Binding property to Silverlight dependency property independent of DataContext

Question

I'm trying to make an Address control that has an IsReadOnly property, which will make every TextBox inside read only when set to true.

 <my:AddressControl Grid.Column="1" Margin="5" IsReadOnly="True"/>

I've managed to do this just fine with a dependency property and it works.

Here's a simple class with the dependency property declared :

public partial class AddressControl : UserControl
{
    public AddressControl()
    {
        InitializeComponent();
        this.DataContext = this;
    }

    public static readonly DependencyProperty IsReadOnlyProperty = 
       DependencyProperty.Register("IsReadOnly", typeof(bool), 
                                   typeof(AddressControl), null);

    public bool IsReadOnly
    {
        get { return (bool)GetValue(IsReadOnlyProperty); }
        set { SetValue(IsReadOnlyProperty, value); }
    }
}

In the XAML for this codebehind file I have a Textbox for each address line:

  <TextBox IsReadOnly="{Binding IsReadOnly}" Text="{Binding City, Mode=TwoWay}"/>
  <TextBox IsReadOnly="{Binding IsReadOnly}" Text="{Binding State, Mode=TwoWay}"/>
  <TextBox IsReadOnly="{Binding IsReadOnly}" Text="{Binding Zip, Mode=TwoWay}"/>

Like i said this works just fine. The problem is that the Address control itself is bound to its parent object (I have several addresses I am binding).

 <my:AddressControl DataContext="{Binding ShippingAddress, Mode=TwoWay}" IsReadOnly="True">
 <my:AddressControl DataContext="{Binding BillingAddress, Mode=TwoWay}" IsReadOnly="True">

The problem is that as soon as I set DataContext to something other than 'this' then the binding for IsReadOnly breaks. Not surprising because its looking for IsReadOnly on the Address data entity and it doesn't exist or belong there.

I've tried just about every combination of binding attributes to get IsReadOnly to bind to the AddressControl obejct but can't get it working.

I've tried things like this, but I can't get IsReadOnly to bind independently to the AddressControl property instead of its DataContext.

<TextBox IsReadOnly="{Binding RelativeSource={RelativeSource Self}, Path=IsReadOnlyProperty}" Text="{Binding City, Mode=TwoWay}" />

I think I'm pretty close. What am I doing wrong?

Answer 1

I think you're stuck, at least, if you want to do this just via binding. My guess is that you're going to have to resort to code-behind, presumably by iterating through your child textbox controls and setting their IsReadOnly propert as a side-effect of your Address control's IsReadOnly property.

Unlike some folks who think that any code sitting in a code-behind file is effectively an admission of failure, I don't get religious about it: if throwing some code into a code-behind is the easiest way to do something, that's where I put my code. On the contrary, if I have to spend half a day trying to figure out how to do something via binding that I could do in five minutes with a code-behind, that's failure, IMO.

Answer 2

With this answer (actually my own answer to a similar question) I have a good [better] solution.

I still have to iterate through the textboxes, but I don't have to set the actual value. I can create bindings in the codebehind - just not with XAML.