Developing Smart Contracts for the Ethereum Blockchain

Remix Panels

After seeing how to open the Remix IDE, let’s now see the various panels composing the IDE.

File Explorer

The file explorer provides a view with the created files stored in the browser’s storage. You can rename or delete any file by right-clicking on it, then choosing the right operation from the context menu.

Please note that the file explorer uses the browser’s local storage by default, which means you can lose all your files if you clear or the operating system automatically clears the storage. For advanced work, it’s recommended to use Remixd — a Node.js tool (available from npm npm install -g remixd) which allows the Remix IDE to access your computer’s file system.

Now let’s see the different actions that you can perform using the buttons at the top of the explorer.

Creating/Opening Files in Remix

You can create a new file in the browser local storage using the first button with the + icon on the top left. You can then provide a name in the opened dialog and press OK.

Using the second button from top left, you can open an existing Solidity file from your computer file system into the Remix IDE. The file will also be stored in the browser’s local storage.

Publishing Explorer Files as GitHub Gists

Using the third and fourth buttons from top left, you can publish files from the IDE as a public GitHub gist.

Copying Files to Another Instance of Remix IDE

Using the fifth button from top left, you can copy files from the local storage to another instance of Remix by providing the URL of the instance.

Connecting to the Local File System

The last button can be used to connect the Remix IDE to your local file system if you’re running the Remixd tool.

Solidity Code Editor

The Solidity code editor provides the interface where you can write your code with many features such as syntax highlighting, auto-recompling, auto-saving etc. You can open multiple tabs and also increase/decrease the font size using the +/- button in the top-left corner.

Terminal

The terminal window below the editor integrates a JavaScript interpreter and the web3 object. You can execute JavaScript code in the current context, visualize the actions performed from the IDE, visualize all network transactions or transactions created from the Remix IDE etc. You can also search for data in the terminal and clear the logs.

Tabs Panel

The Tabs panel provides many tabs for working with the IDE:

• the Compile tab: used for compiling a smart contract and publishing on Swarm
• the Run tab: used for sending transactions to the configured environment
• the Settings tab: used for updating settings like the compiler version and many general settings for the editor
• the Debugger tab: used for debugging transactions
• the Analysis tab: used for getting information about the latest compilation
• the Support tab: used for connecting with the Remix community.

Remix Execution Environments

The Remix IDE provides many environments for executing the transactions:

• JavaScript VM: a sandbox blockchain implemented with JavaScript in the browser to emulate a real blockchain.
• Injected Web3: a provider that injects web3 such as Mist and Metamask, connecting you to your private blockchain.
• Web3 Provider: a remote node with geth, parity or any Ethereum client. Can be used to connect to the real network, or to your private blockchain directly without MetaMask in the middle.

Using Remix IDE to Compile and Deploy a Smart Contract

For the sake of demonstrating what we can achieve using Remix IDE, we’ll use an example contract and we’ll see how we can:

• compile the contract in Remix IDE
• see some warnings emitted by the compiler when best practices aren’t followed
• deploy the contract on the JavaScript EVM (Ethereum Virtual Machine)
• make transactions on the deployed contract
• see example reads and writes in the terminal IDE.

We’ll use the following example contract from this tutorial which implements a blockchain raffle:

pragma solidity ^0.4.20;

contract Blocksplit {

    address[] public players;
    mapping (address => bool) public uniquePlayers;
    address[] public winners;

    address public charity = 0xc39eA9DB33F510407D2C77b06157c3Ae57247c2A;

    function() external payable {
        play(msg.sender);
    }

    function play(address _participant) payable public {
        require (msg.value >= 1000000000000000 && msg.value <= 100000000000000000);
        require (uniquePlayers[_participant] == false);

        players.push(_participant);
        uniquePlayers[_participant] = true;
    }

}

The contract declares some variables, such as:

• The players array variable, which holds the addresses of the raffle participants.
• The uniquePlayers mapping, which is used to save unique players so players don’t participate multiple times from the same address. (An address will be mapped to a boolean, true or false, value indicating if the participant has already participated or not.)
• The winners array variable, which will hold the addresses of the winners.
• The charity variable, which holds a hardcoded address of a charity where profits will go.

It also declares:

• A fallback function marked as payable, which enables the smart contract to accept payments.
• A play() function that enables participants to enter the raffle by providing an address.

You can read more details about this contract from this tutorial where all the code is explained in detail.

Now, go ahead and open the Remix IDE from remix.ethereum.org.

Next, create a new file by clicking on the button with the + icon.