Binding Visibility to DataContext

Question

I have a value converter that converts null to Visibility.Collapsed. Now I try to use it in a user control so that the whole control would collapse when it's DateContext is null

The control looks like this:

<UserControl x:Class="PhoneApp.Controls.Header"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Visibility="{Binding Converter={StaticResource ToVisibility}}"
    d:DesignHeight="150" d:DesignWidth="480"> <-- some body here -->

And it is used like this

<my:Header DataContext="{Binding SectionHeader}"/>

Where SectionHeader is a view model property.

I hava a similar control where I don't bind DataContext but some custom DP and the collapsing there works fine. However, in this one, the value converter seems to be called only when the SectionHeader != null. When it is null, the control is rendered with empty children.

I thought about not using DataContext here but the control is much cleaner with it.

Why binding to DataContext doesn't work? What do you suggest?

Answer 1

In this case, when DataContext is null, binding will use value specified in TargetNullValue property. So simply set TargetNullValue=Collapsed and you're good to go :

Visibility="{Binding TargetNullValue=Collapsed}"

Reference : [How to Set TargetNullValue to Visibility.Collapsed in Binding]