> { videos ->
+ videos?.apply {
+ viewModelAdapter?.videos = videos
+ }
+ })
+ }
+
+ /**
+ * Called to have the fragment instantiate its user interface view.
+ *
+ * If you return a View from here, you will later be called in
+ * {@link #onDestroyView} when the view is being released.
+ *
+ * @param inflater The LayoutInflater object that can be used to inflate
+ * any views in the fragment,
+ * @param container If non-null, this is the parent view that the fragment's
+ * UI should be attached to. The fragment should not add the view itself,
+ * but this can be used to generate the LayoutParams of the view.
+ * @param savedInstanceState If non-null, this fragment is being re-constructed
+ * from a previous saved state as given here.
+ *
+ * @return Return the View for the fragment's UI.
+ */
+ override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
+ savedInstanceState: Bundle?): View? {
+ val binding: FragmentDevByteBinding = DataBindingUtil.inflate(
+ inflater,
+ R.layout.fragment_dev_byte,
+ container,
+ false)
+ // Set the lifecycleOwner so DataBinding can observe LiveData
+ binding.setLifecycleOwner(viewLifecycleOwner)
+
+ binding.viewModel = viewModel
+
+ viewModelAdapter = DevByteAdapter(VideoClick {
+ // When a video is clicked this block or lambda will be called by DevByteAdapter
+
+ // context is not around, we can safely discard this click since the Fragment is no
+ // longer on the screen
+ val packageManager = context?.packageManager ?: return@VideoClick
+
+ // Try to generate a direct intent to the YouTube app
+ var intent = Intent(Intent.ACTION_VIEW, it.launchUri)
+ if(intent.resolveActivity(packageManager) == null) {
+ // YouTube app isn't found, use the web url
+ intent = Intent(Intent.ACTION_VIEW, Uri.parse(it.url))
+ }
+
+ startActivity(intent)
+ })
+
+ binding.root.findViewById(R.id.recycler_view).apply {
+ layoutManager = LinearLayoutManager(context)
+ adapter = viewModelAdapter
+ }
+
+
+ // Observer for the network error.
+ viewModel.eventNetworkError.observe(this, Observer { isNetworkError ->
+ if (isNetworkError) onNetworkError()
+ })
+
+ return binding.root
+ }
+
+ /**
+ * Method for displaying a Toast error message for network errors.
+ */
+ private fun onNetworkError() {
+ if(!viewModel.isNetworkErrorShown.value!!) {
+ Toast.makeText(activity, "Network Error", Toast.LENGTH_LONG).show()
+ viewModel.onNetworkErrorShown()
+ }
+ }
+
+ /**
+ * Helper method to generate YouTube app links
+ */
+ private val DevByteVideo.launchUri: Uri
+ get() {
+ val httpUri = Uri.parse(url)
+ return Uri.parse("vnd.youtube:" + httpUri.getQueryParameter("v"))
+ }
+}
+
+/**
+ * Click listener for Videos. By giving the block a name it helps a reader understand what it does.
+ *
+ */
+class VideoClick(val block: (DevByteVideo) -> Unit) {
+ /**
+ * Called when a video is clicked
+ *
+ * @param video the video that was clicked
+ */
+ fun onClick(video: DevByteVideo) = block(video)
+}
+
+/**
+ * RecyclerView Adapter for setting up data binding on the items in the list.
+ */
+class DevByteAdapter(val callback: VideoClick) : RecyclerView.Adapter() {
+
+ /**
+ * The videos that our Adapter will show
+ */
+ var videos: List = emptyList()
+ set(value) {
+ field = value
+ // For an extra challenge, update this to use the paging library.
+
+ // Notify any registered observers that the data set has changed. This will cause every
+ // element in our RecyclerView to be invalidated.
+ notifyDataSetChanged()
+ }
+
+ /**
+ * Called when RecyclerView needs a new {@link ViewHolder} of the given type to represent
+ * an item.
