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.

1. 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

   Section titled “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

   Section titled “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>")
   }

2. 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)

3. 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()

4. 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:

   1. Create an Account

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

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

      On testnet you can mint at the mint page.

   2. Build the Transaction

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

   3. 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,
        )

   4. Submit the Transaction

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

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

   5. 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(committedTransaction.expect("Transaction failed").hash))