❔ WPF Converter Infinite call

public class RelativeFontSizeConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        try {
            double baseSize;
            bool validBaseSize = IsDouble(value, out baseSize);

            if (!validBaseSize || !IsValidNumber(baseSize)) {
                throw new ArgumentException("value must be a double", nameof(value));
            }

            if (Ratio is not null) {
                return baseSize * Ratio;
            }

            double ratio;
            bool validRatio = IsDouble(parameter, out ratio);
            if (!validRatio || !IsValidNumber(ratio)) {
                throw new ArgumentException("parameter must be a double", nameof(parameter));
            }

            return baseSize * ratio;
        }
        catch {
            if (WhenInvalid is not null) {
                return WhenInvalid.Value;
            }

            throw;
        }

    }

    private static bool IsDouble(object s, out double value) {
        if (s is double d) {
            value = d;
            return true;
        }

        return double.TryParse(s.ToString(), NumberStyles.Any, NumberFormatInfo.InvariantInfo, out value);
    }

    private bool IsValidNumber(double num) {
        return !double.IsNaN(num) && !double.IsInfinity(num) && num > 0;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
        throw new NotImplementedException();
    }

    // allows the converter to be used for different font ratios
    public double? Ratio { get; set; }

    //When result is zero, null or negative
    public double? WhenInvalid { get; set; }
}

public class RelativeFontSizeConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        try {
            double baseSize;
            bool validBaseSize = IsDouble(value, out baseSize);

            if (!validBaseSize || !IsValidNumber(baseSize)) {
                throw new ArgumentException("value must be a double", nameof(value));
            }

            if (Ratio is not null) {
                return baseSize * Ratio;
            }

            double ratio;
            bool validRatio = IsDouble(parameter, out ratio);
            if (!validRatio || !IsValidNumber(ratio)) {
                throw new ArgumentException("parameter must be a double", nameof(parameter));
            }

            return baseSize * ratio;
        }
        catch {
            if (WhenInvalid is not null) {
                return WhenInvalid.Value;
            }

            throw;
        }

    }

    private static bool IsDouble(object s, out double value) {
        if (s is double d) {
            value = d;
            return true;
        }

        return double.TryParse(s.ToString(), NumberStyles.Any, NumberFormatInfo.InvariantInfo, out value);
    }

    private bool IsValidNumber(double num) {
        return !double.IsNaN(num) && !double.IsInfinity(num) && num > 0;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
        throw new NotImplementedException();
    }

    // allows the converter to be used for different font ratios
    public double? Ratio { get; set; }

    //When result is zero, null or negative
    public double? WhenInvalid { get; set; }
}

        <Viewbox
            Grid.Column="0"
            StretchDirection="DownOnly">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition />
                    <RowDefinition />
                </Grid.RowDefinitions>

                <TextBlock
                    Grid.Row="0"
                    Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Viewbox}}"
                    d:Text="Tell Mark about project's current milestones to be met and hit"
                    FontWeight="SemiBold"
                    Foreground="{StaticResource BrushFgDefault}"
                    Text="{Binding Todo.Title}"
                    TextTrimming="CharacterEllipsis" />

                <TextBlock
                    Grid.Row="1"
                    Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Viewbox}}"
                    d:Text="Tell Mark the details of the project that he has been recently included in as such that he knows the plan"
                    Foreground="{StaticResource BrushFgMuted}"
                    Text="{Binding Todo.Description}"
                    TextWrapping="Wrap" />
            </Grid>

        </Viewbox>

        <Viewbox
            Grid.Column="0"
            StretchDirection="DownOnly">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition />
                    <RowDefinition />
                </Grid.RowDefinitions>

                <TextBlock
                    Grid.Row="0"
                    Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Viewbox}}"
                    d:Text="Tell Mark about project's current milestones to be met and hit"
                    FontWeight="SemiBold"
                    Foreground="{StaticResource BrushFgDefault}"
                    Text="{Binding Todo.Title}"
                    TextTrimming="CharacterEllipsis" />

                <TextBlock
                    Grid.Row="1"
                    Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Viewbox}}"
                    d:Text="Tell Mark the details of the project that he has been recently included in as such that he knows the plan"
                    Foreground="{StaticResource BrushFgMuted}"
                    Text="{Binding Todo.Description}"
                    TextWrapping="Wrap" />
            </Grid>

        </Viewbox>