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Use MetaMask SDK with Android

Import MetaMask SDK into your native Android dapp to enable your users to easily connect with their MetaMask Mobile wallet.

See also

Prerequisites​

  • MetaMask Mobile version 7.6.0 or later installed on your target device (that is, a physical device or emulator). You can install MetaMask Mobile from Google Play, or clone and compile MetaMask Mobile from source and build to your target device.

  • Android SDK version 23 or later.

Steps​

1. Install the SDK​

To add the SDK from Maven Central as a dependency to your project, in your app/build.gradle file, add the following entry to the dependencies block:

build.gradle
dependencies {
  implementation "io.metamask.androidsdk:metamask-android-sdk"
}

Then, sync your project with the Gradle settings. Once the syncing completes, you can set up the rest of your project.

2. Import the SDK​

Import the SDK by adding the following line to the top of your project file:

import io.metamask.androidsdk.Ethereum

3. Connect your dapp​

The SDK supports callbacks using the Ethereum provider object, and coroutines using the EthereumFlow provider object. You can connect your dapp to MetaMask in one of two ways:

  1. Use the Ethereum or EthereumFlow provider object directly. We recommend using this method in a pure model layer.
  2. Use a ViewModel that injects the Ethereum or EthereumFlow provider object. We recommend using this method at the app level, because it provides a single instance that survives configuration changes and can be shared across all views.
Logging

By default, MetaMask logs three SDK events: connection_request, connected, and disconnected. This allows MetaMask to monitor any SDK connection issues. To disable this, set ethereum.enableDebug = false.

3.1. Use the provider object directly​

Use the Ethereum provider object (for callbacks) or the EthereumFlow provider object (for coroutines) to connect your dapp to MetaMask. Add the following code to your project file:

@AndroidEntryPoint
class SomeModel(context: Context) {

  val dappMetadata = DappMetadata("Droid Dapp", "https://www.droiddapp.io")

  // To use the Infura API to make read-only requests, specify your Infura API key using the
  // infuraAPIKey option in SDKOptions.
  val infuraAPIKey = "1234567890"

  // To use your own node (for example, with Hardhat) to make read-only requests, specify your
  // node's chain ID and RPC URL using the readonlyRPCMap option in SDKOptions.
  val readonlyRPCMap = mapOf("0x1" to "hptts://www.testrpc.com")

  // Use callbacks.
  val ethereum = Ethereum(context, dappMetadata, SDKOptions(infuraAPIKey, readonlyRPCMap))

  // This is the same as calling eth_requestAccounts.
  ethereum.connect() { result ->
    when (result) {
      is Result.Error -> {
        Logger.log("Ethereum connection error: ${result.error.message}")
      }
      is Result.Success.Item -> {
        Logger.log("Ethereum connection result: ${result.value}")
      }
    }
  }
}

As an alternative to calling the connect() method, you can call convenience methods to connect to MetaMask and make a request in a single RPC request.

3.2. Use a ViewModel​

To connect your dapp to MetaMask using a ViewModel, create a ViewModel that injects the Ethereum provider object (for callbacks) or the EthereumFlow provider object (for coroutines). Add wrapper functions for each Ethereum method you wish to call.

You can use a dependency manager such as Hilt to initialize the ViewModel and maintain its state across configuration changes. If you use Hilt, your setup might look like the following:

EthereumViewModel.kt
@HiltViewModel
class EthereumViewModel @Inject constructor(
  private val ethereum: Ethereum
): ViewModel() {

  val ethereumState = MediatorLiveData<EthereumState>().apply {
    addSource(ethereum.ethereumState) { newEthereumState ->
      value = newEthereumState
    }
  }

  // Wrapper function to connect the dapp.
  fun connect(callback: ((Result) -> Unit)?) {
    ethereum.connect(callback)
  }

  // Wrapper function call all RPC methods.
  fun sendRequest(request: EthereumRequest, callback: ((Result) -> Unit)?) {
    ethereum.sendRequest(request, callback)
  }
}

To use the ViewModel, add the following code to your project file:

val ethereumViewModel: EthereumFlowViewModel by viewModels()

// This is the same as calling eth_requestAccounts.
ethereumViewModel.connect()

As an alternative to calling the connect() method, you can call convenience methods to connect to MetaMask and make a request in a single RPC request.

info

See the example dapp's EthereumViewModel.kt and EthereumFlowViewModel.kt files for more information.

4. Call methods​

You can now call any JSON-RPC API method using ethereum.sendRequest(). The SDK also provides convenience methods for common RPC requests so you don't have to manually construct requests.

