I am having trouble setting a property of a custom user control using a DependencyProperty through databinding on the parent UserControl.
Here is the code for my custom UserControl:
public partial class UserEntityControl : UserControl
{
public static readonly DependencyProperty EntityProperty = DependencyProperty.Register("Entity",
typeof(Entity), typeof(UserEntityControl));
public Entity Entity
{
get
{
return (Entity)GetValue(EntityProperty);
}
set
{
SetValue(EntityProperty, value);
}
}
public UserEntityControl()
{
InitializeComponent();
PopulateWithEntities(this.Entity);
}
}
I want access to the Entity property in the code behind because that will dynamically build the user control based on values stored in the Entity. The problem that I am having is that the Entity property is never set.
Here is how I am setting up the binding in the parent user control:
<ListBox Grid.Row="1" Grid.ColumnSpan="2" ItemsSource="{Binding SearchResults}" x:Name="SearchResults_List">
<ListBox.ItemTemplate>
<DataTemplate>
<!--<views:SearchResult></views:SearchResult>-->
<eb:UserEntityControl Entity="{Binding}" ></eb:UserEntityControl>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I am setting the ItemsSource of the ListBox to SearchResults, which is an Observable Collection of Entities (The same type as Entity on the custom UserControl).
I am not getting any runtime binding errors in the debug output window. I just cannot set the value of the Entity property. Any ideas?
You are trying to use the Entity property in the c-tor, which is too soon. the c-tor is going to be fired BEFORE the property value is going to be given.
What u need to do is to add a propertyChanged Event HAndler to the DependencyProperty, like so:
public static readonly DependencyProperty EntityProperty = DependencyProperty.Register("Entity",
typeof(Entity), typeof(UserEntityControl), new PropertyMetadata(null, EntityPropertyChanged));
static void EntityPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var myCustomControl = d as UserEntityControl;
var entity = myCustomControl.Entity; // etc...
}
public Entity Entity
{
get
{
return (Entity)GetValue(EntityProperty);
}
set
{
SetValue(EntityProperty, value);
}
}
Related
I have the object MyObject Object in the class MainClass.xaml.
I want to pass this object to a ViewModel class of a nested user control called SubSubUserControl through a SubUserControl.
Here is the code in MainClass.xaml:
<UserControl x:Class="Test.SubUserControl"
d:DataContext="{d:DesignInstance d:Type=local:SubUserControlViewModel}">
<Grid>
<local:SubSubUserControl Object="{Binding Object, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:SubUserControl}}}"/>
</Grid>
</UserControl>
In SubUserControl I have a classical DependencyProperty in order to pass Object to it.
public static readonly DependencyProperty ObjectProperty = DependencyProperty.Register(nameof(Object), typeof(Object), typeof(SubUserControl));
public Object Object
{
get => (Object)GetValue(ObjectProperty);
set => SetValue(ObjectProperty, value);
}
protected override void OnInitialized(EventArgs e)
{
InitializeComponent();
DataContext = new SubUserControlViewModel(Object);
base.OnInitialized(e);
}
SubUserControl is only a "bridge", the object Object is needed in SubSubUserControl.
I pass to it with a binding (changing Datacontex beacause the standard DataContext for SubUserControl is his ViewModel).
<local:SubSubUserControl Object="{Binding Object, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}" />
and SubSubUserControl has the classical DependencyProperty.
SubSubUserControl has a ViewModel as DataContext and I'd like to pass that object to it.
I try with
public static readonly DependencyProperty ObjectProperty = DependencyProperty.Register(nameof(Object), typeof(Object), typeof(SubSubUserControl));
public Object Object
{
get => (Object)GetValue(ObjectProperty);
set => SetValue(ObjectProperty, value);
}
protected override void OnInitialized(EventArgs e)
{
InitializeComponent();
DataContext = new SubSubUserControlViewModel(Object);
base.OnInitialized(e);
}
but Object is null.
The same code in SubUserControl works.
Is there a way to pass an object using binding to a ViewModel class that belongs to a nested UserControl?
I saw a lot of similar questions but noone works with my specific case...
EDIT
The class Object is instanced code-behind in MainClass.xaml.cs. In order to pass it I set the DataContext of MainClass to Self.
public MyObject Object { get; set; } = new MyObject();
Here is how I set DataContext in MainClass.xaml
<Window x:Class="Test.MainWindow"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
<local:SubUserControl Object="{Binding Object}"/>
</Grid>
</Window>
Setting the DataContext to the entire Window avoid me to write something like ElementName or Relative Source.
P.s. Resharper do not warn me about any DataContext, each instance is seen correctly.
I don't know the method OnInitialized, but from the documentation :
Raises the Initialized event.
