Hello @AiMiDi,
it would really help if you could clarify/confirm the context. I am still assuming that you are writing a SceneLoaderData, namely for your MikuMikuDance project.
We have an example on GitHub for how to implement an im- and exporter plugin, the STL-example. Invoking the status bar indicators, i.e., StatusSetSpin. StatusSetBar and StatusSetText, for a computational process, e.g., loading a file, are a bit of a special case regarding the UI-restrictions. I always also struggle with them and what is allowed where. In general, you can get away with a bit more with them, as they do not check immediately for being on the main thread and do not refuse execution if they are not. But you can also run into problems with them outside of the main thread. With that being said, our STL example also makes use of StatusSetBar, which sort of indicates that it is safe to use within SceneLoaderData::Load (more on that later).
Regarding providing a custom progress dialogs for the import process: Most importers of Cinema do not do that. There are exceptions like the FBX importer which spawns its own dialog to give feedback for the importing process.
When you invoke GeIsMainThread() in SceneLoaderData::Load, you will see that you are in almost all cases in the main thread (at least the ones where I did try). But in the end, there is no guarantee that this will always hold true. What I would do is safeguard all GUI operations with GeIsMainThread(), including status-bar operations, i.e., only carry them out when Load is being called from the main thread and otherwise just skip them. Then you can also open as many dialogs as you want from there.
Our FBX importer plugin for example instantiates an interface for handling importing FBX within Load. Cascading out from that interfac instantiation, also a ProgressDialog will be being instantiated and opened (there are some types involved in between). But frankly, I would not bother with all that complexity and just use the status bar of the main app, i.e., StatusSetBar. Checking for the main thread seems advisable though.
Cheers,
Ferdinand
