How do I bind to RelativeSource Self?

Question

I am trying to bind several different properties in my Xaml:

<Label Content="{Binding Description}" Visibility="{Binding Path=DescriptionVisibility, ElementName=_UserInputOutput}" FontSize="{Binding Path=FontSizeValue, ElementName=_UserInputOutput}" HorizontalAlignment="Left" VerticalAlignment="Top" Padding="0" />

You will noticed I have used two Different binding techniques here. The ones using Element Name work, the other does not. Here is code behind:

public string Description { get { return (string)GetValue(DescriptionProperty); } set { SetValue(DescriptionProperty, value); } } public static readonly DependencyProperty DescriptionProperty = DependencyProperty.Register("Description", typeof(string), typeof(UserControl), new UIPropertyMetadata(""));

Each Binding has a different name but they all look like this for the most part. I want my Binding to be able to work with:

{Binding Description}

Instead of:

{Binding Path=Description, ElementName=_UserInputOutput}

It only seems to be working when ElementName is used. I need to export/import this XAML, so I can't have a ElementName or the import won't work.

I thought this would be best:

{Binding Path=Description, RelativeSource={RelativeSource Self}}

This did not work.

Any ideas?? Thank you!

This article might be of interest.

brunnerh
– brunnerh

2012-08-16 23:01:50 +00:00
Commented Aug 16, 2012 at 23:01 — brunnerh
– brunnerh, Commented Aug 16, 2012 at 23:01

Community · Accepted Answer · 2017-05-23 11:33:25Z

{RelativeSource Self} targets the object that owns the property that is being bound, if you have such a binding on a Label it will look for Label.Description, which isn't there. Instead you should use {RelativeSource AncestorType=UserControl}.

Bindings without a source (ElementName, Source, RelativeSource) are relative to the DataContext, however in UserControls you should avoid setting the DataContext to not mess with external bindings.

Douglas · Accepted Answer · 2013-12-09 10:46:43Z

38

You haven't set the DataContext, which is what the RelativeSource is using to determine what it's relative to. You need to set the DataContext at a higher level, like the UserControl. I typically have:

<UserControl ... DataContext="{Binding RelativeSource={RelativeSource Self}}"> </UserControl>

This tells the UserControl to bind itself the class in the codebehind.

edited Dec 9, 2013 at 10:46

Douglas

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answered Aug 16, 2012 at 21:09

Joel Lucsy

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4 Comments

brunnerh Over a year ago

"which is what the RelativeSource is using to determine what it's relative to" That statement is plain incorrect. Also setting the DataContext of a UserControl is rarely a good idea...

codingdave Over a year ago

I think this is not a good idea since it violates the MVVM paradigm: When we want to use WPF with MVVM we have a View that binds to its ViewModel. So inside the constructor of the code behind of the View we say View() { InitializeComponent(); DataContext = new ViewModel(); } This makes all data binding operations work on the ViewModel so we can separate the view from the ViewModel.

ToolmakerSteve Over a year ago

Its unlikely that you want (or even need) to do what is suggested here. The upvotes seem ill-advised.

TJ Bandrowsky Over a year ago

@codingdave I agree except there's some thinking that you can simplify using your controls in a hierarchy if you either let the parent set the view model or use binding to bind the dependency.

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