And the event Initialized :
Whether you choose to handle Loaded or Initialized depends on your requirements. If you do not need to read element properties, intend to reset properties, and do not need any layout information, Initialized might be the better event to act upon. If you need all properties of the element to be available, and you will be setting properties that are likely to reset the layout, Loaded might be the better event to act upon.
I think the binding work, but you try to read the value in OnInitialized that is called before the binding is resolved.
As suggested in the documentation, maybe you can use the event Loaded like :
public partial class SubSubUserControl : UserControl
{
public SubSubUserControl()
{
InitializeComponent();
Loaded += SubSubControl_Loaded;
}
private void SubSubControl_Loaded(object sender, RoutedEventArgs e)
{
DataContext = new SubSubViewModel(TargetFoo);
}
}
A alternative is to update the data context when the dependency property is modified :
public partial class SubSubUserControl : UserControl
{
public static readonly DependencyProperty ObjectProperty = DependencyProperty.Register(
"Object", typeof(MyObject),
typeof(SubSubUserControl),
new PropertyMetadata(OnObjectChanged)
);
private static void OnObjectChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if(sender is SubSubControl ssc)
{
ssc.DataContext = new SubSubViewModel((MyObject)e.NewValue);
}
}
}
EDIT from exchanges in comments.
It looks like you have a binding problem too. I suspect that a other element of type UserControl encapsulate the SubSubUserControl, like :
MainClass
SubUserControl
OtherUserControl
SubSubUserControl
In this case, the binding will use OtherUserControl as source (and not the expected SubUserControl).
In this case, you can specify in the binding the source's type is SubUserControl to avoid a other element of type UserControl is selected :
<local:SubSubUserControl Object="{Binding BridgeFoo, RelativeSource={RelativeSource AncestorType={x:Type local:SubUserControl}}}" />
A alternative is to use Binding.ElementName instead of Binding.RelativeSource :
<UserControl x:Class="ProjectNamespace.SubUserControl"
...
xmlns:local="clr-namespace:ProjectNamespace"
Name="Sub">
<local:SubSubUserControl Object="{Binding Object, ElementName=Sub}" />
</UserControl>
I prefer this, because I never remember the RelativeSource syntax.
I have creted my User Control where I would like to make posibility to bind a UIElement. My user control:
public partial class TextArea : UserControl
{
public UIElement AncestorContainer
{
get => (UIElement)GetValue(AncestorContainerProperty);
set => SetValue(AncestorContainerProperty, value);
}
public TextArea()
{
InitializeComponent();
DataContext = this;
}
public static readonly DependencyProperty AncestorContainerProperty =
DependencyProperty.Register("AncestorContainerProperty", typeof(UIElement), typeof(TextArea), new PropertyMetadata(null));
}
When creating my UserControl in C# it is working fine - no exceptions like this:
var textArea = new TextArea
{
AncestorContainer = Root, // Root is name of Grid
Text = textItem.Text
};
However when trying to use binding in XAML I get an exception:
<ItemsControl ItemsSource="{Binding SuggestedTexts}" >
<ItemsControl.ItemTemplate>
<DataTemplate>
<components:TextArea
AncestorContainer="{Binding ElementName=Sidebar}"/> <!-- Side bar is name of Grid above in XAML -->
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
And the exception:
"Binding" cannot be set in the "ParentContainer" type "TextArea".
"Binding" can only be set in the properties of the DependencyProperty
object DependencyObject.
You have a typo declaring dependency property as you have written
DependencyProperty.Register("AncestorContainerProperty", ...
which should be replaced by
DependencyProperty.Register("AncestorContainer", ...
or better
DependencyProperty.Register(nameof(AncestorContainer), ...
WPF .NET4.5
The Problem: When the ListSource dependency property on the ImageCanvas is set, only the last behavior, "MyList", actually gets updated. It is as if the last behavior overwrites all the previous bindings.
How can I have all the behaviors updated when the ListSource on the ImageCanvas is updated?
I have a custom control with a ListSource dependency property:
public class ImageCanvas : ContentControl
{
public FrameElement ListSource
{
get { return (FrameElement)GetValue(ListSourceProperty); }
set { SetValue(ListSourceProperty, value); }
}
// Using a DependencyProperty as the backing store for ListSource. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ListSourceProperty =
DependencyProperty.Register("ListSource", typeof(FrameElement), typeof(ImageCanvas),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
(s,e) =>
{
// The ListBehavior will be called before this dependency property of ImageCanvas.
