When I run the app, the fragments content is blank.
Even though the log statements show, the list is populated. I tried implementing a favorite post feature. You can add/remove a favorite post to your list. This works fine.
The goal:
I want to display the favorite posts in FavoritePostsOverViewFragment. Using a recyclerView.
I'm also trying to follow MVVM architecture. Using a Room database. (no API at this point)
The problem(s):
- Working with the 2 different objects seems a bit weird the way I do it right now. But it is populated at the moment
Please refer to the part "How I am getting the posts based on if they have been favorite by a user"
Is there a less complex way of writing this? - The Binding Adapter is null / empty, not displaying the posts.
I am using the Adapter already in another fragment, it works fine there. I can see a list of posts and use the click listeners. So In my thoughts, I eliminated the adapter as a problem for this case.
The two data classes used:
data class Post(
var Id: Long = 0L,
var Text: String = "",
var Picture: Bitmap? = null,
var Link: String = "",
var UserId: String = "",
var UserEmail: String = ""
)
data class Favorite(
var Id: Long = 0L,
var UserId: String = "",
var PostId: Long = 0L
)
The Adapter
lass PostAdapter(val clickListener: PostListener, val favoriteListener: FavoriteListener) :
ListAdapter<Post, ViewHolder>(PostDiffCallback()) {
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val item = getItem(position)
holder.bind(clickListener, favoriteListener, item)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder.from(parent)
}
}
class ViewHolder(val binding: PostListItemBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(clickListener: PostListener, favoriteListener: FavoriteListener, item: Post) {
binding.post = item
binding.clickListener = clickListener
binding.favoriteListener = favoriteListener
binding.executePendingBindings()
}
companion object {
fun from(parent: ViewGroup): ViewHolder {
val layoutInflater = LayoutInflater.from(parent.context)
println(layoutInflater.toString())
val binding = PostListItemBinding.inflate(layoutInflater, parent, false)
return ViewHolder(binding)
}
}
}
class PostDiffCallback : DiffUtil.ItemCallback<Post>() {
override fun areItemsTheSame(oldItem: Post, newItem: Post): Boolean {
return oldItem.Id == newItem.Id
}
override fun areContentsTheSame(oldItem: Post, newItem: Post): Boolean {
return oldItem == newItem
}
}
class PostListener(val clickListener: (post: Post) -> Unit) {
fun onClick(post: Post) = clickListener(post)
}
class FavoriteListener(val clickListener: (post: Post) -> Unit) {
fun onClick(post: Post) = clickListener(post)
}
How I am getting the posts based on if they have been favorite by a user.
class PostRepository(private val faithDatabase: FaithDatabase) {
suspend fun getUserFavs(): List<Long> {
return withContext(Dispatchers.IO) {
faithDatabase.favoriteDatabaseDao.getUserFavorites(CredentialsManager.cachedUserProfile?.getId()!!)
}
}
suspend fun getFavos(): LiveData<List<Post>> {
val _items: MutableLiveData<List<Post>> = MutableLiveData(listOf())
val items: LiveData<List<Post>> = _items
val postIds: List<Long>
var dbPost: DatabasePost
withContext(Dispatchers.IO) {
postIds = getUserFavs()
}
for (id in postIds) {
withContext(Dispatchers.IO) {
dbPost = faithDatabase.postDatabaseDao.get(id)
}
val post = Post(
Text = dbPost.Text,
UserId = dbPost.UserId,
UserEmail = dbPost.UserEmail,
Link = dbPost.Link,
Picture = dbPost.Picture,
Id = dbPost.Id
)
_items.value = _items.value?.plus(post) ?: listOf(post)
}
Timber.i("items= " + items.value!!.size)
/*this logs=
I/PostRepository: items= 2*/
return items
}
My FavoritePostOverViewModel
class FavoritePostsOverviewViewModel(val database: PostDatabaseDao, app: Application) :
AndroidViewModel(app) {
private val db = FaithDatabase.getInstance(app.applicationContext)
private val postRepository = PostRepository(db)
var posts: LiveData<List<Post>>? = null
init {
viewModelScope.launch {
posts = repository.getFavos()
Timber.i(posts!!.value.toString())
/* this logs=
I/FavoritePostsOverviewViewModel: [Post(Id=1, Text=Name, Picture=android.graphics.Bitmap@ef3b553, Link=Add your link here, UserId=auth0|62cc0d4441814675a5906130, UserEmail=jdecorte6@gmail.com), Post(Id=4, Text=test, Picture=android.graphics.Bitmap@35ae90, Link=www.google.com, UserId=auth0|62cc0d4441814675a5906130, UserEmail=jdecorte6@gmail.com)]*/
}
}
my FavoritePostsOverViewFragment
class FavoritePostsOverViewFragment : Fragment() {
lateinit var binding: FragmentFavoritePostsBinding
private lateinit var favoritePostsOverviewViewModel: FavoritePostsOverviewViewModel
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// setup the db connection
val application = requireNotNull(this.activity).application
val dataSource = FaithDatabase.getInstance(application).postDatabaseDao
// create the factory + viewmodel
val viewModelFactory = FavoritePostsOverviewViewModelFactory(dataSource, application)
favoritePostsOverviewViewModel =
ViewModelProvider(this, viewModelFactory)[FavoritePostsOverviewViewModel::class.java]
binding =
DataBindingUtil.inflate(inflater, R.layout.fragment_favorite_posts, container, false)
// Giving the binding access to the favoritePostsOverviewViewModel
binding.favoritePostsOverviewViewModel = favoritePostsOverviewViewModel
// Allows Data Binding to Observe LiveData with the lifecycle of this Fragment
binding.lifecycleOwner = this
// Sets the adapter of the PostAdapter RecyclerView with clickHandler lambda that
// tells the viewModel when our property is clicked
binding.postList.adapter = PostAdapter(PostListener {
favoritePostsOverviewViewModel.displayPropertyDetails(it)
}, FavoriteListener {
favoritePostsOverviewViewModel.FavoriteClick(it)
})
return binding.root
}
I have a Binding Adapter
@BindingAdapter("listData")
fun bindRecyclerViewPost(recyclerView: RecyclerView, data: List<Post>?) {
if (data.isNullOrEmpty()) {
return
}
val adapter = recyclerView.adapter as PostAdapter
adapter.submitList(data)
}
Used in the XML
<?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"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="favoritePostsOverviewViewModel"
type="com.example.ep3_devops_faith.ui.post.favorites.FavoritePostsOverviewViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/post_list"
android:layout_width="0dp"
android:layout_height="0dp"
android:clipToPadding="false"
android:padding="6dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:listData="@{favoritePostsOverviewViewModel.posts}"
tools:listitem="@layout/post_list_item"
tools:itemCount="16"/>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
referenced articles:
Android BindingAdapter order of execution?
LiveData Observer in BindingAdapter
https://developer.android.com/topic/architecture
https://developer.android.com/topic/libraries/data-binding/binding-adapters
https://play.kotlinlang.org/hands-on/Introduction%20to%20Coroutines%20and%20Channels/01_Introduction
