How do we use topics in events?

问题

I am trying to use deposit_event_indexed method when depositing an event with a specific topic so that I can use something like the polkadot.js' api.query.system.eventTopics to fetched indexed events.

However, I get the following error

63  | |  Self::deposit_event_indexed(&eventHashArray, RawEvent::TestIndexedEvent());
    | |        ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `Module<T>`

I am also quite new to rust, so from my understanding, according to the doc, this method is part of the Module's trait. Please help!

回答1:

Assuming you are calling deposit_event_indexed from your custom pallet, you simply need to target the function which is located in the frame_system pallet.

frame_system::Module::<T>::deposit_event_indexed(...)

Unlike the more commonly used deposit_event feature, we do not automatically import this into your pallet, which is why you see this error.

来源：https://stackoverflow.com/questions/60720925/how-do-we-use-topics-in-events