HandyControl | Contains some simple and commonly used WPF controls

I don't believe there is an out-of-the box way to bind to a container index in WPF. Your solution is actually easy to understand.

If you find yourself binding often to index, you could create your own attached property/value converter that internally climbs up the visual tree using these helpers until it finds the parent ItemsControland makes use of the IndexFromContainer method.

Here is some code to get you started with this method:

First a small helper function to climb up the visual tree looking for an item of generic type:

You need to wait until the UserControl has been loaded before calling Window.GetWindow:

I finally solved the problem by locating the problematic HandyControl resource:

Resources have scope. You can merge those just for your control:

Can you create a usable reproduction of the issue please, put it in a github repository, link it here AND create an issue in https://github.com/reactiveui/ReactiveUI/issues

As for questions about "not providing any performance considerations". There are numerous discussions during pull requests about performance and impact (i.e. https://github.com/reactiveui/ReactiveUI/pull/1311 https://github.com/reactiveui/ReactiveUI/pull/1289 and https://github.com/reactiveui/splat/pull/360). In terms of benchmarks, indeed we're short on them, but we have an open issue https://github.com/reactiveui/ReactiveUI/issues/1734 for them. The documentation could be better, there is a lot of knowledge out there on how to get the best out of ReactiveUI, people are welcome to help us improve how to make that knowledge accessible.

As for confidence in a project that has 5000 stars. That 5000 stars is great as an indication of interest, but only interest. The number of people helping to maintain it equates to ~1% with a few people spending their time and passion on a project, some for almost a decade. They want people to be using the project and want to help you get the best out of it. You want confidence in what you are using which is only sensible, but there are companies using it in real-time applications and\or applications used by thousands of users everyday.

I could point you to posts about the NET framework having a magnitude of stars greater than us, and it has perf\knowledge\usability issues as well. But my point will be the maintainers of projects only learn by customers\communities trying things and feeding back.

For your actual problem, there's a team of people who are willing to help. But we need evidence in a reproducible issue, ideally with a test and possibly trace of what you're seeing. We can then assist and understand if you're project is doing something we can help solve, or whether ReactiveUI or the underlying Splat library needs some investigation.