Document reasoning for why CustomMultiChildLayout size can't depend on children and how to do it

[xster]

After reading the CustomMultiChildLayout and associated docs, it's not very clear why it auto-grabs the largest constraint sizes instead of passing the incoming constraints to its delegate and letting the delegate return a size for itself.

It could be a separate widget but still useful to have rather than having a custom render object to avoid all the boilerplate of doing non-layout related things.

cc @matthew-carroll

[xster]

cc @Hixie
Talked about this a few days ago. The reasoning was to not have the delegate implementations also handle various intrinsic sizing functions if the parent's size depended on the children.

[zoechi]

Any suggestion how to deal with that?
I can't even imagine a widget where the size does not depend on it's children.
I don't understand layout well yet though.

[zoechi]

Seems extending RenderBox is the way to go then.

[Hixie]

Yes, if you want to do a custom layout where you define your size based on your children then you just create a render object.

[zoechi]

@Hixie I think it would be a good idea to point that out in the docs where CustomMultiChildLayout says that it can't.

[Hixie]

That's very reasonable!

[estevez-dev]

Could someone please provide an example of extending RenderBox for CustomMultiChildLayout?

[creativecreatorormaybenot]

@estevez-dev https://gist.github.com/jxw1102/a9b58a78a80c8e2f54233b418429fa50

Really, you should just look at RenderStack, i.e. Stack, Column, etc. It is not that complicated.

[creativecreatorormaybenot]

@estevez-dev I actually came across a question on StackOverflow now that was broad enough for me to write a small article about this topic.

Here I explain extensively how to use CustomMultiChildLayout: https://stackoverflow.com/a/59483482/6509751