Add a proper error handling if user hit the convert button without en…

…tering any amount.

Add Navigation, NavigationGraph.kt that contains splash screen and also main currency rate listing screen for better management of UI.

Refactor MainNavigationActivity.kt name and its package.

app/src/main/AndroidManifest.xml

@@ -18,7 +18,7 @@
         tools:targetApi="31">
         <activity
             android:screenOrientation="portrait"
-            android:name=".ui.currencyrates.CurrencyRatesActivity"
+            android:name=".ui.MainNavigationActivity"
             android:exported="true"
             android:label="@string/app_name"
             android:theme="@style/Theme.CurrencyConverter">

app/src/main/java/com/asad/currencyconverter/ui/currencyrates/CurrencyRatesViewModel.kt → app/src/main/java/com/asad/currencyconverter/ui/MainActivityViewModel.kt

@@ -1,4 +1,4 @@
-package com.asad.currencyconverter.ui.currencyrates
+package com.asad.currencyconverter.ui
 
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
@@ -13,14 +13,21 @@ import kotlinx.coroutines.launch
 import javax.inject.Inject
 
 @HiltViewModel
-class CurrencyRatesViewModel @Inject constructor(private val repository: CurrencyRatesRepository) :
+class MainActivityViewModel @Inject constructor(private val repository: MainRepository) :
     ViewModel() {
 
     private val _uiState = MutableStateFlow<UiStates>(LoadingState)
     val uiState: StateFlow<UiStates> = _uiState
 
-    private val _currencyRatesList = MutableStateFlow<List<CurrencyRatesDbModel>>(arrayListOf())
-    val currencyRatesList: StateFlow<List<CurrencyRatesDbModel>> = _currencyRatesList
+    private val _originalCurrencyRatesList =
+        MutableStateFlow<List<CurrencyRatesDbModel>>(arrayListOf())
+    val originalCurrencyRatesList: StateFlow<List<CurrencyRatesDbModel>> =
+        _originalCurrencyRatesList
+
+    private val _conversionCurrencyRatesList =
+        MutableStateFlow<List<CurrencyRatesDbModel>>(arrayListOf())
+    val conversionCurrencyRatesList: StateFlow<List<CurrencyRatesDbModel>> =
+        _conversionCurrencyRatesList
 
     private val _selectedCurrency = MutableStateFlow(CurrencyRatesDbModel())
     val selectedCurrency: StateFlow<CurrencyRatesDbModel> = _selectedCurrency
@@ -33,8 +40,8 @@ class CurrencyRatesViewModel @Inject constructor(private val repository: Currenc
         repository.fetchCurrencyRatesFromDb().collect {
             if (it.isNotEmpty()) {
                 _uiState.value = ContentState
-                _currencyRatesList.value = it
-                _selectedCurrency.value = _currencyRatesList.value.first()
+                _originalCurrencyRatesList.value = it
+                _selectedCurrency.value = _originalCurrencyRatesList.value.first()
             } else {
                 if (CurrencyConverterApp.isNetworkConnected) {
                     _uiState.value = LoadingState
@@ -46,7 +53,7 @@ class CurrencyRatesViewModel @Inject constructor(private val repository: Currenc
     fun performConversion(amount: Double) {
         viewModelScope.launch(Dispatchers.Default) {
             val list: MutableList<CurrencyRatesDbModel> = ArrayList()
-            currencyRatesList.value.let { listItems ->
+            originalCurrencyRatesList.value.let { listItems ->
                 if (listItems.isNotEmpty()) {
                     val currencyValue = amount / listItems.filter {
                         selectedCurrency.value.currencyName == it.currencyName
@@ -65,7 +72,7 @@ class CurrencyRatesViewModel @Inject constructor(private val repository: Currenc
                 }
             }
 
-            _currencyRatesList.value = list
+            _conversionCurrencyRatesList.value = list
         }
 
     }

app/src/main/java/com/asad/currencyconverter/ui/MainNavigationActivity.kt

@@ -0,0 +1,19 @@
+package com.asad.currencyconverter.ui
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.viewModels
+import com.asad.currencyconverter.ui.navgraph.Navigation
+import dagger.hilt.android.AndroidEntryPoint
+
+@AndroidEntryPoint
+class MainNavigationActivity : ComponentActivity() {
+    private val viewModel: MainActivityViewModel by viewModels()
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContent {
+            Navigation(viewModel)
+        }
+    }
+}

app/src/main/java/com/asad/currencyconverter/ui/currencyrates/CurrencyRatesRepository.kt → app/src/main/java/com/asad/currencyconverter/ui/MainRepository.kt