The following examples use coroutines.

Example: Get account balance​

The following example gets the user's account balance by calling eth_getBalance. This is a read-only request, which uses the Infura API if an infuraAPIKey is provided in the SDKOptions. We highly recommend using the Infura API to provide a seamless user experience.

val balance = ethereum.getEthBalance(ethereum.selectedAddress, "latest")

when (balance) {
  is Result.Success.Item -> {
    Logger.log("Ethereum account balance: ${result.value}")
    balance = result.value
  }
  is Result.Error -> {
    Logger.log("Ethereum request balance error: ${result.error.message}")
  }
}

Example: Sign message​

The following example requests the user sign a message by calling eth_signTypedData_v4.

val message = "{\"domain\":{\"chainId\":\"${ethereum.chainId}\",\"name\":\"Ether Mail\",\"verifyingContract\":\"0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC\",\"version\":\"1\"},\"message\":{\"contents\":\"Hello, Busa!\",\"from\":{\"name\":\"Kinno\",\"wallets\":[\"0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826\",\"0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF\"]},\"to\":[{\"name\":\"Busa\",\"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[]\"}]}}"
val address = ethereum.selectedAddress

when (val result = ethereum.ethSignTypedDataV4(message, address)) {
  is Result.Error -> {
    Logger.log("Ethereum sign error: ${result.error.message}")
  }
  is Result.Success.Item -> {
    Logger.log("Ethereum sign result: ${result.value}")
  }
}

Example: Batch requests​

The following example requests the user to sign a batch of messages by calling personal_sign and sendRequestBatch.

val ethereumRequest1 = EthereumRequest(
  method = EthereumMethod.PERSONAL_SIGN.value,
  params = listOf(address, "hello world")
)

val ethereumRequest2 = EthereumRequest(
  method = EthereumMethod.PERSONAL_SIGN.value,
  params = listOf(address, "second message")
)

when (val result = ethereum.sendRequestBatch(listOf(ethereumRequest1, ethereumRequest2))) {
  is Result.Error -> {
    Logger.log("Ethereum batch sign error: ${result.error.message}")
  }
  is Result.Success.Items -> {
    Logger.log("Ethereum batch sign result: ${result.value}")
  }
}

Example: Send transaction​

The following example sends a transaction by calling eth_sendTransaction.

val from = ethereum.selectedAddress
val to = "0x0000000000000000000000000000000000000000"
val value = "0x8ac7230489e80000"

when (val result = ethereum.sendTransaction(from, to, value)) {
  is Result.Success.Item -> {
    Logger.log("Ethereum transaction result: ${result.value}")
    balance = result.value
  }
  is Result.Error -> {
    // Handle error.
  }
}

Example: Switch chain​

The following example switches to a new Ethereum chain by calling wallet_switchEthereumChain.

when(val result = ethereum.switchEthereumChain(chainId)) {
  is Result.Success.Item -> {
    // Successfully switched to chainId.
  }
  is Result.Error -> {
    // Handle error.
  }
}

5. (Optional) Call convenience methods​

The SDK provides the following convenience methods to simplify connecting to MetaMask and calling common RPC methods. These examples use coroutines.

Example: Connect and request​

The following example uses the connectWith convenience method to connect to MetaMask and call eth_sendTransaction in one RPC request.

val params: Map<String, Any> = mutableMapOf(
  "from" to "", // This will be populated with the selected address once connected.
  "to" to "0x0000000000000000000000000000000000000000",
  "value" to "0x8ac7230489e80000"
)

val sendTransactionRequest = EthereumRequest(
  method = EthereumMethod.ETH_SEND_TRANSACTION.value,
  params = listOf(params)
)

when (val result = ethereum.connectWith(sendTransactionRequest)) {
  is Result.Error -> {
    // Handle error.
  }
  is Result.Success.Item -> {
    // Transaction hash ${result.value}
  }
}

Example: Connect and sign​

The following example uses the connectSign convenience method to connect to MetaMask and call personal_sign in one RPC request. You do not need to construct the personal_sign request, you only need to provide the message to sign.

val message = "This is the message to sign."

when (val result = ethereum.connectSign(message)) {
  is Result.Error -> {
    Logger.log("Ethereum connectSign error: ${result.error.message}")
  }
  is Result.Success.Item -> {
    Logger.log("Ethereum connectSign result: ${result.value}")
  }
}

Example​

See the example Android dapp in the Android SDK GitHub repository for more information.