具有依赖于复选框值的可为空依赖属性的 WPF UserControl

Question

I'm trying to create a custom UserControl that displays the properties of a complex object as a form. Additionally, if the user unchecks a checkbox in the header of the UserControl, the value of the dependency property should be null (but the form values should stay displayed, even if the form is disabled) - and vice versa.

I'm working with two dependency properties of type ComplexObject on the UserControl - one is public (this will be bound to by the client), another is private (its properties will be bound to the internal controls in the UserControl):

    public ComplexObject ComplexObject 
    {
        get { return (ComplexObject )GetValue(ComplexObjectProperty); }
        set { SetValue(ComplexObjectProperty, value); }
    }

    private ComplexObject VisibleComplexObject 
    {
        get { return (ComplexObject)GetValue(VisibleComplexObjectProperty); }
        set { SetValue(VisibleComplexObjectProperty, value); }
    }

Now I'm struggling with a binding between those two, so that CompexObject becomes either VisibleComplexObject or null based on the checkbox value. This should also work the other way. I've tried to solve this using DataTriggers in the Style of the UserControl, but was unable to do so:

<UserControl.Style>
    <Style TargetType="local:CheckableComplexTypeGroup">
        // 'CheckableComplexTypeGroup' TargetType does not match type of the element 'UserControl'
    </Style>
</UserControl.Style> 

Using <local:CheckableComplexTypeGroup.Style> instead of <UserControl.Style> didn't work either.

Are there any other suggestions? Or maybe another way of doing this?

Answer 1

Finally I've solved this without using plain old event handlers instead of binding/triggers.

CheckableComplexObjectGroup.xaml:

<UserControl Name="thisUC" ...>
  <GroupBox>
    <GroupBox.Header>
        <CheckBox Name="cbComplexObject" 
                  IsChecked="{Binding ElementName=thisUC, Path=ComplexObject, Mode=OneWay, Converter={StaticResource nullToFalseConv}}"
                  Checked="cbComplexObject_Checked" Unchecked="cbComplexObject_Unchecked"/>
    </GroupBox.Header>
    ...
</UserControl>

CheckableComplexObjectGroup.cs:

public static readonly DependencyProperty ComplexObjectProperty =
        DependencyProperty.Register("ComplexObject", 
                                    typeof(ComplexObject), 
                                    typeof(CheckableComplexObjectGroup), 
                                    new PropertyMetadata(null));
private static readonly DependencyProperty VisibleComplexObjectProperty =
        DependencyProperty.Register("VisibleComplexObject", 
                                    typeof(ComplexObject), 
                                    typeof(CheckableComplexObjectGroup), 
                                    new PropertyMetadata(new ComplexObject()));

//...

protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
{
    if (e.Property == ComplexObjectProperty)
    {
        if (null != e.NewValue)
            VisibleComplexObject = ComplexObject;
    }

    base.OnPropertyChanged(e);
}

private void cbComplexObject_Checked(object sender, RoutedEventArgs e)
{
    ComplexObject = VisibleComplexObject;
}

private void cbComplexObject_Unchecked(object sender, RoutedEventArgs e)
{
    ComplexObject = null;
}