RecyclerView

• RecyclerView is a view group that's used to efficiently display large sets of data by recycling views as they scroll off the screen.

• It's an advanced version of ListView and GridView, offering better performance and more customizable features.

Adapter:

• The RecyclerView requires an adapter that manages the data and creates views for individual items. This adapter extends RecyclerView.Adapter and overrides methods like
1. onCreateViewHolder (to create new views),
2. onBindViewHolder (to bind data to views),
3. and getItemCount (to determine the number of items).

LayoutManager:

• RecyclerView uses a LayoutManager to position items within the view. There are different layout managers available such as
1. LinearLayoutManager,

// inside fragment use context
binding.homeRecycleView.layoutManager = LinearLayoutManager(context)

// inside activity use this@ActivityName 
// context , orientation , isReversed 
binding.homeRecycleView.layoutManager = 
					LinearLayoutManager(this@YourActivity,LinearLayoutManager.HORIZONTAL,false)

2. GridLayoutManager

// contex and spanCount( Column Count )
binding.homeRecycleView.layoutManager = GridLayoutManager(context,2)

// context , spanCount , Orientation , isReversedList
binding.homeRecycleView.layoutManager = 
							GridLayoutManager(this@YourActivity,2,GridLayoutManager.VERTICAL,false)

3. StaggeredGridLayoutManager.

binding.homeRecycleView.layoutManager = 
						StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)

They control how items are arranged, scrolled, and recycled.
 

ViewHolder:

• The ViewHolder pattern is used to cache views of individual items. It helps in recycling the views that are no longer visible on the screen, making scrolling smoother and more efficient.

Item Decoration:

• ItemDecoration allows customization of individual item views by adding decorations such as spacing, dividers, or decorators between items.
1. ItemAnimator: It provides animations for adding, removing, and updating items within the RecyclerView.
2. Click Listeners: To handle user interactions like item clicks or long presses, you can set click listeners within the adapter.
3. Data Set Changes: The adapter can notify the RecyclerView of any changes in the underlying dataset. Methods like notifyItemInserted, notifyItemRemoved, etc., help in reflecting changes in the UI.
 
 

• Defining a layout for individual items in a separate XML file.

• Creating an adapter by extending RecyclerView.Adapter and implementing required methods.

• Setting up the RecyclerView in your activity or fragment, specifying the adapter, layout manager, and any other configurations.

• Populating the RecyclerView with data by setting the adapter and handling interactions.

• The RecyclerView is highly customizable and efficient for handling large data sets, making it a preferred choice for displaying lists or grids in Android applications. Its ability to recycle views efficiently helps in achieving smooth scrolling and improved performance, especially when dealing with extensive data.

Programmatically Set Attributes in Kotlin:

1. recyclerView.layoutManager:
• Sets the layout manager programmatically. For example:
1. LinearLayoutManager,

// inside fragment use context
binding.homeRecycleView.layoutManager = LinearLayoutManager(context)

// inside activity use this@ActivityName 
// context , orientation , isReversed 
binding.homeRecycleView.layoutManager = 
					LinearLayoutManager(this@YourActivity,LinearLayoutManager.HORIZONTAL,false)

2. GridLayoutManager

// contex and spanCount( Column Count )
binding.homeRecycleView.layoutManager = GridLayoutManager(context,2)

// context , spanCount , Orientation , isReversedList
binding.homeRecycleView.layoutManager = 
							GridLayoutManager(this@YourActivity,2,GridLayoutManager.VERTICAL,false)

3. StaggeredGridLayoutManager.

binding.homeRecycleView.layoutManager = 
						StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)

2. recyclerView.adapter:
• Sets the adapter for the RecyclerView. For example:

val adapter = CustomAdapter(this@MainActivity , items)
recyclerView.adapter = adapter

3. Other properties:
• You can also modify other properties programmatically, such as padding, item decorations, animations, and click listeners:

recyclerView.addItemDecoration(DividerItemDecoration(this, LinearLayoutManager.VERTICAL))
recyclerView.itemAnimator = DefaultItemAnimator()

Adapter and ViewHolder:

When creating a custom adapter, attributes and methods within the adapter and its ViewHolder here it is Myclass that is inherited by RecyclerView.ViewHolder() to work as viewHolder for the adapter , here are some significant:
1. onCreateViewHolder:
• Inflates the layout for individual items and initializes the ViewHolder.
2. onBindViewHolder:
• Binds data to the views within the ViewHolder.
3. getItemCount:
• Specifies the total number of items in the RecyclerView.
4. Myclass:
• Contains references to views within the item layout, allowing for efficient recycling and manipulation.

Customization:

Customize the RecyclerView behavior and appearance through various methods and attributes based on your requirements, such as animations, decorations, click listeners, and more.
These attributes and methods offer control over how the RecyclerView displays and manages the list of items in your Android application. Each attribute provides a way to customize the behavior and appearance of the RecyclerView and its associated components.

Kotlin Code (MainActivity.kt):

This Kotlin code sets up the RecyclerView with an adapter to display a list of items.

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val recyclerView: RecyclerView = findViewById(R.id.recyclerView)
        recyclerView.layoutManager = LinearLayoutManager(this)

        val items = listOf("Item 1", "Item 2", "Item 3", "Item 4", "Item 5")

        val adapter = CustomAdapter(items)
        recyclerView.adapter = adapter
    }
}

 

MyRecAdapter.kt

// extends to RecyclerView adapter with our class that resides in our main Adapter class
class MyRecAdapter(var mainActivity: MainActivity, var userList: ArrayList<User>) :    RecyclerView.Adapter<MyRecAdapter.Myclass>() {

    // Class holds the  View that has to be craated
    class Myclass(itemView: View) : RecyclerView.ViewHolder(itemView) {

        var name : TextView
        var username : TextView
        var email : TextView
				var submit : Button 
        // our view's objects connect in init block with id in view layout
        init {
            name  = itemView.findViewById(R.id.name)
            username  = itemView.findViewById(R.id.username)
            email  = itemView.findViewById(R.id.email)
            submit  = itemView.findViewById(R.id.submit)
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): Myclass {
        var view = LayoutInflater.from(mainActivity).inflate(R.layout.myitem, parent, false)
        return Myclass(view)
    }

    override fun getItemCount(): Int = userList.size

    override fun onBindViewHolder(holder: Myclass, position: Int) {
        holder.name.text = userList[position].name
        holder.username.text = userList[position].username
        holder.email.text = userList[position].email
				
				// to perform some action on click of button resides in item 
				holder.submit.setOnClickListener 
						// action to be perfomed on click 			
				}

				// if you want to click on whole item view than 
				holder.itemView.setOnClickListener {
							// action to be performed on click on whole item 
				}
    }
}

 
Explanation:
• recyclerview_item.xml defines the layout for individual items in the list.
• In MainActivity.kt, the RecyclerView and its layout manager are initialized.
• A list of items is created (items), and a custom adapter (CustomAdapter) is created and attached to the RecyclerView.
• The adapter inflates the recyclerview_item.xml layout for each item and binds data to the TextView inside it.
 
• Put some statement to performed on click of button on item holder.submit.setOnClickListener {...}
• here submit is instance of button that connected with id of that view
 
• Performed some action on click of whole one item of list
holder.itemView.setOnClickListener {...}
• here itemView refers to the item that has been clicked and action to be performed based on that
 

Drag And Drop in RecyclerView