Make converter classes sealed and simplify null checks

All converter classes are now sealed to prevent inheritance, improving clarity and potential performance. Null checks in Percent100 converters are simplified using the null-coalescing assignment operator.

Author: emako

QuickLook.Plugin/QuickLook.Plugin.ArchiveViewer/Converters.cs

@@ -23,12 +23,11 @@
 
 namespace QuickLook.Plugin.ArchiveViewer;
 
-public class Percent100ToVisibilityVisibleConverter : DependencyObject, IValueConverter
+public sealed class Percent100ToVisibilityVisibleConverter : DependencyObject, IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
     {
-        if (value == null)
-            value = 0;
+        value ??= 0;
 
         var percent = (double)value;
         return Math.Abs(percent - 100) < 0.00001 ? Visibility.Visible : Visibility.Collapsed;
@@ -40,12 +39,11 @@ public object ConvertBack(object value, Type targetTypes, object parameter, Cult
     }
 }
 
-public class Percent100ToVisibilityCollapsedConverter : DependencyObject, IValueConverter
+public sealed class Percent100ToVisibilityCollapsedConverter : DependencyObject, IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
     {
-        if (value == null)
-            value = 0;
+        value ??= 0;
 
         var percent = (double)value;
         return Math.Abs(percent - 100) < 0.00001 ? Visibility.Collapsed : Visibility.Visible;
@@ -57,7 +55,7 @@ public object ConvertBack(object value, Type targetTypes, object parameter, Cult
     }
 }
 
-public class LevelToIndentConverter : DependencyObject, IMultiValueConverter
+public sealed class LevelToIndentConverter : DependencyObject, IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {
@@ -75,7 +73,7 @@ public object[] ConvertBack(object value, Type[] targetTypes, object parameter,
     }
 }
 
-public class LevelToBooleanConverter : DependencyObject, IValueConverter
+public sealed class LevelToBooleanConverter : DependencyObject, IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
     {
@@ -90,7 +88,7 @@ public object ConvertBack(object value, Type targetType, object parameter, Cultu
     }
 }
 
-public class BooleanToAsteriskConverter : DependencyObject, IValueConverter
+public sealed class BooleanToAsteriskConverter : DependencyObject, IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
     {
@@ -105,7 +103,7 @@ public object ConvertBack(object value, Type targetType, object parameter, Cultu
     }
 }
 
-public class SizePrettyPrintConverter : DependencyObject, IMultiValueConverter
+public sealed class SizePrettyPrintConverter : DependencyObject, IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {
@@ -121,7 +119,7 @@ public object[] ConvertBack(object value, Type[] targetTypes, object parameter,
     }
 }
 
-public class DatePrintConverter : DependencyObject, IMultiValueConverter
+public sealed class DatePrintConverter : DependencyObject, IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {
@@ -137,7 +135,7 @@ public object[] ConvertBack(object value, Type[] targetTypes, object parameter,
     }
 }
 
-public class FileExtToIconConverter : DependencyObject, IMultiValueConverter
+public sealed class FileExtToIconConverter : DependencyObject, IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {