How to Integrate with the Ethereum Blockchain using Android

#Installation

To interact with the Ethereum blockchain, Magic Android SDK integrates Web3j as sub dependency.

Add the following dependencies in build.gradle

Java

01dependencies {

02    implementation 'link.magic:magic-android:4.0.0'

03    implementation 'org.web3j:core:4.8.8-android'

04    implementation 'org.web3j:geth:4.8.8-android'

05}

#Initialization

The Magic class is the entry-point to the Magic SDK. It must be instantiated with a Magic publishable key.

note

The following example uses Kotlin 1.3 and Magic Android 4.x. Android demo will be open-sourced soon. You may use Android Studio to convert Java to Kotlin or vice versa.

Kotlin

01class MagicDemoApp: Application() {

03    lateinit var magic: Magic

04    override fun onCreate() {

05        magic = Magic(this, "YOUR_PUBLISHABLE_KEY")

06⁠        super.onCreate()

07    }

08}

10// Initialize web3j

11class MagicActivity: AppCompatActivity() {

13    lateinit var web3j: Web3j

14    lateinit var gethWeb3j: Geth

16    override fun onCreate(savedInstanceState: Bundle?) {

17        super.onCreate(savedInstanceState)

18        web3j = Web3j.build(magic.rpcProvider)

19        gethWeb3j = Geth.build(magic.rpcProvider)

20    }

21}

#Use Different Networks

#Testnet

Goerli Block Explorer: https://goerli.etherscan.io

⁠Goerli Testnet Faucet: https://goerlifaucet.com

Kotlin

01magic = Magic(this, "YOUR_PUBLISHABLE_API_KEY", Magic.Network.goerli)

You can allow specific URLs to interact with the Magic SDK, such as a custom RPC URL to send transactions to your node. The Content Security Policy (CSP) of a browser dictates what resources can be loaded. If you're using a Dedicated Wallet, you can update the policy in the settings page of the dashboard with your custom URL. If you're using a Universal Wallet, please reach out to support to get your URL added.

important

The use of a custom node will require the RPC URL to the project's Content Security Policy from your Magic dashboard. Refer to the CSP documentation.

Kotlin

01magic = Magic(this, "YOUR_PUBLISHABLE_API_KEY", CustomNodeConfiguration("https://alchemy.io"))

important

Do not set the custom nodes to local IP address (E.x. "http://127.0.0.1"\), because local IP will point to the network environment inside mobile device / simulator. Try accessible IP address in the same Wifi/Internet Environment (E.x. "http://10.0.0.93:3000"\)

#Associated Class

CustomNodeConfiguration(rpcUrl: String, chainId: Int?)

rpcUrl: Your own node URL
chainId: Your own node's chainId

Magic.EthNetwork

Swift

01enum class EthNetwork {

02        Mainnet, Goerli

03 }

#Common Methods

#Send Transaction

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var magic: Magic

04    lateinit var web3j: Web3j

06    override fun onCreate(savedInstanceState: Bundle?) {

07        super.onCreate(savedInstanceState)

08        magic = (applicationContext as MagicDemoApp).magic

09        web3j = Web3j.build(magic.rpcProvider)

10    }

12    // After user is successfully authenticated

13    fun sendTransaction(v: View) {

14        try {

15            val value: BigInteger =  Convert.toWei("0.5", Convert.Unit.ETHER).toBigInteger()

16            val transaction = createEtherTransaction(account, BigInteger("1"), BigInteger("21000"), BigInteger("21000"), account, value)

17            val receipt = web3j.ethSendTransaction(transaction).send()

18            Log.d("Transaction complete: " + receipt.transactionHash)

19        } catch (e: Exception) {

20            Log.e("Error", e.localizedMessage)

21        }

22    }

23}

#Sign Message

Magic Android SDK extends the functionality from Web3j to allow developers to sign Typed Data. You may find it in magic.web3jSigExt

#Personal Sign

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var magic: Magic

04    lateinit var web3j: Web3j

05    lateinit var gethWeb3j: Geth

07    // After user is successfully authenticated

08    private var account: String? = null

10    override fun onCreate(savedInstanceState: Bundle?) {

11        super.onCreate(savedInstanceState)

12        magic = (applicationContext as MagicDemoApp).magic

13        web3j = Web3j.build(magic.rpcProvider)

14        gethWeb3j = Geth.build(magic.rpcProvider)

15    }

17    fun personSign(view: View) {

18        val message = "Hello from Magic!!!"

19        val personalSign: PersonalSign = gethWeb3j.personalSign(

20                message, account, "password")

21                .send()

22        Log.d("Magic", "Signed Message: " + personalSign.signedMessage)

24        // Recover Message

25        val recovered = gethWeb3j.personalEcRecover(message, personalSign.signedMessage).send()

26        Log.d("Magic", "Recovered Address: " + recovered.recoverAccountId)

27    }

28}

#Sign TypedData Legacy (V1)

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var magic: Magic

05    // After user is successfully authenticated

06    private var account: String? = null

08    override fun onCreate(savedInstanceState: Bundle?) {

09        super.onCreate(savedInstanceState)

10        magic = (applicationContext as MagicDemoApp).magic

11    }

13    // Sign with EIP712 Data Field

14    fun signTypedDataLegacy(v: View) {

15        val list = listOf(

16                EIP712TypedDataLegacyFields("string", "Hello from Magic", "This message will be signed by you"),

17                EIP712TypedDataLegacyFields("uint32", "Here is a number", "90210")

18        )

19        val signature = magic.web3jSigExt.signTypedDataLegacy(account, list).send()

20        Log.d("Magic", signature.result)

21    }

23    // Sign with JSON String

24    fun signTypedDataLegacyJson(v: View) {

25        val jsonString = "[{\"type\":\"string\",\"name\":\"Hello from Magic\",\"value\":\"This message will be signed by you\"},{\"type\":\"uint32\",\"name\":\"Here is a number\",\"value\":\"90210\"}]"

26        val signature = magic.web3jSigExt.signTypedDataLegacy(account, jsonString).send()

27        Log.d("Magic", signature.result)

28    }

29}

#Sign Typed Data v3

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var magic: Magic

04    lateinit var web3j: Web3j

05    lateinit var gethWeb3j: Geth

07    // After user is successfully authenticated

08    private var account: String? = null

10    override fun onCreate(savedInstanceState: Bundle?) {

11        super.onCreate(savedInstanceState)

12        magic = (applicationContext as MagicDemoApp).magic

13    }

15    fun signTypedData(v: View) {

16        val jsonString = "{\"types\":{\"EIP712Domain\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"version\",\"type\":\"string\"},{\"name\":\"verifyingContract\",\"type\":\"address\"}],\"Order\":[{\"name\":\"makerAddress\",\"type\":\"address\"},{\"name\":\"takerAddress\",\"type\":\"address\"},{\"name\":\"feeRecipientAddress\",\"type\":\"address\"},{\"name\":\"senderAddress\",\"type\":\"address\"},{\"name\":\"makerAssetAmount\",\"type\":\"uint256\"},{\"name\":\"takerAssetAmount\",\"type\":\"uint256\"},{\"name\":\"makerFee\",\"type\":\"uint256\"},{\"name\":\"takerFee\",\"type\":\"uint256\"},{\"name\":\"expirationTimeSeconds\",\"type\":\"uint256\"},{\"name\":\"salt\",\"type\":\"uint256\"},{\"name\":\"makerAssetData\",\"type\":\"bytes\"},{\"name\":\"takerAssetData\",\"type\":\"bytes\"}]},\"domain\":{\"name\":\"0x Protocol\",\"version\":\"2\",\"verifyingContract\":\"0x35dd2932454449b14cee11a94d3674a936d5d7b2\"},\"message\":{\"exchangeAddress\":\"0x35dd2932454449b14cee11a94d3674a936d5d7b2\",\"senderAddress\":\"0x0000000000000000000000000000000000000000\",\"makerAddress\":\"0x338be8514c1397e8f3806054e088b2daf1071fcd\",\"takerAddress\":\"0x0000000000000000000000000000000000000000\",\"makerFee\":\"0\",\"takerFee\":\"0\",\"makerAssetAmount\":\"97500000000000\",\"takerAssetAmount\":\"15000000000000000\",\"makerAssetData\":\"0xf47261b0000000000000000000000000d0a1e359811322d97991e03f863a0c30c2cf029c\",\"takerAssetData\":\"0xf47261b00000000000000000000000006ff6c0ff1d68b964901f986d4c9fa3ac68346570\",\"salt\":\"1553722433685\",\"feeRecipientAddress\":\"0xa258b39954cef5cb142fd567a46cddb31a670124\",\"expirationTimeSeconds\":\"1553808833\"},\"primaryType\":\"Order\"}"

17        val signature = magic.web3jSigExt.signTypedData(account, jsonString).send()

18        Log.d("Magic", "Signature: " + signature.result)

19    }

20}

#Sign Typed Data v4

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var magic: Magic

04    lateinit var web3j: Web3j

05    lateinit var gethWeb3j: Geth

07    // After user is successfully authenticated

08    private var account: String? = null

10    override fun onCreate(savedInstanceState: Bundle?) {

11        super.onCreate(savedInstanceState)

12        magic = (applicationContext as MagicDemoApp).magic

13    }

15    fun signTypedDataV4(v: View) {

16        val jsonString = "{\"domain\":{\"chainId\":1,\"name\":\"Ether Mail\",\"verifyingContract\":\"0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC\",\"version\":\"1\"},\"message\":{\"contents\":\"Hello, Bob!\",\"from\":{\"name\":\"Cow\",\"wallets\":[\"0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826\",\"0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF\"]},\"to\":[{\"name\":\"Bob\",\"wallets\":[\"0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB\",\"0xB0BdaBea57B0BDABeA57b0bdABEA57b0BDabEa57\",\"0xB0B0b0b0b0b0B000000000000000000000000000\"]}]},\"primaryType\":\"Mail\",\"types\":{\"EIP712Domain\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"version\",\"type\":\"string\"},{\"name\":\"chainId\",\"type\":\"uint256\"},{\"name\":\"verifyingContract\",\"type\":\"address\"}],\"Group\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"members\",\"type\":\"Person[]\"}],\"Mail\":[{\"name\":\"from\",\"type\":\"Person\"},{\"name\":\"to\",\"type\":\"Person[]\"},{\"name\":\"contents\",\"type\":\"string\"}],\"Person\":[{\"name\":\"name\",\"type\":\"string\"},{\"name\":\"wallets\",\"type\":\"address[]\"}]}}"

17        val signature = magic.web3jSigExt.signTypedDataV4(account, jsonString).send()

18        Log.d("Magic", "Signature: " + signature.result)

19    }

20}

#Get User Info

Kotlin

01class MagicActivity: AppCompatActivity() {

03    lateinit var web3j: Web3j

05    override fun onCreate(savedInstanceState: Bundle?) {

06        super.onCreate(savedInstanceState)

07        magic = (applicationContext as MagicDemoApp).magic

08        web3j = Web3j.build(magic.rpcProvider)

09    }

11    // After user is successfully authenticated

12    fun getAccount(){

13        try {

14            val accounts = web3j.ethAccounts().sendAsync()

16            accounts.whenComplete { accRepsonse: EthAccounts?, error: Throwable? ->

17                if (error != null) {

18                    Log.e("MagicError", error.localizedMessage)

19                }

20                if (accRepsonse != null && !accRepsonse.hasError()) {

21                    account = accRepsonse.accounts[0]

22                    Log.d("Magic", "Your address is $account")

23                }

24            }

25        } catch (e: Exception) {

26            Log.e("Error", e.localizedMessage)

27        }

28    }

29}

#Smart Contract

In this example, we'll be demonstrating how to use Magic with Web3j to interact with Solidity smart contracts. The simple Hello World contract allows anyone to read and write a message to it.

Solidity

01pragma solidity ^0.5.10;

03contract HelloWorld {

05  string public message;

07  constructor(string memory initMessage) public {

08    message = initMessage;

09  }

11  function update(string memory newMessage) public {

12    message = newMessage;

13  }

14}

#Create a Kotlin/Java Contract Class from ABI

Web3j supports the auto-generation of smart contract function wrappers in Java from Solidity ABI files.

