); }
set { this.SetValue(MyWidthProperty, value); }
}
Related
If I create a custom control like this:
public class MyControl : ContentControl
{
public static readonly DependencyProperty ItemsProperty =
DependencyProperty.Register(
"Items",
typeof(ObservableCollection<object>),
typeof(MyControl),
new PropertyMetadata(null));
public MyControl()
{
// Setup a default value to empty collection
// so users of MyControl can call MyControl.Items.Add()
Items = new ObservableCollection<object>();
}
public ObservableCollection<object> Items
{
get { return (ObservableCollection<object>)GetValue(ItemsProperty); }
set { SetValue(ItemsProperty, value); }
}
}
And then allow the user to bind to it in Xaml like this:
<DataTemplate>
<MyControl Items="{Binding ItemsOnViewModel}"/>
</DataTemplate>
Then the binding never works! This is due to the Dependency Property Precedence, which puts CLR Set values above Template bindings!
So, I understand why this isn't working, but I wonder if there is a solution. Is it possible to provide a default value of ItemsProperty to new ObservableCollection for lazy consumers of MyControl that just want to add Items programmatically, while allowing MVVM power-users of My Control to bind to the same property via a DataTemplate?
This is for Silverlight & WPF. DynamicResource setter in a style seemed like a solution but that won't work for Silverlight :(
Update:
I can confirm SetCurrentValue(ItemsProperty, new ObservableCollection<object>()); does exactly what I want - in WPF. It writes the default value, but it can be overridden by template-bindings. Can anyone suggest a Silverlight equivalent? Easier said than done! :s
Another Update:
Apparently you can simulate SetCurrentValue in .NET3.5 using value coercion, and you can simulate value coercion in Silverlight using these techniques. Perhaps there is a (long-winded) workaround here.
SetCurrentValue workaround for .NET3.5 using Value Coercion
Value Coercion workaround for Silverlight
Can't you just specify the default property of the dependency property:
public static readonly DependencyProperty ItemsProperty = DependencyProperty.Register(
"Items",
typeof(ObservableCollection<object>),
typeof(CaseDetailControl),
new PropertyMetadata(new ObservableCollection<object>()));
or am I missing what you are after?
Edit:
ah... in that case how about checking for null on the getter?:
public ObservableCollection<object> Items
{
get
{
if ((ObservableCollection<object>)GetValue(ItemsProperty) == null)
{
this.SetValue(ItemsProperty, new ObservableCollection<object>());
}
return (ObservableCollection<object>)GetValue(ItemsProperty);
}
set
{
this.SetValue(ItemsProperty, value);
}
}
When ObservableCollection properties misbehave, I try throwing out assignments to that property. I find that the references don't translate right and bindings get lost, somehow. As a result, I avoid actually setting ObservableCollection properties (preferring, instead, to clear the existing property and add elements to it). This becomes really sloppy with a DependencyProperty because you're going to call your getter multiple times in your setter. You might want to consider using INotifyPropertyChanged instead. Anyway, here's what it'd look like:
EDIT: Blatantly stole the getter from SteveL's answer. I reworked it a touch so that you only have a single call to GetValue, is all. Good work around.
public ObservableCollection<object> Items
{
get
{
ObservableCollection<object> coll = (ObservableCollection<object>)GetValue(ItemsProperty);
if (coll == null)
{
coll = new ObservableCollection<object>();
this.SetValue(ItemsProperty, coll);
}
return coll;
}
set
{
ObservableCollection<object> coll = Items;
coll.Clear();
foreach(var item in value)
coll.Add(item);
}
}
Note that this is depending on your default to set correctly. That means changing the static ItemsProperty default to be a new ObservableCollection of the correct type (i.e. new PropertyMetadata(new ObservableCollection()). You'll also have to remove that setter in the constructor. And note, I've no idea if that'll actually work. If not, you'll want to move to using INotifyPropertyChanged for sure...