+ */
+ override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DevByteViewHolder {
+ val withDataBinding: DevbyteItemBinding = DataBindingUtil.inflate(
+ LayoutInflater.from(parent.context),
+ DevByteViewHolder.LAYOUT,
+ parent,
+ false)
+ return DevByteViewHolder(withDataBinding)
+ }
+
+ override fun getItemCount() = videos.size
+
+ /**
+ * Called by RecyclerView to display the data at the specified position. This method should
+ * update the contents of the {@link ViewHolder#itemView} to reflect the item at the given
+ * position.
+ */
+ override fun onBindViewHolder(holder: DevByteViewHolder, position: Int) {
+ holder.viewDataBinding.also {
+ it.video = videos[position]
+ it.videoCallback = callback
+ }
+ }
+
+}
+
+/**
+ * ViewHolder for DevByte items. All work is done by data binding.
+ */
+class DevByteViewHolder(val viewDataBinding: DevbyteItemBinding) :
+ RecyclerView.ViewHolder(viewDataBinding.root) {
+ companion object {
+ @LayoutRes
+ val LAYOUT = R.layout.devbyte_item
+ }
+}
\ No newline at end of file
diff --git a/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt
new file mode 100755
index 0000000..e03a6d4
--- /dev/null
+++ b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.util
+
+import android.view.View
+import android.widget.ImageView
+import androidx.databinding.BindingAdapter
+import com.bumptech.glide.Glide
+
+/**
+ * Binding adapter used to hide the spinner once data is available.
+ */
+@BindingAdapter("isNetworkError", "playlist")
+fun hideIfNetworkError(view: View, isNetWorkError: Boolean, playlist: Any?) {
+ view.visibility = if (playlist != null) View.GONE else View.VISIBLE
+
+ if(isNetWorkError) {
+ view.visibility = View.GONE
+ }
+}
+
+/**
+ * Binding adapter used to display images from URL using Glide
+ */
+@BindingAdapter("imageUrl")
+fun setImageUrl(imageView: ImageView, url: String) {
+ Glide.with(imageView.context).load(url).into(imageView)
+}
\ No newline at end of file
diff --git a/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt
new file mode 100755
index 0000000..8da9996
--- /dev/null
+++ b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.util
+
+private val PUNCTUATION = listOf(", ", "; ", ": ", " ")
+
+/**
+ * Truncate long text with a preference for word boundaries and without trailing punctuation.
+ */
+fun String.smartTruncate(length: Int): String {
+ val words = split(" ")
+ var added = 0
+ var hasMore = false
+ val builder = StringBuilder()
+ for (word in words) {
+ if (builder.length > length) {
+ hasMore = true
+ break
+ }
+ builder.append(word)
+ builder.append(" ")
+ added += 1
+ }
+
+ PUNCTUATION.map {
+ if (builder.endsWith(it)) {
+ builder.replace(builder.length - it.length, builder.length, "")
+ }
+ }
+
+ if (hasMore) {
+ builder.append("...")
+ }
+ return builder.toString()
+}
\ No newline at end of file
diff --git a/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt
new file mode 100755
index 0000000..77d91ad
--- /dev/null
+++ b/DevBytesRepository/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.viewmodels
+
+import android.app.Application
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import com.example.android.devbyteviewer.database.getDatabase
+import com.example.android.devbyteviewer.domain.DevByteVideo
+import com.example.android.devbyteviewer.network.DevByteNetwork
+import com.example.android.devbyteviewer.network.asDomainModel
+import com.example.android.devbyteviewer.repository.VideosRepository
+import kotlinx.coroutines.*
+import java.io.IOException
+
+/**
+ * DevByteViewModel designed to store and manage UI-related data in a lifecycle conscious way. This
+ * allows data to survive configuration changes such as screen rotations. In addition, background
+ * work such as fetching network results can continue through configuration changes and deliver
+ * results after the new Fragment or Activity is available.
+ *
+ * @param application The application that this viewmodel is attached to, it's safe to hold a
+ * reference to applications across rotation since Application is never recreated during actiivty
+ * or fragment lifecycle events.
+ */
+class DevByteViewModel(application: Application) : AndroidViewModel(application) {
+
+
+ /**
+ * The data source this ViewModel will fetch results from.
