read28.md

RecyclerView

RecyclerView for displaying lists of data

• With RecyclerView -> it's easy to efficiently display large sets of data.

Note: Besides being the name of the class, RecyclerView is also the name of the library.

Key classes

• RecyclerView is the ViewGroup that contains the views corresponding to your data.

• Each individual element in the list is defined by a view holder object. After the view holder is created, the RecyclerView binds it to its data. You define the view holder by extending RecyclerView.ViewHolder.

• The RecyclerView requests those views, by calling methods in the adapter. You define the adapter by extending RecyclerView.Adapter.

• The layout manager arranges the individual elements in your list.

Plan your layout

• RecyclerView items are arranged by a LayoutManager class.
• The RecyclerView library provides three layout managers:

1. LinearLayoutManager -> arranges the items in a one-dimensional list.
2. GridLayoutManager arranges all items in a two-dimensional grid: vertically or horizontally.
3. StaggeredGridLayoutManager is similar to GridLayoutManager, but it does not require that items in a row have the same height (for vertical grids) or items in the same column have the same width (for horizontal grids).

Implementing your adapter and view holder

After implementing layout, you need to implement your Adapter and ViewHolder. The ViewHolder is a wrapper around a View that contains the layout for an individual item in the list. The Adapter creates ViewHolder objects as needed, and also sets the data for those views. binding is :The process of associating views to their data.

When you define your adapter, you need to override three key methods:

1. onCreateViewHolder(): RecyclerView calls this method whenever it needs to create a new ViewHolder. It creates and initializes, but does not fill in the view's contents.

2. onBindViewHolder(): The method fetches the appropriate data and uses the data to fill in the view holder's layout.

3. getItemCount(): RecyclerView calls this method to get the size of the data set.

The Example that from the link:

1. Java Class

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {

    private String[] localDataSet;

    /**
     * Provide a reference to the type of views that you are using
     * (custom ViewHolder).
     */
    public static class ViewHolder extends RecyclerView.ViewHolder {
        private final TextView textView;

        public ViewHolder(View view) {
            super(view);
            // Define click listener for the ViewHolder's View

            textView = (TextView) view.findViewById(R.id.textView);
        }

        public TextView getTextView() {
            return textView;
        }
    }

    /**
     * Initialize the dataset of the Adapter.
     *
     * @param dataSet String[] containing the data to populate views to be used
     * by RecyclerView.
     */
    public CustomAdapter(String[] dataSet) {
        localDataSet = dataSet;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
        // Create a new view, which defines the UI of the list item
        View view = LayoutInflater.from(viewGroup.getContext())
                .inflate(R.layout.text_row_item, viewGroup, false);

        return new ViewHolder(view);
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder viewHolder, final int position) {

        // Get element from your dataset at this position and replace the
        // contents of the view with that element
        viewHolder.getTextView().setText(localDataSet[position]);
    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return localDataSet.length;
    }
}

2. text_row_item.xml file like this:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/list_item_height"
    android:layout_marginLeft="@dimen/margin_medium"
    android:layout_marginRight="@dimen/margin_medium"
    android:gravity="center_vertical">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/element_text"/>
</FrameLayout>