I have a dependency property on a class inheriting from adorner, like so:
public class LoadingAdorner : Adorner
{
public static readonly DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof (string), typeof (LoadingAdorner), new PropertyMetadata(default(string)));
public string Text
{
get { return (string) GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
public static readonly DependencyProperty IsShowingProperty = DependencyProperty.Register("IsShowing", typeof (bool), typeof (LoadingAdorner), new PropertyMetadata(default(bool)));
...
}
Adorner's don't really have any XAML, but I wanted the text of this adorner to be bindable to the viewmodel. So I create the binding in code, in the view's constructor, like so:
private readonly LoadingAdorner _loading;
public MainWindow()
{
InitializeComponent();
_loading = new LoadingAdorner(MainPage);
var bind = new Binding("LoadingText"){Source = DataContext};
_loading.SetBinding(LoadingAdorner.TextProperty, bind);
}
The DataContext is my view model, my view model implements INotifyPropertyChanged, LoadingText is a string property that calls OnPropertyChanged, etc. All bindings in XAML work fine, however, the code binding does not.
I believe it is because at the time of creating the binding, the view model has not yet been set to the DataContext (it is null), I do this on the line after creating the view. If I set this binding to a property on my view using Source = this, it works.
My question is, why are the XAML bindings are capable of reacting to the source object changing, while the code binding doesn't appear to be? Is there a proper way for me to create a binding that will react to this similiar to the XAML bindings?
Binding do not and cannot react to source changes, it is a logical impossibility, objects do not change properties and references to objects change. Bindings can react to DataContext property changes but only if you do not do something horrible like Source = DataContext which kills the mechanism by getting the current data context once only. Just drop that so the DataContext is the default source again and the binding should react to the changes.
If the DataContext is on another object than the one that is bound it needs to be moved into the Path, i.e. new Binding("DataContext.LoadingText"){ Source = this }.
I'm trying to create a custom markup extension using IMarkupExtension<T> that has some DependencyProperties for binding. However, I am struggling to resolve the problem of the markup extension being resolved at XAML parse time, and the bindings only later. I don't seem to ever get something through the bindings: they're always null and never call their change callback.
The docs mention something about returning the instance of the markup extension (under "Returning the Current Markup Extensions Instance"), but that seems to make stuff explode because it's the wrong type for the target. This SL5 MultiBinding seems to return a proxy binding to an internal source object, but I can't manage to get that working: my bindings still don't ever set.
I can't seem to find any solid information how how to actually implement markup extensions with DependencyProperties (even though it seemed like something a lot of people were excited about with SL5...). Can anyone offer any guidance or tutorials?
Specifically, what I'm trying to do is create a markup extension that can dynamically construct a path to do a binding to a list, like so:
{my:ListLookup ListPath='List' Index={Binding Index}}
I'm wanting it to basically output a Binding that would look like {Binding List[Index]}, where Index is dynamic. The purpose of doing this over, say, a MultiBinding on the list and index, is so that we are binding directly to the object and get change notifications. (If there's a better way of doing this...)
I've fiddled with this a lot more and I've found the solution. It's based on the implementation of the SL5 MultiBinding that I linked to in the question.
The trick is that a Binding on a MarkupExtension will never be evaluated because it doesn't have a DataContext or something, but if you take the BindingExpression from it and throw it into a proxy Attached Property (attached to the target object) then you can get the Binding to resolve.