@@ -1,9 +1,9 @@
-package com.asad.currencyconverter.ui.currencyrates
+package com.asad.currencyconverter.ui
 
 import com.asad.currencyconverter.data.manager.AppDataManager
 import javax.inject.Inject
 
-class CurrencyRatesRepository @Inject constructor(private val dataManager: AppDataManager) {
+class MainRepository @Inject constructor(private val dataManager: AppDataManager) {
 
     fun fetchCurrencyRatesFromDb() = dataManager.getAppDatabaseHelper().getCurrencyRatesList()
 

app/src/main/java/com/asad/currencyconverter/ui/currencyrates/UiStates.kt → app/src/main/java/com/asad/currencyconverter/ui/UiStates.kt

@@ -1,4 +1,4 @@
-package com.asad.currencyconverter.ui.currencyrates
+package com.asad.currencyconverter.ui
 
 
 sealed class UiStates

app/src/main/java/com/asad/currencyconverter/ui/currencyrates/CurrencyRates.kt

@@ -18,8 +18,13 @@ import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.material.CircularProgressIndicator
+import androidx.compose.material.Scaffold
+import androidx.compose.material.Snackbar
+import androidx.compose.material.SnackbarHost
+import androidx.compose.material.SnackbarHostState
 import androidx.compose.material.Surface
 import androidx.compose.material.Text
+import androidx.compose.material.TextButton
 import androidx.compose.material.TextField
 import androidx.compose.material.TextFieldDefaults
 import androidx.compose.runtime.*
@@ -39,60 +44,105 @@ import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.asad.currencyconverter.R
 import com.asad.currencyconverter.data.local.models.CurrencyRatesDbModel
+import com.asad.currencyconverter.ui.ContentState
+import com.asad.currencyconverter.ui.ErrorState
+import com.asad.currencyconverter.ui.LoadingState
+import com.asad.currencyconverter.ui.MainActivityViewModel
 import com.asad.currencyconverter.ui.theme.CurrencyConverterTheme
+import kotlinx.coroutines.launch
 
 @Composable
-fun CurrencyConverter(viewModel: CurrencyRatesViewModel = viewModel()) {
+fun CurrencyConverter(viewModel: MainActivityViewModel = viewModel()) {
     val uiState = viewModel.uiState.collectAsState()
-    val currencyRatesList = viewModel.currencyRatesList.collectAsState().value
+    val currencyRatesList = viewModel.originalCurrencyRatesList.collectAsState().value
+    val conversionCurrencyRatesList = viewModel.conversionCurrencyRatesList.collectAsState().value
     val selectedCurrency = viewModel.selectedCurrency.collectAsState().value
 
     var amount by rememberSaveable {
         mutableStateOf(0.toDouble())
     }
 
-    Column(modifier = Modifier.fillMaxSize()) {
-        HeaderSection(
-            modifier = Modifier.fillMaxWidth()
-        ) {
-            amount = it
-            viewModel.performConversion(amount)
-        }
+    val snackBarHostState = remember { SnackbarHostState() }
+    val coroutineScope = rememberCoroutineScope()
+    Scaffold(modifier = Modifier.fillMaxWidth(),
+        snackbarHost = {
+            SnackbarHost(
+                hostState = snackBarHostState,
+                snackbar = { data ->
+                    Snackbar(
+                        modifier = Modifier.padding(16.dp),
+                        content = { Text(data.message) },
+                        action = {
+                            data.actionLabel?.let { label ->
+                                TextButton(onClick = { data.performAction() }) {
+                                    Text(label)
+                                }
+                            }
+                        }
+                    )
+                }
+            )
+        },
+        topBar = {
+            HeaderSection(
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .background(color = Color.Black)
+            ) {
+                if (it.isNotEmpty()) {
+                    amount = it.toDouble()
+                    viewModel.performConversion(amount)
+                } else {
+                    coroutineScope.launch {
+                        snackBarHostState.showSnackbar("Please Enter amount")
+                    }
+                }
 
-        when (uiState.value) {
-            is LoadingState -> {
-                LoadingState(
-                    modifier = Modifier
-                        .fillMaxSize()
-                        .background(
-                            color = Color.White,
-                            shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
-                        )
-                )
             }
+        }
+    ) { innerPadding ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(innerPadding)
+        ) {
+            when (uiState.value) {
+                is LoadingState -> {
+                    LoadingState(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .background(
+                                color = Color.White,
+                                shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
+                            )
+                    )
+                }
 
