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How to create and use action wrappers

  1. Start with a contract multi_index_example which has an action mod defined like below in file multi_index_example.hpp; the action modifies the integer value n stored for row with key user.
class [[eosio::contract]] multi_index_example : public contract {
  // ...
  [[eosio::action]] void mod( name user, uint32_t n );
  // ...
}
  1. To define an action wrapper for the mod action, make use of the eosio::action_wrapper template, with the first parameter the action name as a eosio::name and second parameter as the reference to the action method
class [[eosio::contract]] multi_index_example : public contract {
  // ...
  [[eosio::action]] void mod(name user);
  // ...
+  using mod_action = action_wrapper<"mod"_n, &multi_index_example::mod>;
  // ...
}
  1. To use the action wrapper, you have to include the header file where the action wrapper is defined
#include <multi_index_example.hpp>
  1. Then instantiate the mod_action defined above, specifying the contract to send the action to as the first argument. In this case, it is assumed the contract is deployed to multiindexex account, and a structure which is defined by two parameters: the self account, obtained by get_self() call, and the active permission (you can modify these two parameters based on your requirements).
#include <multi_index_example.hpp>

+multi_index_example::mod_action modaction("multiindexex"_n, {get_self(), "active"_n});
  1. And finally call the send method of the action wrapper and pass in the mod action's parameters as positional arguments
#include <multi_index_example.hpp>

multi_index_example::mod_action modaction("multiindexex"_n, {get_self(), 1});

+modaction.send("eostutorial"_n, 1);

For a full example see the multi_index contract implementation.