Fix white on white text in DataGrid (#65)

src/MacOS.Avalonia.Theme/Controls/DataGrid.axaml

@@ -102,15 +102,20 @@
     <Setter Property="Background" Value="{DynamicResource TransparentBrush}" />
     <Setter Property="Foreground">
       <Setter.Value>
-        <MultiBinding Converter="{StaticResource BooleanToChoiceConverter}">
-          <MultiBinding Converter="{x:Static BoolConverters.Or}">
-            <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType=DataGridRow}" Path="IsSelected"
-                     Converter="{x:Static BoolConverters.Not}" />
-            <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType=Window}" Path="IsActive"
-                     Converter="{x:Static BoolConverters.Not}" />
+        <MultiBinding Converter="{StaticResource BooleanToChoiceConverter}" ConverterParameter="Foreground White">
+          <MultiBinding Converter="{x:Static BoolConverters.And}">
+            <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType=DataGridRow}" Path="IsSelected" />
+            <MultiBinding Converter="{x:Static BoolConverters.Or}">
+              <MultiBinding Converter="{StaticResource IsUnsetConverter}">
+                <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType=Window}" />
+              </MultiBinding>
+              <MultiBinding Converter="{StaticResource IsExplicitlyTrueConverter}">
+                <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType=Window}" Path="IsActive" />
+              </MultiBinding>
+            </MultiBinding>
           </MultiBinding>
-          <Binding Source="{StaticResource ForegroundHighBrush}" />
           <Binding Source="{StaticResource DataGridForegroundSelectedBrush}" />
+          <Binding Source="{StaticResource ForegroundHighBrush}" />
         </MultiBinding>
       </Setter.Value>
     </Setter>

src/MacOS.Avalonia.Theme/Converters/IsExplicitlyTrueConverter.cs

@@ -0,0 +1,29 @@
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace MacOS.Avalonia.Theme.Converters;
+
+/// <summary>
+///   Takes a _single_ input and returns a boolean based on whether the input is a boolean and true.
+/// </summary>
+/// <param name="value">Any property that may or may not exist</param>
+/// <returns>True if the input resolves to true, else False</returns>
+/// <remarks>
+///   This Converter can be used to check for a property when the source may not even exist. It needs to be a
+///   MultiValueConverter,
+///   because Avalonia will not call a normal converter if the input value is `unset`.
+///   Having this converter is useful, because Avalonia's AND and OR converters will return 'unset' if any of the inputs
+///   are unset, even when one of the inputs is a boolean and would be sufficient to verify the conjunction!
+/// </remarks>
+public class IsExplicitlyTrueConverter : IMultiValueConverter
+{
+  public object Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+  {
+    return values[0] is true;
+  }
+
+  public object ConvertBack(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+  {
+    throw new NotImplementedException();
+  }
+}

src/MacOS.Avalonia.Theme/Converters/IsUnsetConverter.cs

@@ -0,0 +1,29 @@
+using System.Globalization;
+using Avalonia;
+using Avalonia.Data.Converters;
+
+namespace MacOS.Avalonia.Theme.Converters;
+
+/// <summary>
+///   Takes a _single_ input and returns a boolean if it is unset.
+/// </summary>
+/// <param name="value">Any property or property source that may or may not exist</param>
+/// <returns>True if the input resolves to AvaloniaProperty.UnsetValue, else False</returns>
+/// <remarks>
+///   This Converter can be used to check for the presence of a control or property. It needs to be a MultiValueConverter,
+///   because Avalonia will not call a normal converter if the input value is `unset`.
+///   Having this converter is useful, because Avalonia's AND and OR converters will return 'unset' if any of the inputs
+///   are unset, even when one of the inputs is a boolean and would be sufficient to verify the conjunction!
+/// </remarks>
+public class IsUnsetConverter : IMultiValueConverter
+{
+  public object Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+  {
+    return values[0] == AvaloniaProperty.UnsetValue;
+  }
+
+  public object ConvertBack(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+  {
+    throw new NotImplementedException();
+  }
+}

src/MacOS.Avalonia.Theme/Converters/_index.axaml

@@ -7,6 +7,8 @@
   <converters:CharToMacOsPasswordCharConverter x:Key="CharToMacOsPasswordCharConverter" />
   <converters:RevealPasswordToFontSizeConverter x:Key="RevealPasswordToFontSizeConverter" />
   <converters:BooleanToChoiceConverter x:Key="BooleanToChoiceConverter" />
+  <converters:IsUnsetConverter x:Key="IsUnsetConverter" />
+  <converters:IsExplicitlyTrueConverter x:Key="IsExplicitlyTrueConverter" />
   <converters:ClassToChoiceConverter x:Key="ClassToChoiceConverter" />
   <converters:ColorToCssFillConverter x:Key="ColorToCssFillConverter" />
   <converters:ThicknessToSelectiveThicknessConverter x:Key="ThicknessToSelectiveThicknessConverter" />