ImageCanvas ic = s as ImageCanvas;
ic.Content = ((FrameElement)e.NewValue).DataContext;
}
));
}
}
The XAML is:
<ctrl:ImageCanvas x:Name="ImageCanvas"
Grid.Column="1" Grid.Row="1" Background="Aquamarine"
Panel.ZIndex="{Binding ImageLayer.ZIndex}"
Visibility="{Binding ImageLayer.Visibility}"
>
<i:Interaction.Behaviors>
<b:ImageCanvasBehavior x:Name="MyZoom" />
<b:MovieBehavior x:Name="MyMovie" />
<b:MusicBehavior x:Name="MyMusic" />
<b:ListBehavior x:Name="MyList" />
</i:Interaction.Behaviors>
</ctrl:ImageCanvas>
Each behavior is bound to the ListSource custom property of the ImageCanvas when the ImageCanvas is loaded by the XAML.
In the behaviors:
private void IC_Loaded(object sender, System.Windows.RoutedEventArgs e)
{
var ic = AssociatedObject as ImageCanvas;
var bindingListSource = new Binding();
bindingListSource.Source = this;
bindingListSource.Path = new PropertyPath(ListSourceProperty);
BindingOperations.SetBinding(ic, ImageCanvas.ListSourceProperty, bindingListSource);
}
public FrameElement ListSource
{
get { return (FrameElement)GetValue(ListSourceProperty); }
set { SetValue(ListSourceProperty, value); }
}
// Using a DependencyProperty as the backing store for ListSource. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ListSourceProperty =
DependencyProperty.Register("ListSource", typeof(FrameElement), typeof(ListBehavior), new PropertyMetadata(null,
(s,e) =>
{
var behavior = s as ListBehavior;
var ic = behavior.AssociatedObject as ImageCanvas;
if ((FrameElement)e.NewValue == (FrameElement)e.OldValue)
return;
CurrentFrame = ((FrameElement)e.NewValue).Frame;
}
));
The Problem: When the ListSource dependency property on the ImageCanvas is set, only the last behavior, "MyList", actually gets updated. It is as if the last behavior overwrites all the previous bindings.
How can I have all the behaviors updated when the ListSource on the ImageCanvas is updated?
Edit#1: To better explain, I have defined a "FrameElement" as:
public class FrameElement : UIElement
{
public object DataContext { get; set; }
public int Frame { get; set; }
public ListTypeEnum ListType { get; set; }
public string Title { get; set; }
}
The ContentControl is being used to display only one item at a time, DataTemplates in Resources are being used to implicitly change the display based on the DataContext (this works well). The DataContext may or may not have a collection, depending on what the DataContext is for the current display (hence the "Frame" number). The problem is that each behavior will need to determine if the current datacontext applies to itself--so each behavior, as listed in the XAML, needs to receive the current FrameElement when it is set on the ContentControl, i.e., the "ImageCanvas".
I hope that better explains my scenario.
TIA.
Edit#2:
If the BindingOperations are removed from the behaviors, and the XAML changed to directly bind, (see below), then all the behaviors are updated correctly! So the question now becomes, how can the XAML code be replicated correctly in the behavior to achieve the same result???
Working XAML code:
<ctrl:ImageCanvas x:Name="ImageCanvas"
Grid.Column="1" Grid.Row="1" Background="Aquamarine"
Panel.ZIndex="{Binding ImageLayer.ZIndex}"
Visibility="{Binding ImageLayer.Visibility}"
>
<i:Interaction.Behaviors>
<b:ImageCanvasBehavior x:Name="MyZoom"
ListSource="{Binding ElementName=ImageCanvas, Path=ListSource}" />
<b:MovieBehavior x:Name="MyMovie"
ListSource="{Binding ElementName=ImageCanvas, Path=ListSource}" />
<b:MusicBehavior x:Name="MyMusic"
ListSource="{Binding ElementName=ImageCanvas, Path=ListSource}" />
<b:ListBehavior x:Name="MyList"
ListSource="{Binding ElementName=ImageCanvas, Path=ListSource}" />
</i:Interaction.Behaviors>
</ctrl:ImageCanvas>
I'm currently developping an universal app in C#/XAML with MVVM (not MVVM Light) and I have trouble for the XAML part.
I'd like to display one or another StackPanel when a dependency property changed in my ViewModel. I think the code speaks for itself.
<StackPanel Visibility="{Binding MyProperty, Converter={StaticResource BooleanToVisibilityConverter}}">
<!-- Some content -->
</StackPanel>
<StackPanel Visibility="{Binding MyProperty, Converter={StaticResource InvertBooleanToVisibilityConverter}}">
<!-- Some another content -->
</StackPanel>
And here is the definition of the dependency property.
public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register(
"MyProperty",
typeof (bool),
typeof (MyViewModel),
new PropertyMetadata(true));
public bool MyProperty
{
get { return (bool) GetValue(MyPropertyProperty); }
set { SetValue(MyPropertyProperty, value); OnPropertyChanged(); // Implemented by ReSharper }
}
I guess you figure it out that MyProperty is a boolean that I convert into a Visibility via the converters. So, when MyProperty changed in the ViewModel, the view isn't updated.