Below is a simple MarkupExtension that demonstrates this. All it's doing is taking a single Binding and outputting its value (obeying changes appropriately), but it shows how it holds together. This can be extended to solve the dictionary issue I was talking about, along with this problem in general.
public class SimpleBindingMarkupExtension : DependencyObject, IMarkupExtension<object>, INotifyPropertyChanged
{
public object Binding
{
get { return (object)GetValue(BindingProperty); }
set { SetValue(BindingProperty, value); }
}
public static readonly DependencyProperty BindingProperty =
DependencyProperty.Register(
"Binding",
typeof(object),
typeof(SimpleBindingMarkupExtension),
new PropertyMetadata(null));
public static readonly DependencyProperty ProxyAttachedBindingProperty =
DependencyProperty.RegisterAttached(
"ProxyAttachedBinding",
typeof(object),
typeof(SimpleBindingMarkupExtension),
new PropertyMetadata(null, OnProxyAttachedBindingChanged));
public static readonly DependencyProperty AttachedMarkupExtensionProperty =
DependencyProperty.RegisterAttached(
"AttachedMarkupExtension",
typeof(SimpleBindingMarkupExtension),
typeof(SimpleBindingMarkupExtension),
new PropertyMetadata(null));
private object _bindingSource;
public object BindingSource
{
get { return _bindingSource; }
set
{
_bindingSource = value;
OnPropertyChanged("BindingSource");
}
}
private static void OnProxyAttachedBindingChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// Pull the MarkupExtension from the attached property
var markupExtension = (SimpleBindingMarkupExtension) d.GetValue(AttachedMarkupExtensionProperty);
markupExtension.ProxyAttachedBindingChanged(e.NewValue);
}
private void ProxyAttachedBindingChanged(object value)
{
BindingSource = value;
}
public object ProvideValue(IServiceProvider serviceProvider)
{
IProvideValueTarget target = (IProvideValueTarget) serviceProvider.GetService(typeof (IProvideValueTarget));
DependencyObject targetObject = target.TargetObject as DependencyObject;
if (targetObject == null)
return null;
// Attach this MarkupExtension to the object so we can find it again from attached property change callbacks
targetObject.SetValue(AttachedMarkupExtensionProperty, this);
// Put binding onto proxy attached property, so it actually evaluates
var localValue = ReadLocalValue(BindingProperty);
var bindingExpression = localValue as BindingExpression;
if (bindingExpression == null)
{
return localValue;
}
Binding originalBinding = bindingExpression.ParentBinding;
BindingOperations.SetBinding(targetObject, ProxyAttachedBindingProperty, originalBinding);
// Give the target a proxy Binding that binds to a property on the MarkupExtension
Binding binding = new Binding
{
Path = new PropertyPath("BindingSource"),
Source = this
};
return binding.ProvideValue(serviceProvider);
}
#region INotifyPropertyChanged
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}
Usage:
<TextBlock Text="{local:SimpleBindingMarkupExtension Binding={Binding Text}}"/>
As mentioned, this example will produce the same result as just saying Text="{Binding Text}", but shows the solution.
I am working on a custom MarkupExtension in which I need a non string parameters from XAML to construct the new object. Is it possible to use a non-string parameter binding on a field in DataContext scope?
In other words, how can I do something like this?
<ListBox ItemsSource="{Binding Source={local:MyMarkupExtension {x:Type Button},IncludeMethods={Binding Source=CustomerObject.IsProblematic}}}" />
where IncludeMethods=CustomerObject.IsProblematic give me this error:
Binding cannot be set on the 'IncludeMethods' property of type 'TypeDescriptorExtension'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.
Can anyone help me?
thanks
A 'Binding' can only be set on a DependencyProperty of a DependencyObject - it is true. The problem is that MarkupExtension class does not derive from DependencyObject, that's why it is not possible to set binding on it's properties.
[EDIT]
Workaround is using ValueConverters. Another workaround is to change C# language to allow multiple inheritance. By the way, in Silverlight MarkupExtension implements IMarkupExtension interface, so I tried to implement it in my custom extension and derive it from DependecyObject, added DependencyProperty there and set binding to it. It doesn't crash, but the binding is actually set after ProvideValue() is called. So even in Silverlight there's no solution (or it is difficult - see link provided in Klaus78's answer). In WPF MarkupExtension doesn't implement any interface, so you cannot bind to it's properties.
