How can I style a DataGridCell's content based on binding without naming that binding

Question

I would like to create a style that makes my cell's content green if positive, red if negative or black if 0.

I know about converters and bindings, but is it possible to do this without naming the field the specific column is bound to (eg. I was to base on whatever is the cell's value)?

            <Style x:Key="GreenIfPositive" TargetType="DataGridCell" BasedOn="{StaticResource {x:Type DataGridCell}}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding, Converter={StaticResource greaterThanZeroDecimalConverter}}" Value="True">
                        <Setter Property="Foreground" Value="Green"/>
                    </DataTrigger>
                    <DataTrigger BBinding="{Binding, Converter={StaticResource greaterThanZeroDecimalConverter}}" Value="False">
                        <Setter Property="Foreground" Value="Red"/>
                    </DataTrigger>
                    <DataTrigger Binding="{Binding}" Value="0">
                        <Setter Property="Foreground" Value="Black"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>

So that I could use it on columns without re-iterating that style just so I can select the property I'm basing this on.

Answer 1

here is a solution for DataGridTextColumns. DataGridTextColumn creates TextBlock element to display cell value. TextBlock has string Text property. Those TextBlocks can be accessed via DataGridCell Content property, so resulting binding path is "Content.Text"

<Style.Triggers>
    <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, 
                 Path=Content.Text, Mode=OneWay,
                 Converter={StaticResource greaterThanZeroDecimalConverter}}" 
                 Value="True">
        <Setter Property="Foreground" Value="Green"/>
    </DataTrigger>
    <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, 
                 Path=Content.Text, Mode=OneWay,
                 Converter={StaticResource greaterThanZeroDecimalConverter}}" 
                 Value="False">
        <Setter Property="Foreground" Value="Red"/>
    </DataTrigger>
    <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, 
                 Path=Content.Text, Mode=OneWay}" 
                 Value="0">
        <Setter Property="Foreground" Value="Black"/>
    </DataTrigger>
</Style.Triggers>

note {RelativeSource Self}.

I also had to change Convert method because Text is a string property and incoming value is string.

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    double d;
    if (value != null && value is string && double.TryParse(value.ToString(), out d))
    {
        return d > 0;
    }
    return null;
}