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How to create and use action wrappers

Overview​

This guide provides instructions to create and use an action wrapper in a smart contract.

Code Reference​

See the following code reference guide for action wrapper:

Before you begin​

Make sure you have the following prerequisites in place:

  • An Antelope development environment, for details consult the Documentation Portal.
  • A smart contract named multi_index_example, defined in file multi_index_example.hpp.
  • An action mod which modifies the integer value n stored for row with key user.

Refer to the following reference implementation for your starting point:

class [[eosio::contract]] multi_index_example : public contract {
  // ...
  [[eosio::action]] void mod( name user, uint32_t n );
  // ...
}

Procedure​

Complete the following steps to create and use mod_action action wrapper for the existing mod action in the smart contract:

  1. Define the action wrapper
  2. Use the action wrapper

1. Define The Action Wrapper​

To define an action wrapper for the mod action, use 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>;
  // ...
}

2. Use The Action Wrapper​

2.1. Include Header File​

To use the action wrapper, you have to include the header file where the action wrapper is defined:

#include <multi_index_example.hpp>

2.2. Instantiate The Action Wrapper​

Instantiate the mod_action. Specify the contract to send the action to as the first argument. In this case, it is assumed the contract is deployed to multiindexex account. Specify a structure with 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});

2.3. Send The Action Using The Action Wrapper​

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 example contract.

Summary​

In conclusion, the above instructions show how to create and use action wrapper in a smart contract.