Prepare UseCase3 for exercise about flow exception handling

Author: LukasLechnerDev

app/src/main/AndroidManifest.xml

@@ -103,6 +103,10 @@
             android:name=".usecases.flow.usecase2.FlowUseCase2Activity"
             android:exported="true" />
 
+        <activity
+            android:name=".usecases.flow.usecase3.FlowUseCase3Activity"
+            android:exported="true" />
+
     </application>
 
 </manifest>

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/base/UseCase.kt

@@ -25,6 +25,7 @@ import com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase8.
 import com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase9.DebuggingCoroutinesActivity
 import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase1.FlowUseCase1Activity
 import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase2.FlowUseCase2Activity
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3.FlowUseCase3Activity
 import kotlinx.parcelize.Parcelize
 
 @Parcelize
@@ -150,6 +151,7 @@ private val coroutinesUseCases =
 
 const val flowUseCase1Description = "#1 Flow Basics"
 const val flowUseCase2Description = "#2 Basic Intermediate operators"
+const val flowUseCase3Description = "#3 Exception Handling"
 
 private val flowUseCases =
     UseCaseCategory(
@@ -161,6 +163,9 @@ private val flowUseCases =
             ),UseCase(
                 flowUseCase2Description,
                 FlowUseCase2Activity::class.java
+            ),UseCase(
+                flowUseCase3Description,
+                FlowUseCase3Activity::class.java
             )
         )
     )

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase2/FlowUseCase2ViewModel.kt

@@ -69,5 +69,9 @@ class FlowUseCase2ViewModel(
         .onStart {
             emit(UiState.Loading)
         }
+        .catch { throwable ->
+            Timber.tag("Flow").d("Handle exception in catch operator $throwable")
+            emit(UiState.Error("Something went wrong..."))
+        }
         .asLiveData(defaultDispatcher)
 }

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase2/MockApiBehavior.kt

@@ -13,7 +13,6 @@ fun mockApi(context: Context) =
                 path = "/current-stock-prices",
                 body = { Gson().toJson(fakeCurrentStockPrices(context)) },
                 status = 200,
-                delayInMs = 1500,
-                errorFrequencyInPercent = 50
+                delayInMs = 1500
             )
     )

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase2/StockPriceDataSource.kt

@@ -5,6 +5,8 @@ import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.Stock
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.flow.retry
+import retrofit2.HttpException
 import timber.log.Timber
 
 interface StockPriceDataSource {
@@ -20,5 +22,14 @@ class NetworkStockPriceDataSource(mockApi: FlowMockApi) : StockPriceDataSource {
             emit(currentStockList)
             delay(5_000)
         }
+    }.retry { cause ->
+        Timber.tag("Flow").d("Enter retry operator with $cause")
+        val shouldRetry = cause is HttpException
+
+        if (shouldRetry) {
+            delay(5_000)
+        }
+
+        shouldRetry
     }
 }

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase3/FlowUseCase3Activity.kt

@@ -0,0 +1,56 @@
+package com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3
+
+import android.os.Bundle
+import androidx.activity.viewModels
+import com.lukaslechner.coroutineusecasesonandroid.base.BaseActivity
+import com.lukaslechner.coroutineusecasesonandroid.base.flowUseCase3Description
+import com.lukaslechner.coroutineusecasesonandroid.databinding.ActivityFlowUsecase1Binding
+import com.lukaslechner.coroutineusecasesonandroid.utils.setGone
+import com.lukaslechner.coroutineusecasesonandroid.utils.setVisible
+import com.lukaslechner.coroutineusecasesonandroid.utils.toast
+import org.joda.time.LocalDateTime
+import org.joda.time.format.DateTimeFormat
+
+class FlowUseCase3Activity : BaseActivity() {
+
+    private val binding by lazy { ActivityFlowUsecase1Binding.inflate(layoutInflater) }
+    private val adapter = StockAdapter()
+
+    private val viewModel: FlowUseCase3ViewModel by viewModels {
+        ViewModelFactory(NetworkStockPriceDataSource(mockApi(applicationContext)))
+    }
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(binding.root)
+        binding.recyclerView.adapter = adapter
+
+        viewModel.currentStockPriceAsLiveData.observe(this) { uiState ->
+            if (uiState != null) {
+                render(uiState)
+            }
+        }
+    }
+
+    private fun render(uiState: UiState) {
+        when (uiState) {
+            is UiState.Loading -> {
+                binding.progressBar.setVisible()
+                binding.recyclerView.setGone()
+            }
+            is UiState.Success -> {
+                binding.recyclerView.setVisible()
+                binding.lastUpdateTime.text =
+                    "lastUpdateTime: ${LocalDateTime.now().toString(DateTimeFormat.fullTime())}"
+                adapter.stockList = uiState.stockList
+                binding.progressBar.setGone()
+            }
+            is UiState.Error -> {
+                toast(uiState.message)
+                binding.progressBar.setGone()
+            }
+        }
+    }
+
+    override fun getToolbarTitle() = flowUseCase3Description
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase3/FlowUseCase3ViewModel.kt

