I trackedentity an entity, I take some time to track, so I want to add a loading

[fruit...@outlook.com]

1. A concise explanation of the problem you're experiencing.

I trackedentity an entity, I take some time to track, so I want to add a loading,how to know loading success

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

[Omar Shehata]

Are you tracking it using:

viewer.trackedEntity = entity

If so, that should be instant, so there shouldn't be any loading necessary. If you can post a Sandcastle (https://cesiumjs.org/Cesium/Build/Apps/Sandcastle) example of the delay you're seeing that'd help.

[fruit...@outlook.com]

thanks!
actually I use
viewer.trackedEntity = entity .
I think I take some time to track because loading model, how to know loadding entity success.

[Omar Shehata]

Unfortunately, this isn't something that CesiumJS supports. The ready promise is intentionally hidden in the Entity API. You can see the discussion on that here:

https://github.com/AnalyticalGraphicsInc/cesium/issues/7378

You could use the primitive API as described in that issue, but then you won't be able to use trackedEntity.  

If the model takes a significant time to load, this might be a good reason to tile it up into 3D Tiles (which you can do with Cesium ion https://cesium.com/ion/)

[fruit...@outlook.com]

thanks,I try it