RecyclerView with Data Binding

Question 1

What is the class signature for an Adapter that uses a ViewHolder which is defined within the Adapter class itself?

Answer 1

class MyAdapter : RecyclerView.Adapter^MyAdapter.MyViewHolder^()

Question 2

What is Context?

Answer 2

An interface to global information about an application environment.
An abstract class whose implementation is provided by the Android system.

Question 3

What can a Context provide access to?

Answer 3

App-specific resources and classes
Up-calls for app-level operations, ie
-launching Activities
-broadcasting and receiving Intents

Question 4

In which class should a ViewHolder’s Views be set?

Answer 4

Set the Views in a ViewHolder.bind() function, then call holder.bind from Adapter.onBindViewHolder()

Question 5

In which class should the ViewHolder’s View be inflated?

Answer 5

In a companion object of the ViewHolder class, so the function responsible for inflating can be called from Adapter.onCreateViewHolder()

Question 6

Why is the ViewHolder’s constructor private?

Answer 6

Because the companion object returns a ViewHolder instance, the constructor never needs to be called

Question 7

What is the class signature when extending DiffUtil.ItemCallback?

Answer 7

class MyListObjectDiffCallback: DiffUtil.ItemCallback^MyListObject^()

Question 8

What functions are implemented when extending DiffUtil.ItemCallback?

Answer 8

areItemsTheSame(oldItem: MyListObject, newItem: MyListObject): Boolean

areContentsTheSame(oldItem: MyListObject, newItem: MyListObject): Boolean

Question 9

What is the role of a ListAdapter?

Answer 9

Keeps track of the list and notifies the Adapter when the list is updated

Question 10

What is the class signature for implementing a ListAdapter?

Answer 10

class MyAdapter: ListAdapter^MyListObject, MyViewHolder^(MyListObjectDiffCallback( ) )

Question 11

What can be removed from the Adapter when the ListAdapter is implemented?

Answer 11

The property keeping track of the list of data

The function getItemCount( )

Question 12

Where does the function getItem(position) (provided by ListAdapter) need to be used?

Answer 12

Adapter.onBindViewHolder()
getItem(position) returns the item to be displayed - the function is provided as the list is not available to the Adapter when the responsibility of maintaining the list is taken over by the ListAdapter

Question 13

How do you use ListAdapter.submitList() ?

Answer 13

In Fragment.onCreateView()
Call submitList(list) on the adapter property that has been attached to the recyclerView.
This will likely be in the lambda of the observer of the LiveData^List^

Question 14

What is the difference between inflating a ViewHolder View with and without data binding?

Answer 14

Without data binding:

• inflate a view using layoutInflater.inflate()
• pass the view to the returned MyViewHolder(view)
• this is passed to the parent RecyclerView.ViewHolder(view)

With data binding:

• inflate a binding object using GeneratedViewDataBinding.inflate(layoutInflater, parent, false)
• pass the binding in as the parameter to instantiate the returned MyViewHolder(binding)
• The parent RecyclerView.ViewHolder requires a view as its parameter, so pass in binding.root

Question 15

How does the ViewHolder class signature change when implementing data binding?

Answer 15

• (itemView: View) becomes (binding: GeneratedViewDataBinding) (name will match the layout xml to be inflated)
• Put “val” in front of “binding” in the constructor so binding is initialised when the constructor is called and can be used throughout the ViewHolder class.
• binding.root replaces itemView being passed to parent RecyclerView.ViewHolder

Question 16

What is the syntax for setting inlined views using the binding object in onBindViewHolder()?

Answer 16

binding.view.text = “String”

Question 17

What are the steps to implement binding adapters in the bind() function?

Answer 17

• Create BindingUtils.kt file
• Create @BindingAdapters - extension functions that set the views in the ViewHolder
• Replace (inline) binding setters with
  a) binding.layoutXmlDataVariableName = item
  b) binding.executePendingBindings( )
• Add bindings to the xml layout using
  
  • app:functionIdentifier=”@{layoutXmlDataVariableName}

Question 18

In the bind() function, what is the purpose of

binding.layoutXmlDataVariableName = item

Answer 18

It associates the ViewHolder’s entity instance with the binding

Question 19

In the bind function, what is the purpose of

binding.executePendingBindings( )

Answer 19

It executes any pending @BindingAdapter functions right away, immediately setting the Views in the ViewHolder

Question 20

What arguments does a GridLayoutManager take?

Answer 20

1. context (pass “activity”)
2. noOfColumns: Int
3. GridLayoutManager.VERTICAL //vertical is the default orientation
4. isReverseLayout: Boolean

(3 and 4 optional)

Question 21

How do you set the RecyclerView’s LayoutManager to GridLayoutManager?

Answer 21

In Fragment.onCreateView()
val manager = GridLayoutManager(…)
binding.recyclerViewsLayoutXmlId.layoutManager = manager

Question 22

How do Binding Adapter functions need to change once click listeners and handlers are implemented on the RecyclerView?

Answer 22

Items being passed to @BindingAdapter methods might now be nullable. Make the item argument to be of nullable type and wrap functionality in item?.let{ }