👍Runtime Events

How to tell someone using your blockchain something happened.

Users of the application need feedback about what happened when they clicked something or interacted on your chain through a public endpoint you've given them.

Transactions can fail for any number of reasons, so your users need to know and that is handled through and Event. Confirmations are similar: tell your user it went okay with an Event.

Right, so my pallet should be able to emit Events?

Yep, pretty much without exception. Here's how:

In the Pallet

type Event

Add Event type to the `Config:

// Note: this is the pallet-required `Configuration Trait`
pub trait Config: frame_system::Config {
    
    // copy the line below exactly as shown into the `Config` section
    // of your `Pallet`. You'll eventually be able to interpret that
    // if you don't lnow. Just keep truckin'.
    type Event: From<Event> + Into<<Self as frame_system::Config>::Event>;

}

decl_module!

And now add the decl_module! ("declare_module") macro to give access to the deposit_event() method.

decl_module! {
pub struct Module<T: Config> for enum Call where origin: T::Origin {

    // This line is new
    fn deposit_event() = default;

    // More dispatchable calls that you compose woud go here
    }
}

Reminder: the decl_module! macro is the same we used for creating Dispatchable Calls for a Pallet.

decl_event!

decl_event! ("declare event") macro is the way Rust implements an event

decl_event!(
    pub enum Event<T> where AccountId = <T as frame_system::Config>::AccountId {
        EmitInput(AccountId, u32),
    }
);

We are showing generic types in these examples. The syntax for generic events requires the where.

In the Runtime

We've defined a trait in the Pallet for Config and so now it has to be implemented at runtime.

In your runtime lib.rs file, add

./runtime/src/lib.rs

impl simple_event::Config for Runtime {
    type Event = Event;
}

The code above is simply specifying the type for Event . Note the <T> is not shown and that is because we are defining the concrete type to be implemented by the Pallet we're configuring.

Add the events to the runtime build macro construct_runtime! by adding:

construct_runtime!(
    pub enum Runtime where
        Block = Block,
        NodeBlock = opaque::Block,
        UncheckedExtrinsic = UncheckedExtrinsic
    {
        // --snip--
        YourEventName: your_pallet_name,
    }
);