I already tried to use the UpdateSourceTrigger property but it's not working. Also, I have no binding error and converters are working fine (I only see one StackPanel at the app launch).
Please keep in mind that I don't want to use the code behind part unless there is no other solution.
Thanks for your help.
I finaly gave up and used the code behind part and it's working fine now.
Are your <StackPanel>s part of some UserControl? If not, why are you using DependencyProperty?
Your implementation is quite off as well.
Lets assume for a minute that this is not part of a Custom Control (correct me -- if I'm wrong, I will rewrite the solution)
So you have a ViewModel and you want to hook up some Properties to it. You really don't need to implement DependencyProperty to do what you want to do, but I will entertain you by implementing it your way.
This is a sample ViewModel with 1 (one) property
using Windows.UI.Xaml;
using System.ComponentModel;
// very simple view model
class MyViewModel : DependencyObject, INotifyPropertyChanged
{
// implement INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
// register
public static DependencyProperty FooterTitleProperty = DependencyProperty.Register("FooterTitle", typeof(string), typeof(MyViewModel),
new PropertyMetadata(string.Empty, OnFooterTitlePropertyChanged));
// the actual property
public string FooterTitle
{
get { return (string) GetValue(FooterTitleProperty); }
set
{
SetValue(FooterTitleProperty, value);
}
}
// this will fire when the property gets change
// it will call the OnPropertyChanged to notify the UI element to update its layout
private static void OnFooterTitlePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
{
MyViewModel mvm = dependencyObject as MyViewModel;
mvm.OnPropertyChanged("FooterTitle");
}
}
To test out the code we will make a very simple XAML form
<Grid x:Name="ContentPanel">
<StackPanel>
<TextBlock x:Name="tb" Text="{Binding FooterTitle}" FontSize="48"></TextBlock>
<Button Content="Test Property" Click="Button_Click_1"></Button>
</StackPanel>
</Grid>
When you click on the button we will change the Textbox's Text
public sealed partial class MainPage : Page
{
// create the view model
MyViewModel vm = new MyViewModel();
public MainPage()
{
this.InitializeComponent();
this.NavigationCacheMode = NavigationCacheMode.Required;
// set the text we initial want to display
vm.FooterTitle = "default text";
// set the DataContext of the textbox to the ViewModel
tb.DataContext = vm;
}
// after the button is click we change the TextBox's Text
private void Button_Click_1(object sender, RoutedEventArgs e)
{
// change the text
vm.FooterTitle = "Test Property Has Changed.";
// what happens is the Setter of the Property is called first
// after that happens it launches the `OnFooterTitlePropertyChanged` event
// that we hook up with the Register function.
// `OnFooterTitlePropertyChanged` launches the INotifyPropertyChanged event
// then finally the TextBox will updates it's layout
}
}
At this point you can guess you really don't need the DependencyProperty and say why can't I just launch the INotifyPropertyChanged in the Setter instead? Well you can and it is probably the prefer method.
If all these is part of a UserControl then I can see using a DependencyProperty then in the OnFooterTitlePropertyChanged event you can set the
name_of_textbox.Text = FooterTitle;
I think property name should be given with OnPropertyChanged method, like this;
public bool MyProperty
{
get { return (bool) GetValue(MyPropertyProperty); }
set {
SetValue(MyPropertyProperty, value);
OnPropertyChanged("MyProperty");
}
}
https://learn.microsoft.com/en-us/uwp/api/windows.ui.xaml.data.inotifypropertychanged.propertychanged
How can I bind to content control's content property ?
I'v created custom control :
public class CustomControl
{
// Dependency Properties
public int MyProperty
{
get { return (int)GetValue(MyPropertyProperty); }
set { SetValue(MyPropertyProperty, value); }
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MyPropertyProperty =
DependencyProperty.Register("MyProperty", typeof(int), typeof(MainViewModel), new PropertyMetadata(0));
}
In ViewModel I created a property of type of this custom control :
public CustomControl CustomControl { get; set; }
In view I bind this property to content control :
<ContentControl x:Name="Custom" Content="{Binding CustomControl}"></ContentControl>
Now how can I bind to content control's content property?
<ContentControl Content="{Binding ElementName=Custom, Path=Content}" />
I'm not sure what effect this will have though. I have a suspicion it will complain about UI elements already having a parent or something similar.
Update
If I think I understand your question correctly I don't think you can do what you want using bindings. This is an alternative which adds a callback for when the content is changed so you can set the new content to the property of your VM:
class CustomControl : Control
{
static CustomControl()
{
ContentControl.ContentProperty.OverrideMetadata(typeof(CustomControl), new PropertyMetadata(null, UpdateViewModel));
}
private static void UpdateViewModel(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var control = d as CustomControl;
var viewModel = control.DataContext as MyViewModel;
viewModel.CustomControl = control;
}
}
You'll probably want some error handling in there.