Use recent language features on Demo Convertors (#3556)

Author: JLdgu

src/MainDemo.Wpf/Converters/BooleanToDoubleConverter.cs

@@ -3,7 +3,7 @@
 
 namespace MaterialDesignDemo.Converters;
 
-public class BooleanToDoubleConverter : MarkupExtension, IValueConverter
+public sealed class BooleanToDoubleConverter : MarkupExtension, IValueConverter
 {
     public double TrueValue { get; set; }
     public double FalseValue { get; set; }
@@ -12,6 +12,5 @@ public class BooleanToDoubleConverter : MarkupExtension, IValueConverter
 
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture) => value is true ? TrueValue : FalseValue;
 
-    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => throw new NotImplementedException();
-    
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => throw new NotImplementedException();    
 }

src/MainDemo.Wpf/Converters/BrushToHexConverter.cs

@@ -9,9 +9,10 @@ public class BrushToHexConverter : IValueConverter
     public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {
         if (value is null) return null;
-        string lowerHexString(int i) => i.ToString("X2").ToLower();
+
+        static string lowerHexString(int i) => i.ToString("X2").ToLower();
         var brush = (SolidColorBrush)value;
-        var hex = lowerHexString(brush.Color.R) +
+        string hex = lowerHexString(brush.Color.R) +
                   lowerHexString(brush.Color.G) +
                   lowerHexString(brush.Color.B);
         return "#" + hex;

src/MainDemo.Wpf/Converters/ColorToBrushConverter.cs

@@ -5,7 +5,7 @@
 namespace MaterialDesignDemo.Converters;
 
 [ValueConversion(typeof(Color), typeof(Brush))]
-public class ColorToBrushConverter : IValueConverter
+public sealed class ColorToBrushConverter : IValueConverter
 {
     public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {

src/MainDemo.Wpf/Converters/IsTransparentConverter.cs

@@ -4,7 +4,7 @@
 
 namespace MaterialDesignDemo.Converters;
 
-public class IsTransparentConverter : IValueConverter
+public sealed class IsTransparentConverter : IValueConverter
 {
     public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {

src/MainDemo.Wpf/Converters/MultiValueEqualityConverter.cs

@@ -3,15 +3,11 @@
 
 namespace MaterialDesignDemo.Converters;
 
-public class MultiValueEqualityConverter : IMultiValueConverter
+public sealed class MultiValueEqualityConverter : IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
-    {
-        return values?.All(o => o?.Equals(values[0]) == true) == true || values?.All(o => o == null) == true;
-    }
+        => values?.All(o => o?.Equals(values[0]) == true) == true || values?.All(o => o == null) == true;
 
     public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
-    {
-        throw new NotImplementedException();
-    }
+        => throw new NotImplementedException();
 }

src/MainDemo.Wpf/Converters/StringJoinConverter.cs

@@ -4,7 +4,7 @@
 
 namespace MaterialDesignDemo.Converters;
 
-public class StringJoinConverter : IValueConverter
+public sealed class StringJoinConverter : IValueConverter
 {
     public string? Separator { get; set; }
 
@@ -15,7 +15,5 @@ public class StringJoinConverter : IValueConverter
     }
 
     public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
-    {
-        throw new NotImplementedException();
-    }
+        => throw new NotImplementedException();
 }