优化更新代码，添加界面功能并整合

WPFluent/Extensions/FrameExtensions.cs

@@ -0,0 +1,32 @@
+
+
+
+using System.Windows.Controls;
+
+namespace WPFluent.Extensions;
+
+/// <summary>
+/// Set of extensions for <see cref="System.Windows.Controls.Frame"/>.
+/// </summary>
+public static class FrameExtensions
+{
+    /// <summary>
+    /// Cleans <see cref="Frame"/> journal.
+    /// </summary>
+    /// <param name="frame">Selected frame.</param>
+    public static void CleanNavigation(this Frame frame)
+    {
+        while(frame.CanGoBack)
+        {
+            _ = frame.RemoveBackEntry();
+        }
+    }
+
+    /// <summary>
+    /// Gets <see cref="FrameworkElement.DataContext"/> from <see cref="Frame"/>.
+    /// </summary>
+    /// <param name="frame">Selected frame.</param>
+    /// <returns>DataContext of currently active element, otherwise <see langword="null"/>.</returns>
+    public static object? GetDataContext(this Frame frame)
+    { return frame.Content is not FrameworkElement element ? null : element.DataContext; }
+}