add item detail with navigation from feed lists

app/build.gradle

@@ -3,6 +3,7 @@ apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-android-extensions'
 apply plugin: 'kotlinx-serialization'
 apply plugin: 'kotlin-kapt'
+apply plugin: "androidx.navigation.safeargs.kotlin"
 
 android {
     compileSdkVersion 29

app/src/main/java/com/sfjava/tunesfeed/ViewModelFactory.kt

@@ -6,7 +6,8 @@ import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.savedstate.SavedStateRegistryOwner
 import com.sfjava.tunesfeed.data.source.FeedItemsRepository
-import com.sfjava.tunesfeed.ui.feeds.FeedListViewModel
+import com.sfjava.tunesfeed.ui.feeditem.FeedItemViewModel
+import com.sfjava.tunesfeed.ui.feedlist.FeedListViewModel
 
 /**
  * Factory for all ViewModels.
@@ -26,6 +27,8 @@ class ViewModelFactory constructor(
         when {
             isAssignableFrom(FeedListViewModel::class.java) ->
                 FeedListViewModel(itemsRepository) //, handle) // FIXME: handle state persistence?
+//            isAssignableFrom(FeedItemViewModel::class.java) ->
+//                FeedItemViewModel(feedListViewModel) //, handle) // FIXME: handle state persistence?
             else ->
                 throw IllegalArgumentException("Unknown ViewModel class: ${modelClass.name}")
         }

app/src/main/java/com/sfjava/tunesfeed/ui/Event.kt

@@ -0,0 +1,44 @@
+package com.sfjava.tunesfeed.ui
+
+import androidx.lifecycle.Observer
+
+/**
+ * Used as a wrapper for data that is exposed via a LiveData that represents an event.
+ */
+open class Event<out T>(private val content: T) {
+
+    @Suppress("MemberVisibilityCanBePrivate")
+    var hasBeenHandled = false
+        private set // allow external read but not write
+
+    /**
+     * Returns the content and prevents its use again.
+     */
+    fun getContentIfNotHandled(): T? {
+        return if (hasBeenHandled) {
+            null
+        } else {
+            hasBeenHandled = true
+            content
+        }
+    }
+
+    /**
+     * Returns the content, even if it's already been handled.
+     */
+    fun peekContent(): T = content
+}
+
+/**
+ * An [Observer] for [Event]s, simplifying the pattern of checking if the [Event]'s content has
+ * already been handled.
+ *
+ * [onEventUnhandledContent] is *only* called if the [Event]'s contents has not been handled.
+ */
+class EventObserver<T>(private val onEventUnhandledContent: (T) -> Unit) : Observer<Event<T>> {
+    override fun onChanged(event: Event<T>?) {
+        event?.getContentIfNotHandled()?.let {
+            onEventUnhandledContent(it)
+        }
+    }
+}

app/src/main/java/com/sfjava/tunesfeed/ui/feeditem/FeedItemDetailFragment.kt

@@ -0,0 +1,39 @@
+package com.sfjava.tunesfeed.ui.feeditem
+
+import android.os.Bundle
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.viewModels
+import com.sfjava.tunesfeed.data.model.FeedType
+import com.sfjava.tunesfeed.databinding.FeedItemDetailFragmentBinding
+import com.sfjava.tunesfeed.ui.feeditem.FeedItemDetailFragmentArgs.Companion.fromBundle
+import com.sfjava.tunesfeed.ui.getViewModelFactory
+
+class FeedItemDetailFragment(): Fragment() {
+
+    private val itemId by lazy {
+        arguments?.let { fromBundle(it).itemId } ?: throw IllegalArgumentException("Expected arguments")
+    }
+
+    private val feedItemViewModel
+            by viewModels<FeedItemViewModel> { getViewModelFactory(FeedType.ComingSoon) } // FIXME
+
+    private lateinit var viewDataBinding: FeedItemDetailFragmentBinding
+
+    override fun onCreateView(
+        inflater: LayoutInflater,
+        container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        viewDataBinding = FeedItemDetailFragmentBinding.inflate(inflater, container, false).apply {
+            viewmodel = feedItemViewModel
+        }
+        return viewDataBinding.root
+    }
+
+    override fun onActivityCreated(savedInstanceState: Bundle?) {
+        super.onActivityCreated(savedInstanceState)
+    }
+}

app/src/main/java/com/sfjava/tunesfeed/ui/feeditem/FeedItemViewModel.kt

@@ -0,0 +1,15 @@
+package com.sfjava.tunesfeed.ui.feeditem
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+import androidx.lifecycle.ViewModel
+import com.sfjava.tunesfeed.data.model.FeedItem
+import com.sfjava.tunesfeed.ui.feedlist.FeedListViewModel
+
+class FeedItemViewModel(val feedListViewModel: FeedListViewModel): ViewModel() {
+
+    private val _item = MutableLiveData<FeedItem>()
+    val item: LiveData<FeedItem> = _item
+
+    fun getItem(id: String) = feedListViewModel.getItem(id)
+}

app/src/main/java/com/sfjava/tunesfeed/ui/feeds/FeedListAdapter.kt → app/src/main/java/com/sfjava/tunesfeed/ui/feedlist/FeedListAdapter.kt

