Verify Paystack Payments in Android with Kotlin

// viewmodel/PaymentViewModel.kt
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

sealed class VerifyState {
    object Loading : VerifyState()
    data class Success(val amount: Double, val currency: String, val reference: String) : VerifyState()
    data class Failure(val message: String) : VerifyState()
}

class PaymentViewModel : ViewModel() {
    private val _verifyState = MutableStateFlow<VerifyState>(VerifyState.Loading)
    val verifyState: StateFlow<VerifyState> = _verifyState

    fun verifyPayment(reference: String) {
        viewModelScope.launch {
            _verifyState.value = VerifyState.Loading
            try {
                val result = RetrofitClient.paymentApi.verify(reference)
                if (result.verified) {
                    _verifyState.value = VerifyState.Success(
                        amount = result.amount ?: 0.0,
                        currency = result.currency ?: "NGN",
                        reference = result.reference ?: reference
                    )
                } else {
                    _verifyState.value = VerifyState.Failure("Payment not confirmed")
                }
            } catch (e: Exception) {
                _verifyState.value = VerifyState.Failure(
                    e.message ?: "Network error. Check your connection."
                )
            }
        }
    }
}

// PaymentResultActivity.kt
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.ProgressBar
import android.widget.TextView
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import kotlinx.coroutines.launch

class PaymentResultActivity : AppCompatActivity() {
    private val viewModel: PaymentViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_payment_result)

        val reference = intent.getStringExtra("reference") ?: return finish()

        val progressBar = findViewById<ProgressBar>(R.id.progressBar)
        val statusText = findViewById<TextView>(R.id.statusText)
        val retryButton = findViewById<Button>(R.id.retryButton)

        retryButton.setOnClickListener { viewModel.verifyPayment(reference) }

        lifecycleScope.launch {
            viewModel.verifyState.collect { state ->
                when (state) {
                    is VerifyState.Loading -> {
                        progressBar.visibility = View.VISIBLE
                        statusText.text = "Verifying payment..."
                        retryButton.visibility = View.GONE
                    }
                    is VerifyState.Success -> {
                        progressBar.visibility = View.GONE
                        statusText.text = "Payment confirmed!
${state.currency} ${state.amount}"
                        retryButton.visibility = View.GONE
                    }
                    is VerifyState.Failure -> {
                        progressBar.visibility = View.GONE
                        statusText.text = state.message
                        retryButton.visibility = View.VISIBLE
                    }
                }
            }
        }

        viewModel.verifyPayment(reference)
    }
}

This guide is part of the Paystack integration guides by language and framework series.

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