Question

Is it possible to create a custom property and bind it to some value in code behind.

<Style TargetType="{x:Type TreeViewItem}" x:Key="ContainerStyle">
        <Setter Property="IsEditable" Value="{Binding IsEditable, Mode=TwoWay}" />

        <Style.Triggers>
            <Trigger Property="IsEditable" Value="True">
                <Setter Property="HeaderTemplate" Value="{StaticResource EditableTextBox}" />
            </Trigger>

        </Style.Triggers>
    </Style>

What I want to do is swap between the NotEditableText and EditableText templates depending on the value of IsEditable that is set in the PersonViewModel class. But I don’t really how to bind everything together.

SOLUTION

<Style TargetType="{x:Type TreeViewItem}" x:Key="ContainerStyle">
        <Setter Property="ViewModel:PersonViewModel.IsEditable" Value="{Binding IsEditable, Mode=TwoWay}" />

        <Style.Triggers>
            <Trigger Property="ViewModel:PersonViewModel.IsEditable" Value="True">
                <Setter Property="HeaderTemplate" Value="{StaticResource EditableText}" />
            </Trigger>
        </Style.Triggers>

    </Style>

Answer 1

Yes, but your property must be DependancyProperty. Otherwise it will not respond to Binding events. Adding DependancyProperty is quite easy.

public static readonly DependencyProperty IsSpinningProperty = 
    DependencyProperty.Register(
    "IsSpinning", typeof(Boolean),
    );

public bool IsSpinning
{
    get { return (bool)GetValue(IsSpinningProperty); }
    set { SetValue(IsSpinningProperty, value); }
}

Once you create a property like this, you can use it in Style.Triggers as you described in your scenario.
Your property must be present in the class that is used in your TargetType="{x:Type MyType}".