+ */
+ private val videosRepository = VideosRepository(getDatabase(application))
+
+ /**
+ * A playlist of videos displayed on the screen.
+ */
+ val playlist = videosRepository.videos
+
+ /**
+ * This is the job for all coroutines started by this ViewModel.
+ *
+ * Cancelling this job will cancel all coroutines started by this ViewModel.
+ */
+ private val viewModelJob = SupervisorJob()
+
+ /**
+ * This is the main scope for all coroutines launched by MainViewModel.
+ *
+ * Since we pass viewModelJob, you can cancel all coroutines launched by uiScope by calling
+ * viewModelJob.cancel()
+ */
+ private val viewModelScope = CoroutineScope(viewModelJob + Dispatchers.Main)
+
+ /**
+ * Event triggered for network error. This is private to avoid exposing a
+ * way to set this value to observers.
+ */
+ private var _eventNetworkError = MutableLiveData(false)
+
+ /**
+ * Event triggered for network error. Views should use this to get access
+ * to the data.
+ */
+ val eventNetworkError: LiveData
+ get() = _eventNetworkError
+
+ /**
+ * Flag to display the error message. This is private to avoid exposing a
+ * way to set this value to observers.
+ */
+ private var _isNetworkErrorShown = MutableLiveData(false)
+
+ /**
+ * Flag to display the error message. Views should use this to get access
+ * to the data.
+ */
+ val isNetworkErrorShown: LiveData
+ get() = _isNetworkErrorShown
+
+ /**
+ * init{} is called immediately when this ViewModel is created.
+ */
+ init {
+ refreshDataFromRepository()
+ }
+
+ /**
+ * Refresh data from the repository. Use a coroutine launch to run in a
+ * background thread.
+ */
+ private fun refreshDataFromRepository() {
+ viewModelScope.launch {
+ try {
+ videosRepository.refreshVideos()
+ _eventNetworkError.value = false
+ _isNetworkErrorShown.value = false
+
+ } catch (networkError: IOException) {
+ // Show a Toast error message and hide the progress bar.
+ if(playlist.value!!.isEmpty())
+ _eventNetworkError.value = true
+ }
+ }
+ }
+
+
+ /**
+ * Resets the network error flag.
+ */
+ fun onNetworkErrorShown() {
+ _isNetworkErrorShown.value = true
+ }
+
+
+ /**
+ * Cancel all coroutines when the ViewModel is cleared
+ */
+ override fun onCleared() {
+ super.onCleared()
+ viewModelJob.cancel()
+ }
+
+ /**
+ * Factory for constructing DevByteViewModel with parameter
+ */
+ class Factory(val app: Application) : ViewModelProvider.Factory {
+ override fun create(modelClass: Class): T {
+ if (modelClass.isAssignableFrom(DevByteViewModel::class.java)) {
+ @Suppress("UNCHECKED_CAST")
+ return DevByteViewModel(app) as T
+ }
+ throw IllegalArgumentException("Unable to construct viewmodel")
+ }
+ }
+}
diff --git a/DevBytesRepository/app/src/main/res/drawable-v24/ic_launcher_foreground.xml b/DevBytesRepository/app/src/main/res/drawable-v24/ic_launcher_foreground.xml
new file mode 100755
index 0000000..56a2561
--- /dev/null
+++ b/DevBytesRepository/app/src/main/res/drawable-v24/ic_launcher_foreground.xml
@@ -0,0 +1,50 @@
+
+
+
+
+
+
+ If you return a View from here, you will later be called in
+ * {@link #onDestroyView} when the view is being released.
+ *
+ * @param inflater The LayoutInflater object that can be used to inflate
+ * any views in the fragment,
+ * @param container If non-null, this is the parent view that the fragment's
+ * UI should be attached to. The fragment should not add the view itself,
+ * but this can be used to generate the LayoutParams of the view.
+ * @param savedInstanceState If non-null, this fragment is being re-constructed
+ * from a previous saved state as given here.
+ *
+ * @return Return the View for the fragment's UI.