@@ -1,4 +1,4 @@
-package com.sfjava.tunesfeed.ui.feeds
+package com.sfjava.tunesfeed.ui.feedlist
 
 import android.view.LayoutInflater
 import android.view.ViewGroup
@@ -24,7 +24,7 @@ class FeedListAdapter(private val viewModel: FeedListViewModel) :
         RecyclerView.ViewHolder(binding.root) {
 
         fun bind(viewModel: FeedListViewModel, item: FeedItem) {
-            // binding.viewmodel = viewModel // NOTE: plumb-through if we need to ref the list-model
+            binding.feedListViewModel = viewModel // NOTE: need to ref this for item on-click action
             binding.item = item
             binding.executePendingBindings()
         }

app/src/main/java/com/sfjava/tunesfeed/ui/feeds/FeedListBindings.kt → app/src/main/java/com/sfjava/tunesfeed/ui/feedlist/FeedListBindings.kt

@@ -1,4 +1,4 @@
-package com.sfjava.tunesfeed.ui.feeds
+package com.sfjava.tunesfeed.ui.feedlist
 
 import android.widget.ImageView
 import androidx.databinding.BindingAdapter

app/src/main/java/com/sfjava/tunesfeed/ui/feeds/FeedListFragment.kt → app/src/main/java/com/sfjava/tunesfeed/ui/feedlist/FeedListFragment.kt

@@ -1,4 +1,4 @@
-package com.sfjava.tunesfeed.ui.feeds
+package com.sfjava.tunesfeed.ui.feedlist
 
 import android.os.Bundle
 import android.util.Log
@@ -7,24 +7,26 @@ import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.viewModels
+import androidx.navigation.fragment.findNavController
 import com.sfjava.tunesfeed.data.model.FeedType
-import com.sfjava.tunesfeed.databinding.FragmentFeedListBinding
+import com.sfjava.tunesfeed.databinding.FeedListFragmentBinding
+import com.sfjava.tunesfeed.ui.EventObserver
 import com.sfjava.tunesfeed.ui.getViewModelFactory
 
 class FeedListFragment : Fragment() {
 
     private val feedListViewModel
             by viewModels<FeedListViewModel> { getViewModelFactory(arguments?.get("feedType") as FeedType) }
 
-    private lateinit var viewDataBinding: FragmentFeedListBinding
+    private lateinit var viewDataBinding: FeedListFragmentBinding
     private lateinit var listAdapter: FeedListAdapter
 
     override fun onCreateView(
             inflater: LayoutInflater,
             container: ViewGroup?,
             savedInstanceState: Bundle?
     ): View? {
-        viewDataBinding = FragmentFeedListBinding.inflate(inflater, container, false).apply {
+        viewDataBinding = FeedListFragmentBinding.inflate(inflater, container, false).apply {
             viewmodel = feedListViewModel
         }
         return viewDataBinding.root
@@ -33,13 +35,22 @@ class FeedListFragment : Fragment() {
     override fun onActivityCreated(savedInstanceState: Bundle?) {
         super.onActivityCreated(savedInstanceState)
 
-        viewDataBinding.lifecycleOwner = this.viewLifecycleOwner
+        viewDataBinding.lifecycleOwner = viewLifecycleOwner
         val viewModel = viewDataBinding.viewmodel
         if (viewModel != null) {
             listAdapter = FeedListAdapter(viewModel)
             viewDataBinding.itemsList.adapter = listAdapter
         } else {
             Log.w("TunesFeed", "ViewModel not initialized when attempting to set up adapter.")
         }
+
+        viewModel?.showItemDetailEvent?.observe(viewLifecycleOwner, EventObserver {
+            showItemDetail(it)
+        })
+    }
+
+    private fun showItemDetail(id: String) {
+        val action = FeedListFragmentDirections.actionFeedListFragmentToFeedItemDetailFragment(id)
+        findNavController().navigate(action)
     }
 }

app/src/main/java/com/sfjava/tunesfeed/ui/feeds/FeedListViewModel.kt → app/src/main/java/com/sfjava/tunesfeed/ui/feedlist/FeedListViewModel.kt

