Add project files.

Helpers/EnumToBooleanConverter.cs

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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.
+
+using System.Globalization;
+using System.Windows.Data;
+using Wpf.Ui.Appearance;
+
+namespace DownloadManager.Helpers;
+internal class EnumToBooleanConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+    {
+        if (parameter is not String enumString)
+        {
+            throw new ArgumentException("ExceptionEnumToBooleanConverterParameterMustBeAnEnumName");
+        }
+
+        if (!Enum.IsDefined(typeof(ApplicationTheme), value))
+        {
+            throw new ArgumentException("ExceptionEnumToBooleanConverterValueMustBeAnEnum");
+        }
+
+        var enumValue = Enum.Parse(typeof(ApplicationTheme), enumString);
+
+        return enumValue.Equals(value);
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+    {
+        if (parameter is not String enumString)
+        {
+            throw new ArgumentException("ExceptionEnumToBooleanConverterParameterMustBeAnEnumName");
+        }
+
+        return Enum.Parse(typeof(ApplicationTheme), enumString);
+    }
+}