Tugas 6 - Currency Converter
Currency Converter
MainActivity.kt
package com.example.currencyconverter
import android.os.Bundle
import android.util.Log
import android.view.View
import android.widget.AdapterView
import android.widget.ArrayAdapter
import android.widget.Spinner
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.isVisible
import androidx.lifecycle.lifecycleScope
import com.example.currencyconverter.databinding.ActivityMainBinding
import kotlinx.coroutines.launch
import retrofit2.HttpException
import java.io.IOException
import java.text.NumberFormat
import java.util.Locale // For formatting currency
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
private var exchangeRates: Map<String, Double> = emptyMap()
private var currencyCodes: List<String> = emptyList()
private var lastUpdated: String? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
setupSpinners() // Initial setup (empty for now)
fetchExchangeRates()
binding.btnConvert.setOnClickListener {
performConversion()
}
}
private fun setupSpinners() {
// Create dummy adapters initially, they will be updated when data arrives
val dummyAdapter = ArrayAdapter(this, android.R.layout.simple_spinner_item, listOf("Loading..."))
dummyAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
binding.spinnerFromCurrency.adapter = dummyAdapter
binding.spinnerToCurrency.adapter = dummyAdapter
}
private fun updateSpinners() {
if (currencyCodes.isNotEmpty()) {
val adapter = ArrayAdapter(this, android.R.layout.simple_spinner_item, currencyCodes)
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
binding.spinnerFromCurrency.adapter = adapter
binding.spinnerToCurrency.adapter = adapter
val defaultFrom = "USD"
val defaultTo = "EUR"
val fromPosition = currencyCodes.indexOf(defaultFrom)
val toPosition = currencyCodes.indexOf(defaultTo)
if (fromPosition != -1) {
binding.spinnerFromCurrency.setSelection(fromPosition)
}
if (toPosition != -1) {
binding.spinnerToCurrency.setSelection(toPosition)
} else if (currencyCodes.isNotEmpty()) {
// Fallback to the first currency if the default 'to' is not found
binding.spinnerToCurrency.setSelection(0)
}
} else {
Log.e("MainActivity", "Currency codes list is empty.")
Toast.makeText(this, "Could not load currency list", Toast.LENGTH_SHORT).show()
}
}
private fun fetchExchangeRates() {
binding.progressBar.visibility = View.VISIBLE // Show progress bar
binding.btnConvert.isEnabled = false // Disable button while loading
// Use lifecycleScope for coroutine tied to Activity lifecycle
lifecycleScope.launch {
try {
val response = RetrofitInstance.api.getLatestRates()
if (response.isSuccessful && response.body() != null) {
val apiResponse = response.body()!!
if (apiResponse.result == "success") {
exchangeRates = apiResponse.rates
currencyCodes = exchangeRates.keys.toList().sorted() // Get and sort currency codes
lastUpdated = apiResponse.lastUpdateUtc
Log.d("MainActivity", "Rates fetched successfully: ${exchangeRates.size} currencies")
updateSpinners() // Update spinners with fetched data
updateLastUpdatedTimestamp()
} else {
showError("API returned an error: ${apiResponse.result}")
}
} else {
showError("Failed to fetch rates. Code: ${response.code()}")
}
} catch (e: IOException) {
// Network error (no internet, server unreachable)
Log.e("MainActivity", "Network error: ${e.message}", e)
showError("Network error. Please check your connection.")
} catch (e: HttpException) {
// HTTP error (4xx, 5xx)
Log.e("MainActivity", "HTTP error: ${e.message}", e)
showError("Could not retrieve data from server.")
} catch (e: Exception) {
// Other errors (parsing, etc.)
Log.e("MainActivity", "Error fetching rates: ${e.message}", e)
showError("An unexpected error occurred.")
} finally {
binding.progressBar.visibility = View.GONE // Hide progress bar
binding.btnConvert.isEnabled = true // Re-enable button
}
}
}
private fun updateLastUpdatedTimestamp() {
if (lastUpdated != null) {
binding.tvLastUpdated.text = "Last Updated: $lastUpdated"
binding.tvLastUpdated.visibility = View.VISIBLE
} else {
binding.tvLastUpdated.visibility = View.GONE
}
}
private fun performConversion() {
val amountString = binding.etAmount.text.toString()
val fromCurrency = binding.spinnerFromCurrency.selectedItem as? String
val toCurrency = binding.spinnerToCurrency.selectedItem as? String
if (amountString.isBlank()) {
binding.etAmount.error = "Please enter an amount"
return
}
binding.etAmount.error = null // Clear error
val amount = amountString.toDoubleOrNull()
if (amount == null || amount <= 0) {
binding.etAmount.error = "Please enter a valid positive amount"
return
}
binding.etAmount.error = null // Clear error
if (fromCurrency == null || toCurrency == null || exchangeRates.isEmpty()) {
showError("Currency data not loaded yet. Please wait or check connection.")
// Optionally, try fetching rates again here
// fetchExchangeRates()
return
}
// --- Conversion Logic ---
// The API provides rates relative to USD (the base_code in the example).
// Formula: amountInTarget = (amountInBase / rateOfSource) * rateOfTarget
// Since our base is USD:
// amountInUSD = amount / rateOfFromCurrency (relative to USD)
// result = amountInUSD * rateOfToCurrency (relative to USD)
// Simplified: result = amount * (rateOfToCurrency / rateOfFromCurrency)
val rateFrom = exchangeRates[fromCurrency]
val rateTo = exchangeRates[toCurrency]
if (rateFrom == null || rateTo == null || rateFrom == 0.0) {
Log.e("MainActivity", "Rate not found for $fromCurrency or $toCurrency or fromRate is zero.")
showError("Could not find exchange rate for the selected currencies.")
return
}
val resultValue = amount * (rateTo / rateFrom)
// Format the result nicely
val numberFormat = NumberFormat.getNumberInstance(Locale.getDefault()) // Use default locale formatting
numberFormat.maximumFractionDigits = 2 // Show up to 2 decimal places
val formattedResult = numberFormat.format(resultValue)
binding.tvResult.text = "$formattedResult $toCurrency"
binding.tvResult.visibility = View.VISIBLE
}
private fun showError(message: String) {
Toast.makeText(this, message, Toast.LENGTH_LONG).show()
binding.tvResult.text = "" // Clear previous result on error
binding.tvResult.visibility = View.INVISIBLE
}
}
ApiResponse.kt
package com.example.currencyconverter
import com.google.gson.annotations.SerializedName
// Represents the entire API response
data class ApiResponse(
@SerializedName("result") val result: String,
@SerializedName("base_code") val baseCode: String,
@SerializedName("rates") val rates: Map<String, Double>,
@SerializedName("time_last_update_utc") val lastUpdateUtc: String? = null
)
ExchangeRateApiService.kt
package com.example.currencyconverter
import retrofit2.Response
import retrofit2.http.GET
import retrofit2.http.Path
interface ExchangeRateApiService {
@GET("v6/latest/USD")
suspend fun getLatestRates(): Response<ApiResponse>
@GET("v6/latest/{baseCurrency}")
suspend fun getRatesForBase(
@Path("baseCurrency") baseCurrency: String
): Response<ApiResponse>
}
RetrofitInstance.kt
package com.example.currencyconverter
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
object RetrofitInstance {
private const val BASE_URL = "https://open.er-api.com/"
val api: ExchangeRateApiService by lazy {
Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create()) // Use Gson for parsing
.build()
.create(ExchangeRateApiService::class.java)
}
}
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