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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.

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 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 multiple messages at once by batching multiple requests that call personal_sign.

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.