@@ -1,9 +1,10 @@
-package com.sfjava.tunesfeed.ui.feeds
+package com.sfjava.tunesfeed.ui.feedlist
 
 import androidx.lifecycle.*
 import com.sfjava.tunesfeed.data.model.FeedItem
 import com.sfjava.tunesfeed.data.source.FeedItemsRepository
 import com.sfjava.tunesfeed.data.source.Result
+import com.sfjava.tunesfeed.ui.Event
 import kotlinx.coroutines.launch
 
 class FeedListViewModel(val itemsRepository: FeedItemsRepository) : ViewModel() {
@@ -22,6 +23,9 @@ class FeedListViewModel(val itemsRepository: FeedItemsRepository) : ViewModel()
     }
     val items: LiveData<List<FeedItem>> = _items
 
+    private val _showItemDetailEvent = MutableLiveData<Event<String>>()
+    val showItemDetailEvent: LiveData<Event<String>> = _showItemDetailEvent
+
     private val _dataLoading = MutableLiveData<Boolean>()
     val dataLoading: LiveData<Boolean> = _dataLoading
 
@@ -39,6 +43,12 @@ class FeedListViewModel(val itemsRepository: FeedItemsRepository) : ViewModel()
         _forceUpdate.value = forceUpdate
     }
 
+    fun getItem(id: String): FeedItem? = _items.value?.filter { it.id == id }?.firstOrNull()
+
+    fun showItemDetail(id: String) {
+        _showItemDetailEvent.value = Event(id)
+    }
+
     private fun filterItems(itemsResult: Result<List<FeedItem>>): LiveData<List<FeedItem>> {
         // TODO: this is a good case for liveData builder; replace when stable (per google's sample)
         val result = MutableLiveData<List<FeedItem>>()

app/src/main/res/layout/activity_main.xml

@@ -27,6 +27,6 @@
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"
         app:layout_constraintTop_toTopOf="parent"
-        app:navGraph="@navigation/mobile_navigation" />
+        app:navGraph="@navigation/nav_graph" />
 
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/feed_item_detail_fragment.xml

@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
+
+    <data>
+        <variable
+            name="viewmodel"
+            type="com.sfjava.tunesfeed.ui.feeditem.FeedItemViewModel" />
+    </data>
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="?android:attr/listPreferredItemHeight"
+        android:orientation="horizontal"
+        android:paddingLeft="@dimen/activity_horizontal_margin"
+        android:paddingRight="@dimen/activity_horizontal_margin"
+        android:paddingBottom="4dp">
+
+        <ImageView
+            android:id="@+id/product_image"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:maxHeight="125dp"
+            android:scaleType="centerCrop"
+            android:adjustViewBounds ="true"
+            app:imageUrl="@{viewmodel.item.artworkUrl100}"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <LinearLayout
+            android:layout_width="wrap_content"
+            android:layout_height="match_parent"
+            android:orientation="vertical">
+
+            <TextView
+                android:id="@+id/title_text"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_gravity="top"
+                android:layout_marginStart="@dimen/activity_horizontal_margin"
+                android:layout_marginLeft="@dimen/activity_horizontal_margin"
+                android:text="@{viewmodel.item.name}"
+                android:textAppearance="@style/TextAppearance.AppCompat.Small" />
+
+            <TextView
+                android:id="@+id/title_text2"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_gravity="top"
+                android:layout_marginStart="@dimen/activity_horizontal_margin"
+                android:layout_marginLeft="@dimen/activity_horizontal_margin"
+                android:text="@{viewmodel.item.artistName}"
+                android:textStyle="bold"
+                android:textAppearance="@style/TextAppearance.AppCompat.Small" />
+
+        </LinearLayout>
+
+    </LinearLayout>
+</layout>

app/src/main/res/layout/fragment_feed_list.xml → app/src/main/res/layout/feed_list_fragment.xml

@@ -6,7 +6,7 @@
         <import type="android.view.View" />
         <variable
             name="viewmodel"
-            type="com.sfjava.tunesfeed.ui.feeds.FeedListViewModel" />
+            type="com.sfjava.tunesfeed.ui.feedlist.FeedListViewModel" />
     </data>
 
     <androidx.constraintlayout.widget.ConstraintLayout

app/src/main/res/layout/feed_item.xml → app/src/main/res/layout/feed_list_item.xml

@@ -6,6 +6,10 @@
         <variable
             name="item"
             type="com.sfjava.tunesfeed.data.model.FeedItem" />
+
+        <variable
+            name="feedListViewModel"
+            type="com.sfjava.tunesfeed.ui.feedlist.FeedListViewModel" />
     </data>
 
     <LinearLayout
@@ -14,8 +18,8 @@
         android:orientation="horizontal"
         android:paddingLeft="@dimen/activity_horizontal_margin"
         android:paddingRight="@dimen/activity_horizontal_margin"
-        android:paddingBottom="4dp">
-<!--    android:onClick="@{() -> viewmodel.openTask(task.id)}">-->
+        android:paddingBottom="4dp"
+        android:onClick="@{() -> feedListViewModel.showItemDetail(item.id)}">
 
         <ImageView
             android:id="@+id/product_image"