Kotlin SDK Quickstart

This guide will walk you through the process of setting up Kaptos, fetching data, and sending a transaction on the Aptos blockchain.

Install the SDK

Kaptos is available for both multiplatform and single-platform development. Artifacts are published at Sonatype Maven Central and can be added to your project using Gradle as shown below:

Multiplatform Development

In your build.gradle.kts file, and in your commonMain source set block, add as follows:

kotlin {
    sourceSets {
        commonMain.dependencies {
            implementation("xyz.mcxross.kaptos:kaptos:<version>")
        }
    }
}

Single-platform Development

Depending on your target platform, Kaptos provides different artifacts in the form of kaptos-jvm, kaptos-android, kaptos-iosArm64, and kaptos-js. For example, to add the JVM artifact to your project, add the following dependency:

dependencies {
    implementation("xyz.mcxross.kaptos:kaptos-jvm:<version>")
}

To add the Android artifact, use:

dependencies {
    implementation("xyz.mcxross.kaptos:kaptos-android:<version>")
}

Set up the `Aptos` client

You can use the Aptos object to handle everything that requires a connection to the Aptos network.

val aptos = Aptos()

If you want to pass in a custom configuration, you can do so by passing in a AptosConfig object that takes in an AptosSettings object. The AptosSettings object allows you to specify the network you want to connect to, the fullnode URL, and other settings.

val settings = AptosSettings(network = Network.MAINNET, clientConfig = ClientConfig(maxRetries = 10))
val aptosConfig = AptosConfig(settings = settings)
val aptos = Aptos(aptosConfig)

ℹ️

Kaptos offers common configurations for all platforms while also providing platform-specific settings. For instance, you can configure both connection and request timeouts on Linux, whereas on iOS, you can only set request timeouts.

Fetch data from on-chain

Once you have an Aptos object, you can use it to fetch data from the Aptos blockchain. For example, you can fetch the ledger information like so:

val ledgerInfo = aptos.getLedgerInfo()

Send Transactions

To interact with the ledger and change its state, you must send transactions. To do this, you need an existing account. You can create an account by generating a new account key pair and funding the account on-chain. Once you have an account, you can sign transactions to demonstrate authority, allowing you to perform actions such as transferring tokens, triggering Move modules, or trading NFTs.

Here’s how you can build a transaction to transfer APT:

Create an Account

To create a new account, you first generate new credentials then fund the account. On test networks, you can fund an account programmatically by asking a “faucet”

val aliceAccount = Account.generate()
val bobAccount = Account.generate()

Build the Transaction

val txn = aptos.buildTransaction.simple(
    sender = aliceAccount.accountAddress,
    data = inputEntryFunctionData {
        function = "0x1::coin::transfer"
        typeArguments = typeArguments {
            +TypeTagStruct(type = "0x1::aptos_coin::AptosCoin".toStructTag())
        }
        functionArguments = functionArguments {
            +MoveString(bobAccount.accountAddress)
            +U64(SEND_AMOUNT)
        }
},)

Sign the Transaction

Once you have built a transaction, you can sign it using the sign method.

  val aliceAuthenticator = aptos.sign(
      sender = aliceAccount,
      transaction = txn,
  )

Submit the Transaction

Finally, you can submit the transaction to the network using the submitTransaction.simple method.

val commitedTransaction = aptos.submitTransaction.simple(
      transaction = signedTransaction,
      senderAuthenticator = aliceAuthenticator,
)

Wait for the Transaction to Execute

Then you can wait for the transaction to be executed by using the waitForTransaction method.

val executedTransaction = aptos.waitForTransaction(HexInput.fromString(commitedTransaction.expect("Transaction failed").hash))

Kotlin SDK Fetch Data via the Kotlin SDK