Add project files.

UI/WPF/StateTriggerBase.cs

@@ -0,0 +1,16 @@
+using System.Windows;
+
+namespace TheXamlGuy.UI.WPF;
+
+public abstract class StateTriggerBase : DependencyObject
+{
+    internal bool IsTriggerActive { get; private set; }
+
+    internal VisualStateExtension? Owner { get; set; }
+
+    protected void SetActive(bool isActive)
+    {
+        IsTriggerActive = isActive;
+        Owner?.SetActive(IsTriggerActive);
+    }
+}