+ */
+ override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
+ savedInstanceState: Bundle?): View? {
+ val binding: FragmentDevByteBinding = DataBindingUtil.inflate(
+ inflater,
+ R.layout.fragment_dev_byte,
+ container,
+ false)
+ // Set the lifecycleOwner so DataBinding can observe LiveData
+ binding.setLifecycleOwner(viewLifecycleOwner)
+
+ binding.viewModel = viewModel
+
+ viewModelAdapter = DevByteAdapter(VideoClick {
+ // When a video is clicked this block or lambda will be called by DevByteAdapter
+
+ // context is not around, we can safely discard this click since the Fragment is no
+ // longer on the screen
+ val packageManager = context?.packageManager ?: return@VideoClick
+
+ // Try to generate a direct intent to the YouTube app
+ var intent = Intent(Intent.ACTION_VIEW, it.launchUri)
+ if(intent.resolveActivity(packageManager) == null) {
+ // YouTube app isn't found, use the web url
+ intent = Intent(Intent.ACTION_VIEW, Uri.parse(it.url))
+ }
+
+ startActivity(intent)
+ })
+
+ binding.root.findViewById(R.id.recycler_view).apply {
+ layoutManager = LinearLayoutManager(context)
+ adapter = viewModelAdapter
+ }
+
+
+ // Observer for the network error.
+ viewModel.eventNetworkError.observe(this, Observer { isNetworkError ->
+ if (isNetworkError) onNetworkError()
+ })
+
+ return binding.root
+ }
+
+ /**
+ * Method for displaying a Toast error message for network errors.
+ */
+ private fun onNetworkError() {
+ if(!viewModel.isNetworkErrorShown.value!!) {
+ Toast.makeText(activity, "Network Error", Toast.LENGTH_LONG).show()
+ viewModel.onNetworkErrorShown()
+ }
+ }
+
+ /**
+ * Helper method to generate YouTube app links
+ */
+ private val DevByteVideo.launchUri: Uri
+ get() {
+ val httpUri = Uri.parse(url)
+ return Uri.parse("vnd.youtube:" + httpUri.getQueryParameter("v"))
+ }
+}
+
+/**
+ * Click listener for Videos. By giving the block a name it helps a reader understand what it does.
+ *
+ */
+class VideoClick(val block: (DevByteVideo) -> Unit) {
+ /**
+ * Called when a video is clicked
+ *
+ * @param video the video that was clicked
+ */
+ fun onClick(video: DevByteVideo) = block(video)
+}
+
+/**
+ * RecyclerView Adapter for setting up data binding on the items in the list.
+ */
+class DevByteAdapter(val callback: VideoClick) : RecyclerView.Adapter() {
+
+ /**
+ * The videos that our Adapter will show
+ */
+ var videos: List = emptyList()
+ set(value) {
+ field = value
+ // For an extra challenge, update this to use the paging library.
+
+ // Notify any registered observers that the data set has changed. This will cause every
+ // element in our RecyclerView to be invalidated.
+ notifyDataSetChanged()
+ }
+
+ /**
+ * Called when RecyclerView needs a new {@link ViewHolder} of the given type to represent
+ * an item.
+ */
+ override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DevByteViewHolder {
+ val withDataBinding: DevbyteItemBinding = DataBindingUtil.inflate(
+ LayoutInflater.from(parent.context),
+ DevByteViewHolder.LAYOUT,
+ parent,
+ false)
+ return DevByteViewHolder(withDataBinding)
+ }
+
+ override fun getItemCount() = videos.size
+
+ /**
+ * Called by RecyclerView to display the data at the specified position. This method should
+ * update the contents of the {@link ViewHolder#itemView} to reflect the item at the given
+ * position.
+ */
+ override fun onBindViewHolder(holder: DevByteViewHolder, position: Int) {
+ holder.viewDataBinding.also {
+ it.video = videos[position]
+ it.videoCallback = callback
+ }
+ }
+
+}
+
+/**
+ * ViewHolder for DevByte items. All work is done by data binding.
