优化更新代码，添加界面功能并整合

WPFluent/Controls/LoadingScreen/LoadingScreen.cs

@@ -0,0 +1,12 @@
+
+
+
+// ReSharper disable once CheckNamespace
+namespace WPFluent.Controls;
+
+/// <summary>
+/// Prestyled loading screen with <see cref="ProgressRing"/>.
+/// </summary>
+public class LoadingScreen : System.Windows.Controls.ContentControl
+{
+}

WPFluent/Controls/LoadingScreen/LoadingScreen.xaml

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+<!--
+    This Source Code Form is subject to the terms of the MIT License.
+    If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+    Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+    All Rights Reserved.
+-->
+
+<ResourceDictionary
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:controls="clr-namespace:WPFluent.Controls">
+
+    <Style TargetType="{x:Type controls:LoadingScreen}">
+        <Setter Property="Background" Value="{DynamicResource LoadingScreenForeground}" />
+        <Setter Property="Background" Value="{DynamicResource LoadingScreenBackground}" />
+        <Setter Property="SnapsToDevicePixels" Value="True" />
+        <Setter Property="OverridesDefaultStyle" Value="True" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="{x:Type controls:LoadingScreen}">
+                    <Grid
+                        Width="{TemplateBinding Width}"
+                        Height="{TemplateBinding Height}"
+                        Background="{TemplateBinding Background}">
+                        <Grid.ColumnDefinitions>
+                            <ColumnDefinition Width="*" />
+                            <ColumnDefinition Width="*" />
+                        </Grid.ColumnDefinitions>
+
+                        <Grid Grid.Column="0" VerticalAlignment="Center">
+                            <controls:ProgressRing IsIndeterminate="True" />
+                        </Grid>
+
+                        <Grid Grid.Column="1" VerticalAlignment="Center">
+                            <ContentPresenter />
+                        </Grid>
+                    </Grid>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+</ResourceDictionary>