Inheritable Dependency Properties

Question

I have an assortment of user controls and I'm trying to see if I can create a base class for them with some dependency properties.

Specifically, most of my user controls follow this format...

<UserControl DataContext="{Binding MyDataContext}" >
    <Expander IsExpanded="{Binding MyExpandedByDefault}">
        <TextBlock>Some text</TextBlock>
    </Expander>
</UserControl>

Of course, normally if this was just a one-off, I'd write the dependency property in the code behind for the above user control. However, since I have multiple user controls that follow the same format, I'd like to put something like the following in a base class...

public bool ExpandedByDefault
{
    get { return (bool)GetValue(ExpandedByDefaultProperty); }
    set { SetValue(ExpandedByDefaultProperty, value); }
}

public static readonly DependencyProperty ExpandedByDefaultProperty =
    DependencyProperty.Register("ExpandedByDefault", typeof(bool), typeof(MyBaseView), new UIPropertyMetadata());

I would like for that to be inherited somewhere so in my main window I can do something like....

<Window>
    <StackPanel>
        <my:Alpha ExpandedByDefault="True" />
        <my:Bravo ExpandedByDefault="False" />
    </StackPanel>
</Window>

Thanks

EDIT:

I have made a base class like so...

public class ViewBase : UserControl
{
    public static readonly DependencyProperty ExpandedByDefaultProperty =
                 DependencyProperty.Register("ExpandedByDefault",
                                             typeof(bool),
                                             typeof(FiapaDbViewerBase),
                                             new FrameworkPropertyMetadata());

    public bool ExpandedByDefault
    {
        get
        {
            return (bool)this.GetValue(ExpandedByDefaultProperty);
        }
        set
        {
            this.SetValue(ExpandedByDefaultProperty, value);
        }
    }
}

But when I try to inherit it in the code behind for my user control like so....

public partial class MyUserControl : ViewBase
{
    public MyUserControl()
    {
        InitializeComponent();
    }
}

I get an error saying

Partial declarations of 'MyUserControl' must not specify different base classes

And I cannot find the other part of the partial class in my solution??? I've tried searching for it in the whole solution...

What is your question? This looks like you already have the answer. — Federico Berasategui, Apr 09 '13 at 15:15

XAMeLi · Accepted Answer · 2013-04-09T15:45:48.077

You can have inheritance. Like so:

Define a base class:

public class BaseExpanderUC : UserControl
{
    public bool ExpandedByDefault
    {
        get { return (bool)GetValue(ExpandedByDefaultProperty); }
        set { SetValue(ExpandedByDefaultProperty, value); }
    }

    public static readonly DependencyProperty ExpandedByDefaultProperty =
        DependencyProperty.Register("ExpandedByDefault", typeof(bool), typeof(MyBaseView), new UIPropertyMetadata(false));
}

Define an inherited classes:

public class Alpha : BaseExpanderUC{}
public class Bravo : BaseExpanderUC{}

In each of the XAMLs of each inherited classes (Alpha and Bravo above), use this makup:

<BaseExpanderUC>
    <Expander IsExpanded="{Binding MyExpandedByDefault,
                                   RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:BaseExpanderUC}}}">
        <TextBlock>Some text</TextBlock>
    </Expander>
</BaseExpanderUC>

Where "local" is an xmlns for the namespace of BaseExpanderUC.

This will demand you to define the UI for each UC. If you can have a common UI for all controls, I'd strongly suggest that you use a custom control (probably inheriting Expander). Then you'll have to define the UI only once, in a ControlTemplate.

Oops, copy-pasted your code, didn't change the root element in XAML. See my edit in clause 3. — XAMeLi, Apr 09 '13 at 15:46
Thanks for your edit... but how does that fix the partial class error I'm getting? Thanks. — imdandman, Apr 09 '13 at 16:29
Derp. Thanks. I missed the part where you Changed the opening tag to ``. I also noticed [this](http://stackoverflow.com/questions/887519/how-can-a-wpf-usercontrol-inherit-a-wpf-usercontrol) previously answered question too in case anyone needs it. — imdandman, Apr 09 '13 at 16:42

Inheritable Dependency Properties

1 Answers1