So as other have said, please first consider using a ValueConverter. This is the proper approach for manipulating bindings.
If however, you still want to use a MarkupExtension with bindings to the view-model or data context then you can create the binding manually in the markup extension class. This is similar to the approach taken by #nicolay.anykienko but we don't need to create an attached property.
As an example, I have created a currency symbol markup extension. The default behaviour is to use the CultureInfo.CurrentCulture but a few view-models have their own CultureInfo property that are different from the current culture. So for these view-models the XAML needs to bind to this property. Note that this could easily be done with a Converter instead, but for the sake of an example here is the markup extension:
public class CurrencySymbolExtension : MarkupExtension
{
public override object ProvideValue(IServiceProvider serviceProvider)
{
var targetProvider = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
var targetElement = targetProvider.TargetObject as FrameworkElement;
var targetProperty = targetProvider.TargetProperty as DependencyProperty;
if (!String.IsNullOrEmpty(CultureBindingPath) &&
targetElement != null &&
targetProperty != null)
{
// make sure that if the binding context changes then the binding gets updated.
targetElement.DataContextChanged +=
(sender, args) => ApplyBinding(targetElement, targetProperty, args.NewValue);
// apply a binding to the target
var binding = ApplyBinding(targetElement, targetProperty, targetElement.DataContext);
// return the initial value of the property
return binding.ProvideValue(serviceProvider);
}
else
{
// if no culture binding is provided then use the current culture
return CultureInfo.CurrentCulture.NumberFormat.CurrencySymbol;
}
}
private Binding ApplyBinding(DependencyObject target, DependencyProperty property, object source)
{
BindingOperations.ClearBinding(target, property);
var binding = new Binding(CultureBindingPath + ".NumberFormat.CurrencySymbol")
{
Mode = BindingMode.OneWay,
Source = source,
FallbackValue = CultureInfo.CurrentCulture.NumberFormat.CurrencySymbol,
};
BindingOperations.SetBinding(target, property, binding);
return binding;
}
public string CultureBindingPath { get; set; }
}
This then gets used as follows:
<!-- Standard Usage -->
<TextBlock Text="{local:CurrencySymbol}"/>
<!-- With DataContext Binding -->
<TextBlock Text="{local:CurrencySymbol CultureBindingPath=ViewModelCulture}"/>
Where ViewModelCulture is the property on the view-model being used as the source of the binding.
I found a workaround for this problem.
The main idea is to define attached property for each parameter that requires binding.
public class MarkupExtensionWithBindableParam : MarkupExtension
{
public BindingBase Param1 { get; set; } // its necessary to set parameter type as BindingBase to avoid exception that binding can't be used with non DependencyProperty
public override object ProvideValue(IServiceProvider serviceProvider)
{
IProvideValueTarget target = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
DependencyObject targetObject;
DependencyProperty targetProperty;
if (target != null && target.TargetObject is DependencyObject && target.TargetProperty is DependencyProperty)
{
targetObject = (DependencyObject)target.TargetObject;
targetProperty = (DependencyProperty)target.TargetProperty;
}
else
{
return this; // magic
}
// Bind the Param1 to attached property Param1BindingSinkProperty
BindingOperations.SetBinding(targetObject, MarkupExtensionWithBindableParam.Param1BindingSinkProperty, Param1);
// Now you can use Param1
// Param1 direct access example:
object param1Value = targetObject.GetValue(Param1BindingSinkProperty);
// Param1 use in binding example:
var param1InnerBinding = new Binding() { Source = targetObject, Path = new PropertyPath("(0).SomeInnerProperty", Param1BindingSinkProperty) }); // binding to Param1.SomeInnerProperty
return param1InnerBinding.ProvideValue(serviceProvider); // return binding to Param1.SomeInnerProperty
}
private static DependencyProperty Param1BindingSinkProperty = DependencyProperty.RegisterAttached("Param1BindingSink", typeof(object)// set the desired type of Param1 for at least runtime type safety check
, typeof(MarkupExtensionWithBindableParam ), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits));
}
Usage is straightforward:
<TextBlock Text="{local:MarkupExtensionWithBindableParam Param1={Binding Path='SomePathToParam1'}}"/>
This link is informative about
Custom Markup Extension with bindable properties
EDITSomeone made me note that this works only for Silverlight, because in WPF MarkupExtension doesn't implement IMarkupExtension interface. (Thank you EvAlex)
I have an issue similar to the following post:
Silverlight DataGridTextColumn Binding Visibility
I need to have a Column within a Silverlight DataGrid be visibile/collapsed based on a value within a ViewModel. To accomplish this I am attempting to Bind the Visibility property to a ViewModel. However I soon discovered that the Visibility property is not a DependencyProperty, therefore it cannot be bound.
