Binding IsEnabled to the parent ViewModel instead of the UserControl ViewModel

Question

I developed a user control in SilverLight that contains several child controls. Textboxes, ComboBoxes and so on.

The problem is, when I include that UserControl into a parent view and set the complete control to IsEnabled=False, the child controls in that specific UserControl are still enabled.

After all I found the problem.

Adding something like that, implies that the IsEnabled Binding is located in the UserControl binding, not as expected from myself in the DataContext of the parent.

<localControls:TeamEmployeeSelector Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2"
          IsEnabled="{Binding CanModify}" DataContext="{Binding Confidentiality}"/>

QUESTION:
But there's still the question how I can bind the IsEnabled to the ViewModel of the Parent? Because it's not very elegant to copy the CanModify Property to the ViewModel of the Child Control.

Answer 1

Instead of modifying a binding in some way (for example you can make it dependent on other control name as it is proposed in other answer) I would move separate the control which will be disabled and control where DataContext will be changed. For example:

<ContentControl IsEnabled="{Binding CanModify}" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2">
    <localControls:TeamEmployeeSelector DataContext="{Binding Confidentiality}"/>
</ContentControl>

Answer 2

Here is how I would do this.

Your TeamEmployeeSelector UserControl will contain a single root level element which by default is a Grid and is given the name "LayoutRoot".

Now you can bind the IsEnabled property of all the child elements to the UserControl like this:-

 <TextBox IsEnabled="{Binding Parent.IsEnabled, ElementName=LayoutRoot}" ... />

By using element-to-element binding you do not need to copy the CanModify property in to child view models.

Some might suggest that you simply add an x:Name to your UserControl element and then bind directly to it rather than going via the Parent property of the root element as I do above. That'll work ok in Silverlight 4 but not in 3 or WP7. Personally I prefer the above.