To get started, you must have two files

ABI JSON file <Contract>.json
ByteCode file <Contract>.bin

#Install web3j cli-tool

Bash

01$ curl -L https://get.web3j.io | sh

You may need to install a JDK to support this library

After it has been installed to your computer, you may run the following command to check

Bash

01$ web3j version

#Create the contract class

Bash

01$ web3j solidity generate -a=./path/to/<Contract>.json -b=./path/to/<Contract>.bin -o=/output/path/ -p={packageName}

You’ll find a Contract.java file created in your output directory above. Put this file in your project, and no more changes are needed.

For more details about this section, please click here.

#Deploy Contract

When deploying contract, building or interacting with a contract using web3j library, Magic offers MagicTxnManager class as a default TransactionManager that helps you to avoid dealing with private keys or credentials that Contract class requires.

Kotlin

01import link.magic.demo.contract.Contract // This is the contract class you created above

03class MagicActivity: AppCompatActivity() {

05    lateinit var magic: Magic

06    lateinit var web3j: Web3j

08    // After user is successfully authenticated

09    private var account: String? = null

11    override fun onCreate(savedInstanceState: Bundle?) {

12        super.onCreate(savedInstanceState)

13        magic = (applicationContext as MagicDemoApp).magic

14        web3j = Web3j.build(magic.rpcProvider)

15    }

17    fun deployContract(view: View) {

18        try {

19            val price = BigInteger.valueOf(22000000000L)

20            val limit = BigInteger.valueOf(4300000)

21            val gasProvider = StaticGasProvider(price, limit)

22            val contract = Contract.deploy(

23                    web3j,

24                    account?.let { MagicTxnManager(web3j, it) },

25                    gasProvider,

26                    "HELLO_WORLD_FROM_ANDROID"

27            ).send()

28            Log.d("Magic", "Deploy to" + contract.contractAddress)

29        } catch (e: Exception) {

30            Log.e("E", "error", e)

31        }

32    }

33}

#Read From Contract

Kotlin

01fun contractRead(view: View) {

02    try {

03        val price = BigInteger.valueOf(22000000000L)

04        val limit = BigInteger.valueOf(4300000)

05        val gasProvider = StaticGasProvider(price, limit)

07        // Contract in testnet

08        val contract = ExampleContract.load("0x6a2d321a3679b1b3c8a19b84e41abd11763a8ab5", web3j, account?.let { MagicTxnManager(web3j, it) }, gasProvider)

09        if (contract.isValid) {

10            val ethCall = contract.message().send()

11            Log.d("Magic", ethCall.toString())

12        } else {

13            throw Error("contract not valid")

14        }

15    } catch (e: Exception) {

16        Log.e("E", "error", e)

17    }

18}

#Write to Contract

Kotlin

01fun contractWrite(view: View) {

02    try {

03        val price = BigInteger.valueOf(22000000000L)

04        val limit = BigInteger.valueOf(4300000)

05        val gasProvider = StaticGasProvider(price, limit)

07        // Contract in testnet

08        val contract = ExampleContract.load("0x6a2d321a3679b1b3c8a19b84e41abd11763a8ab5", web3j, account?.let { MagicTxnManager(web3j, it) }, gasProvider)

09        if (contract.isValid) {

10            val ethCall = contract.update("NEW_MESSAGE_FROM_ANDROID").send()

11            Log.d("Magic", ethCall.toString())

12        } else {

13            throw Error("contract not valid")

14        }

15    } catch (e: Exception) {

16        Log.e("E", "error", e)

17    }

18}

#Resources

Magic Android SDK

How to Integrate with the Ethereum Blockchain using Android

How to Integrate with the Ethereum Blockchain using Android

#Installation

#Initialization

#Use Different Networks

#Testnet

#Custom Node

#Associated Class

#Common Methods

#Send Transaction

#Sign Message

#Personal Sign

#Sign TypedData Legacy (V1)

#Sign Typed Data v3

#Sign Typed Data v4

#Get User Info

#Smart Contract

#Create a Kotlin/Java Contract Class from ABI

#Install web3j cli-tool

#Create the contract class

#Deploy Contract

#Read From Contract

#Write to Contract

#Resources

How to Integrate with the Ethereum Blockchain using iOS

How to Integrate with the Ethereum Blockchain using Unity

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