Make TriggerCollection Constructor Public

Is your feature request related to a problem? Please describe. I was looking at a use case where I wanted multiple triggers to fire the same action. I could have repeated the action for every trigger, but it smells bad. I had a hard time writing a solution because the access modifiers for various structures are limited. My solution was a "MultiTrigger" implementation that utilizes a TriggerCollection, but due to its accessibility, I had to had it together using the Interaction.GetTriggers method (see additional context).

Describe the solution you'd like TriggerCollection is general enough that it could have a public constructor.
https://github.com/microsoft/XamlBehaviorsWpf/blob/master/src/Microsoft.Xaml.Behaviors/TriggerCollection.cs#L17

The only usage of the class is in Interaction and that is locked down to prevent a TriggerCollection from overwriting an existing TriggerCollection on the TriggersProperty. https://github.com/microsoft/XamlBehaviorsWpf/blob/master/src/Microsoft.Xaml.Behaviors/Interaction.cs#L36 https://github.com/microsoft/XamlBehaviorsWpf/blob/master/src/Microsoft.Xaml.Behaviors/Interaction.cs#L62

While its understandable that future changes could break the TriggerCollection and leaving it as internal could prevent a breaking change, I think this risk is warranted.

Describe alternatives you've considered

Writing my own TriggerCollection implementation. It would essentially amount to a copy paste of existing code and thereby smells bad.
Having XamlBehaviorsWpf implement a MultiTrigger (this may be preferable to control breaking changes)

Additional context Here is my MultiTrigger implementation. I have my reasons for using Return/Tab instead of a DataTrigger and I believe that conversation is moot to the general problem of a multitrigger. XAML:

        xmlns:CoreBehaviors="clr-namespace:MyCode.Core.Behaviors"
...
                <TextBox 
                    x:Name="tbLookup">
                    <b:Interaction.Triggers>
                        <CoreBehaviors:MultiTrigger>
                            <CoreBehaviors:MultiTrigger.Triggers>
                                <b:KeyTrigger Key="Return" />
                                <b:KeyTrigger Key="Tab" />
                            </CoreBehaviors:MultiTrigger.Triggers>

                            <b:InvokeCommandAction Command="{Binding LookupCommand}" CommandParameter="{Binding Text, ElementName=tbLookup}" />
                        </CoreBehaviors:MultiTrigger>
                    </b:Interaction.Triggers>
                </TextBox>

MultiTrigger.cs:

using Microsoft.Xaml.Behaviors;
using System.Collections.Specialized;
using System.Linq;
using System.Windows;
using TriggerBase = Microsoft.Xaml.Behaviors.TriggerBase;

namespace MyCode.Core.Behaviors
{
    public class MultiTrigger : TriggerBase<DependencyObject>
    {
        public MultiTrigger()
        {
            Triggers = Interaction.GetTriggers(this); //HACK: use GetTriggers to "construct" TriggerCollection
            Triggers.Detach();  //HACK: We need to immediately detach the associated object (this) so we can attach it to this instances associated object in OnAttached
            ((INotifyCollectionChanged)Triggers).CollectionChanged += MultiTrigger_CollectionChanged;
        }

        public Microsoft.Xaml.Behaviors.TriggerCollection Triggers { get; }

        private void MultiTrigger_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e.OldItems != null)
                foreach (TriggerBase item in e.OldItems.Cast<TriggerBase>())
                    foreach(MultiTriggerActionAdapter? action in item.Actions.OfType<MultiTriggerActionAdapter>())
                        item.Actions.Remove(action);

            if (e.NewItems != null)
                foreach (TriggerBase item in e.NewItems.Cast<TriggerBase>())
                    item.Actions.Add(new MultiTriggerActionAdapter(this));
        }

        protected override void OnAttached()
        {
            Triggers.Attach(AssociatedObject);
            base.OnAttached();
        }

        protected override void OnDetaching()
        {
            Triggers.Detach();
            base.OnDetaching();
        }

        private class MultiTriggerActionAdapter : TriggerAction<DependencyObject>
        {
            private readonly MultiTrigger _parent;

            public MultiTriggerActionAdapter(MultiTrigger parent)
            {
                _parent = parent;
            }
            protected override void Invoke(object parameter)
                => _parent.InvokeActions(parameter);
        }
    }
}

microsoft / XamlBehaviorsWpf

Make TriggerCollection Constructor Public #103