tutorials for android app development for beginners java Adapter Class Urdu #3

Adapters
An adapter manages the data model and adapts it to the individual entries in the widget. It extends the RecyclerView.Adapter class and is assigned to the recycler view via the #RecyclerView.setAdapter method. The input to the adapter of an recycler view can be any arbitrary Java objects. Based on this input the adapter must return the total number of items via its getItemCount() method.

The #adapter prepares the layout of the items by inflating the correct layout for the individual data elements. This work is done in the onCreateViewHolder method. It returns an object of type #ViewHolder per visual entry in the recycler view.

This instance is used to access the views in the inflated layout. The #onCreateViewHolder method is only called then a new view must be created.

Every visible entry in a recycler view is filled with the correct data model item by the adapter. Once a data item becomes visible, the adapter assigns this data to the individual widgets which he inflated earlier. This work in done in the onBindViewHolder method.

For example, an entry in a list may have an image on the left side and two text lines in the middle as depicted in the following graphic.
Creating the RecyclerView.Adapter
Here we need to create the adapter which will actually populate the data into the RecyclerView. The adapter's role is to convert an object at a position into a list row item to be inserted.

However, with a RecyclerView the adapter requires the existence of a "ViewHolder" object which describes and provides access to all the views within each item row. We can create the basic empty adapter and holder together
Every adapter has three primary methods: onCreateViewHolder to inflate the item layout and create the holder, onBindViewHolder to set the view attributes based on the data and getItemCount to determine the number of items. We need to implement all three to finish the adapter: