How to set NFT metadata attributes in Unity using C#?

NFT
1

I’m working on an NFT project in Unity and C#. I’ve got a class structure for the metadata, but I’m running into issues when trying to set the attribute values. Here’s what I’ve got so far:

public class NFTMetadata
{
    public string description;
    public string externalUrl;
    public string imageUrl;
    public string nftName;
    public TraitAttribute[] traits;
}

[System.Serializable]
public class TraitAttribute
{
    public string traitName;
    public string traitValue;
}

I’m trying to populate this data in a method like this:

void UpdateNFTData()
{
    NFTMetadata metadata = new NFTMetadata();
    metadata.description = "Cool NFT";
    metadata.imageUrl = "http://example.com/image.png";
    metadata.externalUrl = "http://myproject.com";
    metadata.nftName = "Awesome NFT #1";
    metadata.traits[0].traitName = "Class";
    metadata.traits[0].traitValue = "Warrior";
}

But I keep getting a NullReferenceException when trying to set the trait values. What am I doing wrong here? How can I properly initialize and set these attributes?

2

hey there Hugo_41Cook! i’ve worked with NFTs in Unity before and ran into similar issues. the problem is you’re not initializing the traits array before trying to access it. here’s a quick fix:

void UpdateNFTData()
{
    NFTMetadata metadata = new NFTMetadata();
    metadata.description = "Cool NFT";
    metadata.imageUrl = "http://example.com/image.png";
    metadata.externalUrl = "http://myproject.com";
    metadata.nftName = "Awesome NFT #1";
    
    // Initialize the traits array
    metadata.traits = new TraitAttribute[1];
    metadata.traits[0] = new TraitAttribute();
    metadata.traits[0].traitName = "Class";
    metadata.traits[0].traitValue = "Warrior";
}

this should solve your NullReferenceException. but i’m curious, how many traits are you planning to have for each NFT? have you thought about using a List instead of an array for more flexibility? what kind of NFT project are you working on? sounds interesting!

3

yo hugo, ur close! the issue is u forgot to initialize the traits array. try this:

metadata.traits = new TraitAttribute[1];
metadata.traits[0] = new TraitAttribute();

then set ur values. btw, whats ur nft project about? sounds cool! lemme kno if u need more help

4

I’ve encountered this issue before when working on NFT projects in Unity. The root cause is that you’re not initializing the traits array. Here’s a more robust approach:

void UpdateNFTData()
{
NFTMetadata metadata = new NFTMetadata
{
description = “Cool NFT”,
imageUrl = “http://example.com/image.png”,
externalUrl = “http://myproject.com”,
nftName = “Awesome NFT #1”,
traits = new TraitAttribute
{
new TraitAttribute { traitName = “Class”, traitValue = “Warrior” }
}
};
}

This method uses object initializer syntax, which is more concise and less error-prone. It also allows you to initialize the traits array and its contents in one go. Consider using a List if you need to add traits dynamically in the future.