-            is ContentState -> {
-                CurrenciesList(
-                    modifier = Modifier
-                        .fillMaxSize()
-                        .background(
-                            color = Color.White,
-                            shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
-                        ), selectedCurrency, currencyRatesList
-                ) { currencyRatesModel ->
-                    viewModel.updateSelectedCurrency(currencyRatesModel)
+                is ContentState -> {
+                    CurrenciesList(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .background(
+                                color = Color.White,
+                                shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
+                            ),
+                        selectedCurrency,
+                        conversionCurrencyRatesList.ifEmpty { currencyRatesList }
+                    ) { currencyRatesModel ->
+                        viewModel.updateSelectedCurrency(currencyRatesModel)
+                    }
                 }
-            }
 
-            is ErrorState -> {
-                ErrorState(
-                    modifier = Modifier
-                        .fillMaxSize()
-                        .background(
-                            color = Color.White,
-                            shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
-                        )
-                )
+                is ErrorState -> {
+                    ErrorState(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .background(
+                                color = Color.White,
+                                shape = RoundedCornerShape(topStart = 10.dp, topEnd = 10.dp)
+                            )
+                    )
+                }
             }
         }
 
@@ -207,7 +257,7 @@ fun ItemCurrencyPreview() {
 @OptIn(ExperimentalUnitApi::class)
 @Composable
 fun HeaderSection(
-    modifier: Modifier = Modifier, onAmountValueChange: (amount: Double) -> Unit
+    modifier: Modifier = Modifier, onAmountValueChange: (amount: String) -> Unit
 ) {
     var amount by rememberSaveable {
         mutableStateOf("")
@@ -248,7 +298,7 @@ fun HeaderSection(
                     color = Color.White,
                     fontSize = TextUnit(25f, TextUnitType.Sp),
                     modifier = Modifier.clickable {
-                        onAmountValueChange.invoke(amount.toDouble())
+                        onAmountValueChange.invoke(amount)
                     })
             },
             textStyle = TextStyle(fontSize = TextUnit(30f, TextUnitType.Sp)),

app/src/main/java/com/asad/currencyconverter/ui/navgraph/NavigationGraph.kt

@@ -0,0 +1,34 @@
+package com.asad.currencyconverter.ui.navgraph
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import com.asad.currencyconverter.ui.MainActivityViewModel
+import com.asad.currencyconverter.ui.currencyrates.CurrencyConverter
+import com.asad.currencyconverter.ui.splash.SplashScreen
+import kotlinx.coroutines.delay
+
+@Composable
+fun Navigation(viewModel: MainActivityViewModel) {
+    val navController = rememberNavController()
+
+    LaunchedEffect(Unit) {
+        delay(500)
+        navController.navigate(route = Screen.CurrencyRatesListScreen.route) {
+            popUpTo(Screen.SplashScreen.route) {
+                inclusive = true
+            }
+        }
+    }
+
+    NavHost(navController = navController, startDestination = Screen.SplashScreen.route) {
+        composable(Screen.SplashScreen.route) {
+            SplashScreen()
+        }
+        composable(route = Screen.CurrencyRatesListScreen.route) {
+            CurrencyConverter(viewModel)
+        }
+    }
+}

app/src/main/java/com/asad/currencyconverter/ui/navgraph/Screen.kt

@@ -0,0 +1,6 @@
+package com.asad.currencyconverter.ui.navgraph
+
+sealed class Screen(val route: String) {
+    object SplashScreen : Screen("SplashScreen")
+    object CurrencyRatesListScreen : Screen("CurrencyRatesListScreen")
+}

app/src/main/java/com/asad/currencyconverter/ui/splash/SplashScreen.kt

@@ -0,0 +1,26 @@
+package com.asad.currencyconverter.ui.splash
+
+import androidx.compose.foundation.Image
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.painterResource
+import com.asad.currencyconverter.R
+
+@Composable
+fun SplashScreen() {
+    Box(
+        modifier = Modifier
+            .fillMaxSize()
+            .background(color = Color.White),
+        contentAlignment = Alignment.Center
+    ) {
+        Image(
+            painter = painterResource(id = R.drawable.ic_currency), contentDescription = null,
+        )
+    }
+}

app/src/main/res/values/themes.xml

@@ -1,5 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <style name="Theme.CurrencyConverter" parent="android:Theme.Material.Light.NoActionBar" />
+    <style name="Theme.CurrencyConverter" parent="android:Theme.Material.Light.NoActionBar">
+        <item name="android:windowDisablePreview">true</item>
+    </style>
 </resources>