c# - 并发字典 AddOrUpdate 方法第三个参数？

Question

private readonly ConcurrentDictionary<string, System.Drawing.Color> _colorSet;      

public void BuildColorSet(IList<string> colorNames, string prefix, bool forceLastToGray)
{
    var size = forceLastToGray ? colorNames.Count - 1 : colorNames.Count;

    int nbHue = 6;
    int nbCycle = (int)Math.Ceiling((double)size / nbHue);

    var saturationMax = nbCycle <= 2 ? 1.0 : 1.0;
    var saturationMin = 0.3;
    var luminanceMax = nbCycle <= 2 ? 0.85 : 0.85;
    var luminanceMin = 0.3;
    var maxSaturationShift = 0.30;
    var maxLuminanceShift = 0.15;

    var interval = 1.0 / Math.Min(size, nbHue);

    var saturationShift = (saturationMax - saturationMin) / (nbCycle - 1);
    saturationShift = Math.Min(saturationShift, maxSaturationShift);
    var luminanceShift = (luminanceMax - luminanceMin) / (nbCycle - 1);
    luminanceShift = Math.Min(luminanceShift, maxLuminanceShift);

    var hueShift = 0.0;

    var saturation = saturationMax;
    var luminance = luminanceMax;
    for(var i = 0; i<size; i++)
    {
        if(i > 0 && (i % nbHue == 0)) // Next Cycle
        {
            saturation -= saturationShift;
            luminance -= luminanceShift;
            hueShift = hueShift == 0 ? interval/2 : 0;
        }
        var hue = interval*(i%nbHue) + hueShift;

        System.Drawing.Color color = HSL2RGB(hue, saturation, luminance);

    _colorSet.AddOrUpdate(prefix + colorNames[i], color, ???);
    }
    if(forceLastToGray)
    {
        _colorSet.TryAdd(prefix + colorNames[colorNames.Count - 1], System.Drawing.Color.LightGray);
    }

    _cssDirty = true;
}

如果颜色存在新值，我希望能够更新字典。如果字典中没有颜色，也添加到字典中。
我正在使用 AddOrUpdate 但无法获取 AddOrUpdate 方法的第三个参数(形成 lambda 表达式或委托(delegate)方法)。
知道我的第三个参数会是什么样子吗？

Answer 1

来自documentation :

updateValueFactory Type: System.Func The function used to generate a new value for an existing key based on the key's existing value

如果值已经存在，这将单独保留集合中的值:

_colorSet.AddOrUpdate(prefix + colorNames[i], color,
            (key, existingVal) =>
            {
                return existingVal;
            });

这会将集合中的值替换为为插入指定的相同值:

_colorSet.AddOrUpdate(prefix + colorNames[i], color,
            (key, existingVal) =>
            {
                return color;
            });

例如，您可以执行条件逻辑、旧值和新值之间的比较，或更新函数中的原始对象。

_colorSet.AddOrUpdate(prefix + colorNames[i], color,
            (key, existingVal) =>
            {
                if (existingVal.Name == "Red")
                    return existingVal;
                else
                    return color;
            });