+ */
+class DevByteViewHolder(val viewDataBinding: DevbyteItemBinding) :
+ RecyclerView.ViewHolder(viewDataBinding.root) {
+ companion object {
+ @LayoutRes
+ val LAYOUT = R.layout.devbyte_item
+ }
+}
\ No newline at end of file
diff --git a/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt
new file mode 100755
index 0000000..e03a6d4
--- /dev/null
+++ b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/BindingAdapters.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.util
+
+import android.view.View
+import android.widget.ImageView
+import androidx.databinding.BindingAdapter
+import com.bumptech.glide.Glide
+
+/**
+ * Binding adapter used to hide the spinner once data is available.
+ */
+@BindingAdapter("isNetworkError", "playlist")
+fun hideIfNetworkError(view: View, isNetWorkError: Boolean, playlist: Any?) {
+ view.visibility = if (playlist != null) View.GONE else View.VISIBLE
+
+ if(isNetWorkError) {
+ view.visibility = View.GONE
+ }
+}
+
+/**
+ * Binding adapter used to display images from URL using Glide
+ */
+@BindingAdapter("imageUrl")
+fun setImageUrl(imageView: ImageView, url: String) {
+ Glide.with(imageView.context).load(url).into(imageView)
+}
\ No newline at end of file
diff --git a/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt
new file mode 100755
index 0000000..8da9996
--- /dev/null
+++ b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/util/Util.kt
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.util
+
+private val PUNCTUATION = listOf(", ", "; ", ": ", " ")
+
+/**
+ * Truncate long text with a preference for word boundaries and without trailing punctuation.
+ */
+fun String.smartTruncate(length: Int): String {
+ val words = split(" ")
+ var added = 0
+ var hasMore = false
+ val builder = StringBuilder()
+ for (word in words) {
+ if (builder.length > length) {
+ hasMore = true
+ break
+ }
+ builder.append(word)
+ builder.append(" ")
+ added += 1
+ }
+
+ PUNCTUATION.map {
+ if (builder.endsWith(it)) {
+ builder.replace(builder.length - it.length, builder.length, "")
+ }
+ }
+
+ if (hasMore) {
+ builder.append("...")
+ }
+ return builder.toString()
+}
\ No newline at end of file
diff --git a/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt
new file mode 100755
index 0000000..77d91ad
--- /dev/null
+++ b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/viewmodels/DevByteViewModel.kt
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.viewmodels
+
+import android.app.Application
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import com.example.android.devbyteviewer.database.getDatabase
+import com.example.android.devbyteviewer.domain.DevByteVideo
+import com.example.android.devbyteviewer.network.DevByteNetwork
+import com.example.android.devbyteviewer.network.asDomainModel
+import com.example.android.devbyteviewer.repository.VideosRepository
+import kotlinx.coroutines.*
+import java.io.IOException
+
+/**
+ * DevByteViewModel designed to store and manage UI-related data in a lifecycle conscious way. This
+ * allows data to survive configuration changes such as screen rotations. In addition, background
+ * work such as fetching network results can continue through configuration changes and deliver
+ * results after the new Fragment or Activity is available.
+ *
+ * @param application The application that this viewmodel is attached to, it's safe to hold a
+ * reference to applications across rotation since Application is never recreated during actiivty
+ * or fragment lifecycle events.
+ */
+class DevByteViewModel(application: Application) : AndroidViewModel(application) {
+
+
+ /**
+ * The data source this ViewModel will fetch results from.
+ */
+ private val videosRepository = VideosRepository(getDatabase(application))
+
+ /**
+ * A playlist of videos displayed on the screen.
+ */
+ val playlist = videosRepository.videos
+
+ /**
+ * This is the job for all coroutines started by this ViewModel.
+ *
+ * Cancelling this job will cancel all coroutines started by this ViewModel.
+ */
+ private val viewModelJob = SupervisorJob()
+
+ /**
+ * This is the main scope for all coroutines launched by MainViewModel.
+ *
+ * Since we pass viewModelJob, you can cancel all coroutines launched by uiScope by calling
+ * viewModelJob.cancel()
+ */
+ private val viewModelScope = CoroutineScope(viewModelJob + Dispatchers.Main)
+
+ /**
+ * Event triggered for network error. This is private to avoid exposing a
+ * way to set this value to observers.
+ */
+ private var _eventNetworkError = MutableLiveData(false)
+
+ /**
+ * Event triggered for network error. Views should use this to get access
+ * to the data.
+ */
+ val eventNetworkError: LiveData
+ get() = _eventNetworkError
+
+ /**
+ * Flag to display the error message. This is private to avoid exposing a
+ * way to set this value to observers.
+ */
+ private var _isNetworkErrorShown = MutableLiveData(false)
+
+ /**
+ * Flag to display the error message. Views should use this to get access
+ * to the data.
+ */
+ val isNetworkErrorShown: LiveData
+ get() = _isNetworkErrorShown
+
+ /**
+ * init{} is called immediately when this ViewModel is created.
+ */
+ init {
+ refreshDataFromRepository()
+ }
+
+ /**
+ * Refresh data from the repository. Use a coroutine launch to run in a
+ * background thread.
+ */
+ private fun refreshDataFromRepository() {
+ viewModelScope.launch {
+ try {
+ videosRepository.refreshVideos()
+ _eventNetworkError.value = false
+ _isNetworkErrorShown.value = false
+
+ } catch (networkError: IOException) {
+ // Show a Toast error message and hide the progress bar.
+ if(playlist.value!!.isEmpty())
+ _eventNetworkError.value = true
+ }
+ }
+ }
+
+
+ /**
+ * Resets the network error flag.
+ */
+ fun onNetworkErrorShown() {
+ _isNetworkErrorShown.value = true
+ }
+
+
+ /**
+ * Cancel all coroutines when the ViewModel is cleared
+ */
+ override fun onCleared() {
+ super.onCleared()
+ viewModelJob.cancel()
+ }
+
+ /**
+ * Factory for constructing DevByteViewModel with parameter
+ */
+ class Factory(val app: Application) : ViewModelProvider.Factory {
+ override fun create(modelClass: Class): T {
+ if (modelClass.isAssignableFrom(DevByteViewModel::class.java)) {
+ @Suppress("UNCHECKED_CAST")
+ return DevByteViewModel(app) as T
+ }
+ throw IllegalArgumentException("Unable to construct viewmodel")
+ }
+ }
+}
diff --git a/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/work/RefreshDataWorker.kt b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/work/RefreshDataWorker.kt
new file mode 100644
index 0000000..14d5693
--- /dev/null
+++ b/DevBytesWorkManager/app/src/main/java/com/example/android/devbyteviewer/work/RefreshDataWorker.kt
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.devbyteviewer.work
+
+import android.content.Context
+import androidx.work.CoroutineWorker
+import androidx.work.WorkerParameters
+import com.example.android.devbyteviewer.database.getDatabase
+import com.example.android.devbyteviewer.repository.VideosRepository
+import retrofit2.HttpException
+import timber.log.Timber
+
+class RefreshDataWorker(appContext: Context, params: WorkerParameters) :
+ CoroutineWorker(appContext, params) {
+
+ companion object {
+ const val WORK_NAME = "com.example.android.devbyteviewer.work.RefreshDataWorker"
+ }
+ override suspend fun doWork(): Result {
+ val database = getDatabase(applicationContext)
+ val repository = VideosRepository(database)
+
+ try {
+ repository.refreshVideos( )
+ Timber.d("WorkManager: Work request for sync is run")
+ } catch (e: HttpException) {
+ return Result.retry()
+ }
+
+ return Result.success()
+ }
+}
\ No newline at end of file
diff --git a/DevBytesWorkManager/app/src/main/res/drawable-v24/ic_launcher_foreground.xml b/DevBytesWorkManager/app/src/main/res/drawable-v24/ic_launcher_foreground.xml
new file mode 100755
index 0000000..56a2561
--- /dev/null
+++ b/DevBytesWorkManager/app/src/main/res/drawable-v24/ic_launcher_foreground.xml
@@ -0,0 +1,50 @@
+
+
+
+
+
+
+