To solve this, I attempted to subclass my own DataGridTextColumn. With this new class, I have created a DependencyProperty, which ultimately pushes the changes to the DataGridTextColumn.Visibility property. This works well, if I don't databind. The moment I databind to my new property, it fails, with a AG_E_PARSER_BAD_PROPERTY_VALUE exception.
public class MyDataGridTextColumn : DataGridTextColumn
{
#region public Visibility MyVisibility
public static readonly DependencyProperty MyVisibilityProperty =
DependencyProperty.Register("MyVisibility", typeof(Visibility), typeof(MyDataGridTextColumn), new PropertyMetadata(Visibility.Visible, OnMyVisibilityPropertyChanged));
private static void OnMyVisibilityPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var #this = d as MyDataGridTextColumn;
if (#this != null)
{
#this.OnMyVisibilityChanged((Visibility)e.OldValue, (Visibility)e.NewValue);
}
}
private void OnMyVisibilityChanged(Visibility oldValue, Visibility newValue)
{
Visibility = newValue;
}
public Visibility MyVisibility
{
get { return (Visibility)GetValue(MyVisibilityProperty); }
set { SetValue(MyVisibilityProperty, value); }
}
#endregion public Visibility MyVisibility
}
Here is a small snippet of the XAML.
<DataGrid ....>
<DataGrid.Columns>
<MyDataGridTextColumn Header="User Name"
Foreground="#FFFFFFFF"
Binding="{Binding User.UserName}"
MinWidth="150"
CanUserSort="True"
CanUserResize="False"
CanUserReorder="True"
MyVisibility="{Binding Converter={StaticResource BoolToVisibilityConverter}, Path=ShouldShowUser}"/>
<DataGridTextColumn .../>
</DataGrid.Columns>
</DataGrid>
A couple important facts.
The Converter is indeed defined above in the local resources.
The Converter is correct, it is used many other places in the solution.
If I replace the {Binding} syntax for the MyVisibility property with "Collapsed" the Column does in fact disappear.
If I create a new DependencyProperty (i.e. string Foo), and bind to it I receive the AG_E_PARSER_BAD_PROPERTY_VALUE exception too.
Does anybody have any ideas as to why this isn't working?
Here's the solution I've come up with using a little hack.
First, you need to inherit from DataGrid.
public class DataGridEx : DataGrid
{
public IEnumerable<string> HiddenColumns
{
get { return (IEnumerable<string>)GetValue(HiddenColumnsProperty); }
set { SetValue(HiddenColumnsProperty, value); }
}
public static readonly DependencyProperty HiddenColumnsProperty =
DependencyProperty.Register ("HiddenColumns",
typeof (IEnumerable<string>),
typeof (DataGridEx),
new PropertyMetadata (HiddenColumnsChanged));
private static void HiddenColumnsChanged(object sender,
DependencyPropertyChangedEventArgs args)
{
var dg = sender as DataGrid;
if (dg==null || args.NewValue == args.OldValue)
return;
var hiddenColumns = (IEnumerable<string>)args.NewValue;
foreach (var column in dg.Columns)
{
if (hiddenColumns.Contains ((string)column.GetValue (NameProperty)))
column.Visibility = Visibility.Collapsed;
else
column.Visibility = Visibility.Visible;
}
}
}
The DataGridEx class adds a new DP for hiding columns based on the x:Name of a DataGridColumn and its descendants.
