How to interact with Smart Contract deployed on Blockchain from Swift app - swift

Question

It is my first time working with smart contracts and my goal is to create a mobile app which can interact with it by calling methods to save or retrieve data. For this reason I have created a very simple contract using Remix and I have also deployed on Rinkeby testnet.
contract Storage {
uint256 number;
function store(uint256 num) public {
number = num;
}
function retrieve() public view returns (uint256){
return number;
}
}
Then I built a SwiftUI app, which has one button. When I press this button, I want to call the store method and save some int number. For example number 9. Therefore I have created a function called write which looks as following:
let myInt = 9
func write() {
let web3 = Web3.InfuraRinkebyWeb3(accessToken: "https://rinkeby.infura.io/v3/a146daf63d93490995823f0910f50118")
let walletAddress = EthereumAddress("0xc65943Fae5a554e7DCF916F8828a73E5f7b1bDCd")! // Your wallet address
let contractMethod = "store" // Contract method you want to write
let contractABI = contractABIString // Contract ABI
let contractAddress = EthereumAddress("0x2826C42354FE5B816c7E21AD9e3B395Ced512C0C")!
let abiVersion = 2 // Contract ABI version
let parameters = [myInt] as [AnyObject]
let extraData: Data = Data() // Extra data for contract method
let contract = web3.contract(contractABI, at: contractAddress, abiVersion: abiVersion)!
var options = TransactionOptions.defaultOptions
options.from = walletAddress
options.gasPrice = .automatic
options.gasLimit = .automatic
do {
contract.write(
contractMethod,
parameters: parameters,
extraData: extraData,
transactionOptions: options)
} catch {
print("error:", error)
}
Unfortunately, when I run this code, nothing is happening. I don't get any error but when I refresh the contract I see that number 9 is not passed.
I am using web3swift library, https://github.com/skywinder/web3swift/tree/master#send-erc-20-token. According to the documentation, it should be fine, but it is not working, therefore I would really appreciate some assistant to make it work or some example projects where I can take a look, because I also couldn't find anything.
I found some other project using JS and I see the people there use their private keys, maybe I also need it, but since it is not shown in the documentation, I was not sure how to use it.

Answer 1

The smart contract interaction requires a few initialisations steps:
Your wallet
KeyStoreManager
web3
Let's assume you already got a Metamask wallet.
Separately you need to have a separate file containing the ABI of the smartContract you want to interact with.
It is an array and having it in a Swift.String is easier.(I won't show you this step)
struct Wallet {
let address: String
let data: Data
let name: String
let isHD: Bool
}
class SmartContractInteraction {
var wallet: Wallet!
var keystoreManager: KeystoreManager!
var web3: web3!
init() {
wallet = initializeWallet()
keystoreManager = getKeyStoreManager()
web3 = initializeweb3()
}
private func initializeWallet() -> Wallet? {
let password = "PasswordMetamask"
let key = "AccountPrivateKey"
let formattedKey = key.trimmingCharacters(in: .whitespacesAndNewlines)
let dataKey = Data.fromHex(formattedKey)!
let name = "Account 1"
do {
let keystore = try EthereumKeystoreV3(privateKey: dataKey, password: password)!
let keyData = try JSONEncoder().encode(keystore.keystoreParams)
let address = keystore.addresses!.first!.address
return Wallet(address: address, data: keyData, name: name, isHD: false)
} catch {
print("wallet init failed: \(error)")
return nil
}
}
private func getKeyStoreManager() -> KeystoreManager {
let data = wallet.data
let keystoreManager: KeystoreManager
if wallet.isHD {
let keystore = BIP32Keystore(data)!
keystoreManager = KeystoreManager([keystore])
} else {
let keystore = EthereumKeystoreV3(data)!
keystoreManager = KeystoreManager([keystore])
}
return keystoreManager
}
private func initializeweb3() -> web3 {
let endpoint = "https://ropsten.infura.io/v3/....."
let web3 = web3swift.web3(provider: Web3HttpProvider(URL(string: endpoint)!)!)
web3.addKeystoreManager(keystoreManager)
return web3
}
func callSmartContract() {
let value: String = "1"
let walletAddress = EthereumAddress(wallet.address)!
let contractAddress = EthereumAddress("SmartContractAddress")!
let contractMethod = "store"
let contractABI = MyContractABI
let abiVersion = 2
let parameters = [9] as [AnyObject]
let extraData: Data = Data()
let contract = web3.contract(contractABI, at: contractAddress, abiVersion: abiVersion)!
let amount = Web3.Utils.parseToBigUInt(value, units: .wei)
var options = TransactionOptions.defaultOptions
options.value = amount
options.from = walletAddress
options.gasPrice = .automatic
options.gasLimit = .automatic
let tx = contract.write(
contractMethod,
parameters: parameters,
extraData: extraData,
transactionOptions: options)!
do {
let password = "MetamaskPassword"
let result = try tx.send(password: password)
print(result)
} catch {
print("Token Balance failed: \(error)")
}
}
}
Like this should work, I think passing the value/option.value in the smartContract call method isn't necessary, but since I don't have your ABI I prefer to not remove anything from how it worked for me. Also I am not sure about the type of the number you pass.
Feel free to edit if this works without :)