How to create nested XElement based on a condition?

I am trying to create save a data structure as xml like so:

return new XElement ( "EffectFile",
    new XElement ( "Effects", this.Effects.Select ( e => new XElement ( "Effect", e.EffectType ) ) )
).ToString ( );

which creates something like this:

开发者_高级运维<EffectFile>
  <Effects>
    <Effect>Blur</Effect>
    <Effect>Sharpen</Effect>
    <Effect>Median</Effect>
  </Effects>
</EffectFile>

But I also want to have a condition that if an effect has opacity, I want to save that too within the effect.

I just can't workout how to nest that condition inside the lambda expression to create a nested XElement.

EDIT: So for Opacity, let's say it's something like this:

if (e.Opacity != null) new xElement("Opacity", e.Opacity)

---

It is better for you to store your file like that:

<EffectFile>
  <Effects>
    <Effect>
       <EffectType>Blur</EffectType>
       <Opacity>100</Opacity>
    </Effect>
  </Effects>
</EffectFile>

_

 return new XElement("EffectFile",
                                    new XElement("Effects", this.Effects.Select(e => new XElement("Effect", new XElement("EffectType", e.EffectType), e.Opacity != null ? new XElement("Opacity", e.Opacity) : null)))
                    ).ToString();

---

Assuming Opacity is a float instance property on your class, you could combine the ternary operator (?:) with the Concat extension method.

return new XElement("EffectFile",
    new XElement("Effects",
        this.Effects
            .Select(e => new XElement("Effect", e.EffectType))
            .Concat(this.Opacity > 0.0f
                ? new[] { new XElement("Opacity", this.Opacity) }
                : Enumerable.Empty<XElement>()
                )
        )
    )
    .ToString();

Translation of my additions:

If opacity is greater than zero, make a new list of size 1 (with an Opacity element), and append that to the effects list. If opacity is less than or equal to zero, make a new list of size zero, and append that to the effects list (basically a no-op, as far as the list goes).

Your output file will look like the one you specified in your question if the opacity is <= 0, and should look like this if it is > 0:

<EffectFile>
  <Effects>
    <Effect>Blur</Effect>
    <Effect>Sharpen</Effect>
    <Effect>Median</Effect>
    <Opacity>0.75</Opacity>
  </Effects>
</EffectFile>

Edit:

To match your new specifications, simply change this.Opacity > 0.0f to this.Opacity != null, and make sure you have the appropriate ToString method defined for Opacity. The resulting XML will end up looking more-or-less the same.