To use in your XAML:
<my:DataGridEx x:Name="uiData"
DataContext="{Binding SomeDataContextFromTheVM}"
ItemsSource="{Binding Whatever}"
HiddenColumns="{Binding HiddenColumns}">
<sdk:DataGridTextColumn x:Name="uiDataCountOfItems">
Header="Count"
Binding={Binding CountOfItems}"
</sdk:DataGridTextColumn>
</my:DataGridEx>
You need to add these to your ViewModel or whatever data context you use.
private IEnumerable<string> _hiddenColumns;
public IEnumerable<string> HiddenColumns
{
get { return _hiddenColumns; }
private set
{
if (value == _hiddenColumns)
return;
_hiddenColumns = value;
PropertyChanged (this, new PropertyChangedEventArgs("HiddenColumns"));
}
}
public void SomeWhereInYourCode ()
{
HiddenColumns = new List<string> {"uiDataCountOfItems"};
}
To unhide, you only need to remove the corresponding name from the list or recreate it without the unhidden name.
I have another solution to this problem that uses an approach similar to the "Binding" property that you find on DataGridTextColumn. Since the column classes are DependencyObjects, you can't directly databind to them, BUT if you add a reference to a FrameworkElement that implements INotifyPropertyChanged you can pass a databinding through to the element, and then use a dependency property to notify the Column that the databinding has changed.
One thing to note is that having the binding on the Column itself instead of the Grid will probably mean that you will want to use a DataContextProxy to get access to the field that you want to bind the Visibility to (the column binding will default to the scope of the ItemSource).
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
namespace XYZ.Controls
{
public class ExtendedDataGridTextColumn : DataGridTextColumn
{
private readonly Notifier _e;
private Binding _visibilityBinding;
public Binding VisibilityBinding
{
get { return _visibilityBinding; }
set
{
_visibilityBinding = value;
_e.SetBinding(Notifier.MyVisibilityProperty, _visibilityBinding);
}
}
public ExtendedDataGridTextColumn()
{
_e = new Notifier();
_e.PropertyChanged += ToggleVisibility;
}
private void ToggleVisibility(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "Visibility")
this.Visibility = _e.MyVisibility;
}
//Notifier class is just used to pass the property changed event back to the column container Dependency Object, leaving it as a private inner class for now
private class Notifier : FrameworkElement, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public Visibility MyVisibility
{
get { return (Visibility)GetValue(MyVisibilityProperty); }
private set { SetValue(MyVisibilityProperty, value); }
}
public static readonly DependencyProperty MyVisibilityProperty = DependencyProperty.Register("MyVisibility", typeof(Visibility), typeof(Notifier), new PropertyMetadata(MyVisibilityChanged));
private static void MyVisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var n = d as Notifier;
if (n != null)
{
n.MyVisibility = (Visibility) e.NewValue;
n.PropertyChanged(n, new PropertyChangedEventArgs("Visibility"));
}
}
}
}
}
The datagrid column inherits from DependencyObject instead of FrameworkElement. In WPF this would be no big deal... but in silverlight you can only bind to FrameworkElement objects. So you get the descriptive error message of AG_E_PARSER_BAD_PROPERTY_VALUE when you try.
I don't know how much this will help, but I've run into the lack of dependency property problem with data grid columns myself in my latest project. What I did to get around it, was to create an event in the grid column view model, then when the grid is being assembled in the client, use a closure to subscribe the grid column to the column view model. My particular problem was around width. It starts with the view model class for the grid column, which looks something like this pseudo-code:
public delegate void ColumnResizedEvent(double width);
public class GridColumnViewModel : ViewModelBase
{
public event ColumnResizedEvent ColumnResized;
public void Resize(double newContainerWidth)
{
// some crazy custom sizing calculations -- don't ask...
