Here is my code. FluidTankHandler#fill fills the holding FluidTank in order, but that doesn't seem to work. The behavior I want to implement is that when the first FluidTank is full, the second FluidTank will be filled. However, now it is put in every Fluid Tank one by one, and after that, the water does not increase no matter how many times it is repeated. Does anyone know what's going on?

 

FluidTankHandler class: https://github.com/Zemelua/UMU-Mod/blob/main/src/main/java/io/github/zemelua/umumod/fluid/FluidTankHandler.java

Mod fluid capability: https://github.com/Zemelua/UMU-Mod/blob/main/src/main/java/io/github/zemelua/umumod/capability/UMUCapabilities.java

BackpackItem class (Testing FluidTankHandler behavior in onItemUse method: https://github.com/Zemelua/UMU-Mod/blob/main/src/main/java/io/github/zemelua/umumod/item/BackpackItem.java

I did some research, but the data is still not saved ... The data of ItemStackHandler seems to be saved properly. When is IStorage#writeNBT called and where does the instance passed to the instance get from? The instance may not have been passed in properly and may not be able to save the data.

I think the problem is here(https://github.com/Zemelua/UMU-Mod/blob/main/src/main/java/io/github/zemelua/umumod/capability/storage/FluidTankHandlerStorage.java). The instance argument passed by IStorage#writeNBT is incorrect. When is this method called? Where do the passed arguments come from? I'm sorry to repeat, but please help me someone.