Realtime update feature style

[aleevan2812]

I might need to update a feature’s style at any time in Mapsui v5.
Do you have any suggestions? Thanks!

[pauldendulk]

The best option is to use a ThemeStyle on the ILayer. The constructor of the ThemeStyle gets a Func<IFeature, IStyle?> that can return a style based and the feature.

For performance it is better the limit the total number of style because of caching. So, don't base a color on a float value, but work with a number of different discrete style objects, which you create only once.

[pauldendulk]

You could also implement your own IThemeStyle. Like this:

public class CategorStyle : BaseStyle, IThemeStyle
{
    private readonly IReadOnlyDictionary<string, IStyle> _styles;
    private readonly Func<IFeature, Viewport, string?> _styleKeySelector;

    public CategorStyle(
        IReadOnlyDictionary<string, IStyle> styles,
        Func<IFeature, Viewport, string?> styleKeySelector)
    {
        _styles = styles;
        _styleKeySelector = styleKeySelector;
    }

    public IStyle? GetStyle(IFeature feature, Viewport viewport)
    {
        var key = _styleKeySelector(feature, viewport);
        return key != null && _styles.TryGetValue(key, out var style) ? style : null;
    }
}

Usage:

private static CategorStyle CreateDynamicSvgStyle()
{
    var styles = new Dictionary<string, IStyle>
    {
        ["0"] = new VectorStyle { Fill = new Brush(Color.Red) },
        ["1"] = new VectorStyle { Fill = new Brush(Color.Blue) },
        ["2"] = new VectorStyle { Fill = new Brush(Color.White) }
    };

    var theme = new CategorStyle(styles, (feature, viewport) =>
    {
        var population = (int)(feature.Id % 3);
        return population switch
        {
            < 1 => "0",
            < 2 => "1",
            _ => "2"
        };
    });
    return theme;
}

[aleevan2812]

Actually I want style for cluster feature (not feature),
For example: when a new feature is added then the style of cluster feature in will change color or animations in a few seconds.

[pauldendulk]

Do you have an actual feature that represents a cluster? If not, then how does it work?