Option to render trees expanded

[zernyu]

It would be awesome if we could supply an option in the grid constructor to set the default depth of a tree to be expanded when trees are first rendered. The project I am working on has a few requirements that the trees be expanded by default and I have to currently traverse the tree and expand the nodes manually :(

[mikerobi]

I would prefer passing an expandIf function to the column plugin. If the function returns true for a row, the node and and all of its ancestors are rendered expanded.

[zernyu]

+1

That's a much better idea.

[mikerobi]

I realize that in my first comment, I had things backwards. expandIf will only be called when a row is inserted, thus its ancestors have already been expanded.

Determining the depth of a node from within the expandIf function could still require walking up the tree to count nodes. I suggest that it receives the depth as its second argument.

[zernyu]

Or the nodes can have a depth property that the expandIf function can check.

[mikerobi]

If you are using lazy loading, there may be situations where the depth of a record is unknown unless you walk up the tree.

[zernyu]

Doh. I'm an idiot ;)

[ghost]

I've taken a stab at this with #172. Open to comments for the time being.

Thanks @mikerobi for the idea of conditionalizing it. Initially I was very reluctant to entertain the idea of blanket auto-expand, just because I don't like tempting people to use it without considering the consequences (especially if it's being used with a non-memory store, i.e. going back to the server for each request for children).

However, it is a request that comes up fairly often, and this also gave me the opportunity to also allow "preserving" of expanded states when rows get unrendered and re-rendered later (either from scrolling or observer-induced remove/insert operations).

[zernyu]

Awesome, I will test this out now. I've been running into more and more problems with reexpanding trees after refreshing them.

[ghost]

Closing this now, since #172 has been merged. Thanks @swiftdemise for the additional feedback and tire-kicking.