update dialogs sample page

samples/ControlCatalog/Pages/DialogsPage.xaml.cs

@@ -42,13 +42,17 @@ namespace ControlCatalog.Pages
 
             this.FindControl<Button>("OpenFile").Click += async delegate
             {
+                // Almost guaranteed to exist
+                var fullPath = Assembly.GetEntryAssembly()?.GetModules().FirstOrDefault()?.FullyQualifiedName;
+                var initialFileName = fullPath == null ? null : System.IO.Path.GetFileName(fullPath);
+                var initialDirectory = fullPath == null ? null : System.IO.Path.GetDirectoryName(fullPath);
+
                 var result = await new OpenFileDialog()
                 {
                     Title = "Open file",
                     Filters = GetFilters(),
-                    Directory = lastSelectedDirectory,
-                    // Almost guaranteed to exist
-                    InitialFileName = Assembly.GetEntryAssembly()?.GetModules().FirstOrDefault()?.FullyQualifiedName
+                    Directory = initialDirectory,
+                    InitialFileName = initialFileName
                 }.ShowAsync(GetWindow());
                 results.Items = result;
                 resultsVisible.IsVisible = result?.Any() == true;
@@ -84,7 +88,12 @@ namespace ControlCatalog.Pages
                     Title = "Select folder",
                     Directory = lastSelectedDirectory,
                 }.ShowAsync(GetWindow());
-                lastSelectedDirectory = result;
+
+                if (!string.IsNullOrEmpty(result))
+                {
+                    lastSelectedDirectory = result;
+                }
+
                 results.Items = new [] { result };
                 resultsVisible.IsVisible = result != null;
             };