@@ -0,0 +1,41 @@
+package com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.asLiveData
+import com.lukaslechner.coroutineusecasesonandroid.base.BaseViewModel
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.onCompletion
+import kotlinx.coroutines.flow.onStart
+import timber.log.Timber
+
+class FlowUseCase3ViewModel(
+    stockPriceDataSource: StockPriceDataSource
+) : BaseViewModel<UiState>() {
+
+    /*
+        Exercise: Flow Exception Handling
+
+        Tasks:
+        - Adjust code in StockPriceDataSource and FlowUseCase3ViewModel
+
+        Exception Handling Goals:
+        - for HttpExceptions in the datasource
+            - re-collect from the flow
+            - delay for 5 seconds before re-collecting the flow
+        - for all other Exceptions within the whole flow pipeline
+            - show toast with error message by emitting UiState.Error
+     */
+
+    val currentStockPriceAsLiveData: LiveData<UiState> = stockPriceDataSource
+        .latestStockList
+        .map { stockList ->
+            UiState.Success(stockList) as UiState
+        }
+        .onStart {
+            emit(UiState.Loading)
+        }
+        .onCompletion {
+            Timber.tag("Flow").d("Flow has completed.")
+        }
+        .asLiveData()
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase3/MockApiBehavior.kt

@@ -0,0 +1,19 @@
+package com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3
+
+import android.content.Context
+import com.google.gson.Gson
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.createFlowMockApi
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.fakeCurrentStockPrices
+import com.lukaslechner.coroutineusecasesonandroid.utils.MockNetworkInterceptor
+
+fun mockApi(context: Context) =
+    createFlowMockApi(
+        MockNetworkInterceptor()
+            .mock(
+                path = "/current-stock-prices",
+                body = { Gson().toJson(fakeCurrentStockPrices(context)) },
+                status = 200,
+                delayInMs = 1500,
+                errorFrequencyInPercent = 50
+            )
+    )

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase3/StockAdapter.kt

@@ -0,0 +1,43 @@
+package com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3
+
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.recyclerview.widget.RecyclerView
+import com.lukaslechner.coroutineusecasesonandroid.R
+import com.lukaslechner.coroutineusecasesonandroid.databinding.RecyclerviewItemStockBinding
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.Stock
+import java.text.NumberFormat
+
+class StockAdapter: RecyclerView.Adapter<StockAdapter.ViewHolder>() {
+
+    var stockList: List<Stock>? = null
+    set(value) {
+        field = value
+        notifyDataSetChanged()
+    }
+
+    private val formatter: NumberFormat = NumberFormat.getCurrencyInstance()
+
+    class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
+        val binding = RecyclerviewItemStockBinding.bind(view)
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
+        val view = LayoutInflater.from(parent.context).inflate(R.layout.recyclerview_item_stock, parent, false)
+        return ViewHolder(view)
+    }
+
+    override fun onBindViewHolder(holder: ViewHolder, position: Int) = with(holder.binding){
+        val stock = stockList?.get(position) ?: return@with
+        rank.text = stock.rank.toString()
+        name.text = stock.name
+        val currentPriceFormatted: String = formatter.format(stock.currentPrice)
+        currentPrice.text = currentPriceFormatted
+    }
+
+    override fun getItemCount(): Int {
+        return stockList?.size ?: 0
+    }
+
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/flow/usecase3/StockPriceDataSource.kt

@@ -0,0 +1,24 @@
+package com.lukaslechner.coroutineusecasesonandroid.usecases.flow.usecase3
+
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.FlowMockApi
+import com.lukaslechner.coroutineusecasesonandroid.usecases.flow.mock.Stock
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.flow
+import timber.log.Timber
+
+interface StockPriceDataSource {
+    val latestStockList: Flow<List<Stock>>
+}
+
+class NetworkStockPriceDataSource(mockApi: FlowMockApi) : StockPriceDataSource {
+
+    override val latestStockList: Flow<List<Stock>> = flow {
+        while (true) {
+            Timber.tag("Flow").d("Fetching current stock prices")
+            val currentStockList = mockApi.getCurrentStockPrices()
+            emit(currentStockList)
+            delay(5_000)
+        }
+    }
+}