ResizeColumn(newWidth);
}
public void ResizeColumn(double width)
{
var handler = ColumnResized;
if (handler != null)
handler(width);
}
}
Then there's the code that assembles the grid:
public class CustomGrid
{
public CustomGrid(GridViewModel viewModel)
{
// some stuff that parses control metadata out of the view model.
// viewModel.Columns is a collection of GridColumnViewModels from above.
foreach(var column in viewModel.Columns)
{
var gridCol = new DataGridTextColumn( ... );
column.ColumnResized += delegate(double width) { gridCol.Width = new DataGridLength(width); };
}
}
}
When the datagrid is resized in the application, the resize event is picked up and calls the resize method on the viewmodel the grid is bound to. This in turn calls the resize method of each grid column view model. The grid column view model then raises the ColumnResized event, which the data grid text column is subscribed to, and it's width is updated.
I realise this isn't directly solving your problem, but it was a way I could "bind" a view model to a data grid column when there are no dependency properties on it. The closure is a simple construct that nicely encapsulates the behaviour I wanted, and is quite understandable to someone coming along behind me. I think it's not too hard to imagine how it could be modified to cope with visibility changing. You could even wire the event handler up in the load event of the page/user control.
Chris Mancini,
you do not create binding to "Binding" property of data grid column. Well, you write "{Binding User.UserName}", but it doesn't create binding, because (as zachary said) datagrid column doesn't inherit from FrameworkElement and hasn't SetBinding method.
So expression "{Binding User.UserName}" simply creates Binding object and assign it to Binding property of column (this property is type of Binding).
Then datagrid column while generates cells content (GenerateElement - protected method) uses this Binding object to set binding on generated elements (e.g. on Text property of generated TextBlock) which are FrameworkElements
GreatTall1's solution is great, but it need to bit change to make it work.
var n = d as Notifier;
if (n != null)
{
//Assign value in the callback will break the binding.
//n.MyVisibility = (Visibility)e.NewValue;
n.PropertyChanged(n, new PropertyChangedEventArgs("Visibility"));
}
Note that the problem isn't just as simple as 'Visibility' not being a dependency property. In a DataGrid the columns aren't part of the visual 'tree' so you can't use AncestorType even in WPF (or Silverlight 5).
Here's a couple WPF related links (please comment if any of these work for Silverlight - sorry I don't have time to test now)
Has a really nice explanation of the problem and failures of certain solutions (and a clever solution):
http://tomlev2.wordpress.com/2011/03/21/wpf-how-to-bind-to-data-when-the-datacontext-is-not-inherited/
And a couple StackOverflow questions:
WPF Hide DataGridColumn via a binding
Binding Visible property of a DataGridColumn in WPF DataGrid
This works on a data grid template column:
public class ExtendedDataGridColumn : DataGridTemplateColumn
{
public static readonly DependencyProperty VisibilityProperty = DependencyProperty.Register("Visibility", typeof(Visibility), typeof(DataGridTemplateColumn), new PropertyMetadata(Visibility.Visible, VisibilityChanged));
public new Visibility Visibility
{
get { return (Visibility)GetValue(VisibilityProperty); }
set { SetValue(VisibilityProperty, value); }
}
private static void VisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if ((DataGridTemplateColumn)d != null)
{
((DataGridTemplateColumn)d).Visibility = (Visibility)e.NewValue;
}
}
}
From your MyDataGridTextColumn class, you could get the surrounding DataGrid.
Then you get your ViewModel out of the DataContext of the DataGrid and add a handler to the PropertyChanged event of your ViewModel. In the handler you just check for the property name and its value and change the Visibility of the Column accordingly.
Its not quite the best solution, but it should work ;)