Is it possible to use FStreamableManager for async loading .umap (Map, Level)?
Well i think yes, why not. But how to activate/show this map/world is another story, example of which can be found in FSeamlessTravelHandler i guess.
FStreamableManager is just a manager wrapper for LoadPackageAsync as i understand, for async loading multiple objects/packages at once. Not only packages but also particular assets in packages i suppose ("/Game/PackageName.AssetName") or ("/Game/MyMap").
EDIT1:
Ok, i’ve tested map loading, and it seems working, except one little bug, if i PlayInEditor, then FStreamableManager do not set packages with flag PKG_PlayInEditor, it may lead to crash if you then try to OpenLevel that map, so i have to set it myself after package is loaded, by following code:
if(CurrentWorld->WorldType == EWorldType::PIE)
{
LoadedPackage->GetOutermost()->PackageFlags |= PKG_PlayInEditor;
}
STAFF commentary: