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Introduction to ERC-721 (NFT) Smart Contracts

This tutorial will start you with a basic ERC-721 (NFT) smart contract on the Avalanche Network, regardless of your previous development experience. We'll deploy our NFT on the Metal Tahoe Testnet and view it on the MetalScan Testnet Explorer. Note that these aren't transferable to the Mainnet. However, once you feel comfortable launching your project, you can do so on Metal Mainnet and list it on an NFT marketplace.

The following tools will be used during this tutorial:

caution

DISCLAIMER: This Solidity smart contract tutorial is for demonstration purposes only. Users should consider proper precautions, error handling, and safeguards for production use. No one at Metal Blockchain is responsible for your development, and you must take full responsibility for ensuring your code is secure. :::

Preparing Your NFT Files​

The first step of setting up an NFT smart contract is having your NFT files ready to use. In this example, the files will get uploaded to Pinata, a pinning service that prevents files from being garbage collected on IPFS.

If you're unfamiliar with the process of uploading image and metadata files to an IPFS provider for NFT collection usage, please check out this article on preparing NFT files. Ensure that your files are uploaded and your base URI is ready to plug into your smart contract.

Once the image and metadata files are ready, we can prepare to deploy a smart contract.

Preparing Your Environment​

MetaMask Extension​

You'll need the MetaMask Extension installed on whatever browser you're using to be able to fund the deployment of the smart contract. If you've not done so already, download MetaMask and add the Tahoe network to MetaMask. Create or import a Tahoe account as necessary.

Getting Testnet Funds​

Because we're deploying on the Tahoe Network, you'll need to get METAL on the Tahoe network. If you visit the Metal Faucet, you can request up to 2 Tahoe METAL per day. Please enter the C Chain address of the account linked to your MetaMask in the previous step.

Avalanche Faucet

Creating the Smart Contract​

To create the smart contract, we're going to use Open Zeppelin. Open Zeppelin is a key tool for building smart contracts quickly and easily. While we're only scratching the surface in this tutorial, ample documentation is available on their website for you to read when you want to build more complex contracts.

Open Zeppelin provides a Contract Wizard that will build out ERC contracts. To avoid any complex coding environments, we'll use this to create our ERC-721 contract.

Contract Wizard

Select ERC-721 on the Contract Wizard to get started. This will create the contract in the Solidity programming language.

As you can see, the template contract is bare-boned. We'll fill out the information in the left panel to auto-populate it into our contract. Make sure you change to the ERC-721 tab as you get started to make the proper contract.

The Wizard auto-fills in a name and symbol for your NFT collection, which we'll modify here. I'm naming it Photography and giving it the symbol FOTO. If you chose your own files to use during this tutorial, you can choose a relevant name and symbol for your collection.

The Base URI field listed here is the URL of the metadata folder uploaded to Pinata(for example, ours is https://gateway.pinata.cloud/ipfs/QmYdWxbiwsfsYcW1CYQPgYujAc9FMLPG3fgFcxFskbSsFa). Paste that into the Base URI field. After the Wizard adds our variables to the template, our contract should look like this:

Contract Wizard Populated

Next, we'll want to check the Mintable and Auto Increment Ids boxes. This will populate a mint function into our template that would handle the incrementing of token Ids on mint if we had more than one NFT in our collection. We still want it to auto-assign our 1 NFT, so we'll check it.

This automatically checks the Ownable button, which gives the safeMint function the onlyOwner modifier. This modifier indicates that only the owner of the smart contract will be able to successfully call the function.

Note: This modifier should be removed when creating a smart contract for a public mint. Otherwise, users wouldn't be able to successfully mint the NFTs when calling the safeMint function. This tutorial only handles the owner’s wallet address, so it is being left in.

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Now, our contract is a little more populated:

Contract Wizard SafeMint

For this simple example, we'll not add any additional functionality to the safeMint function. Currently, it mints one NFT to the address specified in the function call. There is no cost to mint the NFT other than the gas fee for the transaction itself.

This safeMint function currently doubles as an airdrop function because the address the NFT is minted to does not need to be the function owner. This functionality becomes very useful when NFT collection owners want to give away NFTs for free outside of the normal minting window.

At this point, our smart contract is ready. At the top, you can click Open in Remix to get ready to deploy your smart contract.

Contract Wizard Open Remix

Deploying the Smart Contract with Remix​

Remix IDE is a solidity compiler that allows you to edit, compile, and deploy your smart contract. This will prevent you from needing to download any other coding environments at this stage.

Once you've imported your contract, the first thing you need to do is compile it. Hit the Compile button on the left-hand side. You could also use the keyboard shortcut Ctrl / Command + S.

Remix Compile

Once completed, you'll get a green checkmark on the far left tab and will see options to Publish on IPFS or Swarm. Those aren't important to our tutorial. Next, you'll click on the bottom tab on the left-hand side to move to the deployment page.

Remix Deploy Page

Now, we need to change the environment that Remix will try to use to deploy the smart contract. Click on the Environment drop-down, and select Injected web3.

Remix Web3

This should prompt you to connect with your MetaMask account. Once connected, you can verify the correct connection by checking that the Account number matches your MetaMask address.

Remix MetaMask

Now click on the Contract drop-down and select the contract you created and compiled. It should show up with the name you gave it in the Open Zeppelin Wizard.

Remix Contract

Now, click deploy. This will open MetaMask and ask you to confirm the transaction. Click Confirm.

MetaMask Accept

It may take a second, but once completed, your newly deployed contract will appear underneath the Transactions Recorded field.

Remix Record

Copy your contract’s address and open the MetalScan Testnet Explorer. Paste your contract address in the search bar, and click Search.

You'll now see your contract information on MetalScan. The first transaction you see should be the contract deployment you just did in the Remix IDE.

MetalScan

Minting an NFT​

Now that you've deployed the contract, you can mint the NFT. Go back to the Remix IDE tab and click on your contract to expand its information. A list of functions will appear that you can interact with.

Remix Functions

The only function you're interested in is the safeMint function. Click the drop-down arrow for the function to expand the address field.

Remix safe mint

Now, copy your MetaMask address and paste it into this address field. This will send the NFT to your address when the mint function is called. After, hit transact.

This will reopen MetaMask and ask you to verify the transaction. Click Confirm to mint your NFT.

Confirm Mint

Once the transaction has been confirmed, you'll see a green checkmark in the terminal at the bottom of the Remix IDE.

Remix Confirm Mint

Head back to the MetalScan Testnet explorer page for your contract and refresh it. You should now see a second transaction, your call to safeMint.

MetalScan Mint

By clicking on the TX Hash, you see that your NFT was created!

MetalScan Transaction

Mainnet​

All of the above steps can be used on Mainnet except the following changes: