fix: do not load whole child collection with virtual scroll (#463)

[Novkirishki]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ X ] The commit message follows our guidelines: https://github.com/CirclonGroup/angular-tree-component/blob/master/CONTRIBUTING.md#commit-message-guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ X ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #463

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ X ] No

Other information

[tobiasengelhardt]

Hi @Novkirishki, thank you for this PR! I tested it so far and it looks good. But I have some trouble reproducing the issue. You said in the issue that it happens when the nodeHeight tree option is INodeHeightFn and not a number. What function are you using and what are you returning?

[Novkirishki]

Hi @tobiasengelhardt, thank you for the quick response! Here is how I reproduce the issue: commit.

The INodeHeightFn function I use simply returns a number. I have added a dummy component to easily track how many instances are created. I have also added a getChildren() function so that the child nodes are loaded async.

When I expand the node with children for the first time I can see in the console that 1000 instances of the dummy component are created. If I collapse the node, further expansions work as expected and only create around 25-6 dummy components, because children height is already calculated and cached. With the fix from the PR there are only 25-6 nodes created on the initial expansion as well.

[tobiasengelhardt]

Very sorry for the late merge. This fix is now included in version 10.0.1. Thank you again for the contribution!