Event declaration in Blockchain / Solidity - Mini Project: Build & Apply

Event Declaration in Solidity

📖 Scenario: You are building a simple smart contract for a blockchain application. You want to notify users when a new user registers by using an event.

🎯 Goal: Create a Solidity contract that declares an event called UserRegistered with two parameters: address userAddress and string userName. Then emit this event when a new user registers.

📋 What You'll Learn

Declare an event named UserRegistered with parameters address userAddress and string userName

Create a public function registerUser that takes a string memory userName as input

Emit the UserRegistered event inside the registerUser function with the sender's address and the userName

Print the event declaration and the function emitting the event

💡 Why This Matters

🌍 Real World

Events in smart contracts are like signals that tell external apps when something important happens, such as a user registering or a transaction completing.

💼 Career

Understanding event declaration and emission is essential for blockchain developers to build interactive and responsive decentralized applications.

1

Declare the UserRegistered event

Declare an event called UserRegistered with parameters address userAddress and string userName inside the contract named UserRegistry.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserRegistry {
    // Declare the UserRegistered event here
}

Need a hint?

Use the event keyword followed by the event name and parameters inside the contract.

2

Create the registerUser function

Add a public function called registerUser that takes a string memory userName as input inside the UserRegistry contract.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserRegistry {
    event UserRegistered(address userAddress, string userName);

    // Add the registerUser function here
}

Need a hint?

Define a function with the public visibility and a string memory parameter.

3

Emit the UserRegistered event inside registerUser

Inside the registerUser function, emit the UserRegistered event with msg.sender as userAddress and the input userName.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserRegistry {
    event UserRegistered(address userAddress, string userName);

    function registerUser(string memory userName) public {
        // Emit the UserRegistered event here
    }
}

Need a hint?

Use the emit keyword followed by the event name and parameters.

4

Test the event emission

Add a comment line with // Event UserRegistered declared and emitted on user registration to confirm the event is declared and emitted correctly.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserRegistry {
    event UserRegistered(address userAddress, string userName);

    function registerUser(string memory userName) public {
        emit UserRegistered(msg.sender, userName);
    }
    // Add a comment confirming event declaration and emission
}

Need a hint?

Add a comment line to confirm the event is declared and emitted.