How to write to a smart contract

Writing to smart contracts is an essential part of interacting with decentralized applications. It allows you to modify the state of the contract by executing transactions and invoking methods that change the data stored on the blockchain. This is useful when you need to store new information, update existing data, or execute specific functions within your application.

The example provided at the path above demonstrates how to write to smart contracts using the EmergenceSDK in Unity. The provided example shows how to create a ContractInfo object, and call the WriteMethod to execute a smart contract method with the provided input data.

First, import the necessary namespaces:

using EmergenceSDK.Runtime.Internal.Utils;
using EmergenceSDK.Runtime.ScriptableObjects;
using EmergenceSDK.Runtime.Services;
using UnityEngine;

These namespaces contain various utilities, scriptable objects and services needed to interact with the EmergenceSDK in Unity.

Next, define a new class called WritingContracts, which inherits from MonoBehaviour. This allows you to attach this script to a GameObject in Unity.

public class WritingContracts : MonoBehaviour
{
    [Header("Contract information")]
    // This must be set in the inspector
    public DeployedSmartContract deployedContract;
    // Public string array that is used as input data for the smart contract method
    public string[] body = new string[] { };
    // Public string that is used as input data for the smart contract method
    public string value = "0";

    private IContractService contractService;

    ...
}

Declare the following variables:

• deployedContract: A public DeployedSmartContract variable that must be set in the Unity inspector. There are examples that you can use in the sample project.
• body: A public string array that serves as input data for the smart contract method, this will need to change based on the contract chosen.
• value: A public string that serves as input data for the smart contract method, this will need to change based on the contract chosen.
• contractService: A private IContractService variable for interacting with the contract-related services provided by EmergenceSDK.

In the Awake method, initialize the contractService variable by getting the IContractService instance from the EmergenceServiceProvider class.

public void Awake()
{
    contractService = EmergenceServiceProvider.GetService<IContractService>();
}

The Start method is called at the beginning of the script’s execution. Here, we call the WriteContract method to initiate the contract writing process.

public void Start()
{
    WriteContract();
}

The WriteContract method creates ContractInfo using the deployedContract variable and calls contractService.WriteMethod once its created. ContractService.WriteMethod takes a callback method to be used upon successful contract write. We’ll use OnWriteSuccess for this.

public void WriteContract()
{
    // Creates a ContractInfo object with the smart contract address, method name, network name, and default node URL
    var contractInfo = new ContractInfo(deployedContract, "[METHOD NAME]");

    // Calls the ReadMethod method to execute the smart contract method defined in the ABI with an empty input parameter
    contractService.WriteMethod(contractInfo, value, body, OnWriteSuccess, EmergenceLogger.LogError);
}

The OnWriteSuccess method is called when the WriteMethod method executes successfully. It logs the response to the console.

private void OnWriteSuccess(BaseResponse<string> response)
{
    // Logs the response to the console
    Debug.Log($"{response}");
}

By following this example, you can write to smart contracts in your Unity project using the EmergenceSDK. The process involves creating a ContractInfo object, and calling the WriteMethod to execute a smart contract method with the provided input data. This allows you to modify the contract’s state, store new information, update existing data, or execute specific functions within your application.

Full code:

using EmergenceSDK.Runtime.Internal.Utils;
using EmergenceSDK.Runtime.ScriptableObjects;
using EmergenceSDK.Runtime.Services;
using EmergenceSDK.Runtime.Types.Responses;
using UnityEngine;

namespace EmergenceSDK.Samples.CoreSamples.Examples
{
    public class WritingContracts : MonoBehaviour
    {
        [Header("Contract information")]
        // This must be set in the inspector
        public DeployedSmartContract deployedContract;
        // Public string array that is used as input data for the smart contract method
        public string[] body = new string[] { };
        // Public string that is used as input data for the smart contract method
        public string value = "0";

        private IContractService contractService;
        
        public void Awake()
        {
            contractService = EmergenceServiceProvider.GetService<IContractService>();
        }

        public void Start()
        {
            WriteContract();
        }

        // This method is called once the contract is loaded
        private void WriteContract()
        {
            // Creates a ContractInfo object with the smart contract address, method name, network name, and default node URL
            var contractInfo = new ContractInfo(deployedContract, "[METHOD NAME]");

            // Calls the ReadMethod method to execute the smart contract method defined in the ABI with an empty input parameter
            contractService.WriteMethod(contractInfo, value, body, OnWriteSuccess, EmergenceLogger.LogError);
        }

        private void OnWriteSuccess(BaseResponse<string> response)
        {
            // Logs the response to the console
            EmergenceLogger.LogInfo($"{response}");
        }
    }
}