cosmos-sdk/docs/build/building-modules/18-define-hooks.md

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Hooks

Hooks are functions that are called before and/or after certain events in the module's lifecycle.

Defining Hooks

1. Define the hook interface and a wrapper implementing depinject.OnePerModuleType:

   https://github.com/cosmos/cosmos-sdk/blob/71c603a2a5a103df00f216d78ec8b108ed64ae28/testutil/x/counter/types/expected_keepers.go#L5-L12
   

2. Add a CounterHooks field to the keeper:

   https://github.com/cosmos/cosmos-sdk/blob/71c603a2a5a103df00f216d78ec8b108ed64ae28/testutil/x/counter/keeper/keeper.go#L25
   
   

3. Create a depinject invoker function

   https://github.com/cosmos/cosmos-sdk/blob/71c603a2a5a103df00f216d78ec8b108ed64ae28/testutil/x/counter/depinject.go#L53-L75   
   

4. Inject the hooks during app initialization:

   appConfig = appconfig.Compose(&appv1alpha1.Config{
       Modules: []*appv1alpha1.ModuleConfig{
           // ....
           {
               Name:   types.ModuleName,
               Config: appconfig.WrapAny(&types.Module{}),
           },
       }
   })
   appConfig = depinject.Configs(
       AppConfig(),
       runtime.DefaultServiceBindings(),
       depinject.Supply(
           logger,
           viper,
           map[string]types.CounterHooksWrapper{
               "counter": types.CounterHooksWrapper{&types.Hooks{}},
           },
   ))
   

Examples in the SDK

For examples of hooks implementation in the Cosmos SDK, refer to the Epochs Hooks documentation and Distribution Hooks Documentation.