In this document
The support library in the Android L Developer Preview contains two new widgets,
RecyclerView
and CardView
. Use these widgets to show complex lists
and cards in your app. These widgets have material design style by default.
RecyclerView
RecyclerView
is a more advanced and flexible version of ListView
.
This widget is a container for large sets of views that can be recycled and scrolled very
efficiently. Use the RecyclerView
widget when you have lists with elements that
change dynamically.
RecyclerView
is easy to use, because it provides:
- A layout manager for positioning items
- Default animations for common item operations
You also have the flexibility to define custom layout managers and animations for this widget.
To use the RecyclerView
widget, you have to specify an adapter and a layout
manager. To create an adapter, you extend the RecyclerView.Adapter
class. The details
of the implementation depend on the specifics of your dataset and the type of views. For more
information, see the examples below.
A layout manager positions item views inside a RecyclerView
and
determines when to reuse item views that are no longer visible to the user. To reuse (or
recycle) a view, a layout manager may ask the adapter to replace the content of the
view with a different element from the dataset. Recycling views in this manner improves
performance by avoiding the creation of unnecessary views or performing expensive
findViewById
lookups.
RecyclerView
provides LinearLayoutManager
, which shows the items in a
vertical or horizontal scrolling list. To create a custom layout, you extend the
RecyclerView.LayoutManager
class.
Animations
Animations for adding and removing items are enabled by default in RecyclerView
.
To customize these animations, extend the RecyclerView.ItemAnimator
class and use
the RecyclerView.setItemAnimator
method.
Examples
To include a RecyclerView
in your layout:
<!-- A RecyclerView with some commonly used attributes --> <android.support.v7.widget.RecyclerView android:id="@+id/my_recycler_view" android:scrollbars="vertical" android:layout_width="match_parent" android:layout_height="match_parent"/>
To get the RecyclerView
object in your activity:
public class MyActivity extends Activity { private RecyclerView mRecyclerView; private RecyclerView.Adapter mAdapter; private RecyclerView.LayoutManager mLayoutManager; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.my_activity); mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view); // improve performance if you know that changes in content // do not change the size of the RecyclerView mRecyclerView.setHasFixedSize(true); // use a linear layout manager mLayoutManager = new LinearLayoutManager(this); mRecyclerView.setLayoutManager(mLayoutManager); // specify an adapter (see also next example) mAdapter = new MyAdapter(myDataset); mRecyclerView.setAdapter(mAdapter); } ... }
To create a simple adapter:
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> { private String[] mDataset; // Provide a reference to the type of views that you are using // (custom viewholder) public static class ViewHolder extends RecyclerView.ViewHolder { public TextView mTextView; public ViewHolder(TextView v) { super(v); mTextView = v; } } // Provide a suitable constructor (depends on the kind of dataset) public MyAdapter(String[] myDataset) { mDataset = myDataset; } // Create new views (invoked by the layout manager) @Override public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { // create a new view View v = LayoutInflater.from(parent.getContext()) .inflate(R.layout.my_text_view, parent, false); // set the view's size, margins, paddings and layout parameters ... ViewHolder vh = new ViewHolder(v); return vh; } // Replace the contents of a view (invoked by the layout manager) @Override public void onBindViewHolder(ViewHolder holder, int position) { // - get element from your dataset at this position // - replace the contents of the view with that element holder.mTextView.setText(mDataset[position]); } // Return the size of your dataset (invoked by the layout manager) @Override public int getItemCount() { return mDataset.length; } }
CardView
CardView
extends the FrameLayout
class and lets you show information
inside cards that have a consistent look on any app. CardView
widgets can have
shadows and rounded corners.
To create a card with a shadow, use the android:elevation
attribute.
CardView
uses real elevation and dynamic shadows
and falls back to a programmatic shadow implementation on earlier versions. For more information,
see Compatibility.
Here's how to specify properties of CardView
:
- To set the corner radius in your layouts, use the
card_view:cardCornerRadius
attribute. - To set the corner radius in your code, use the
CardView.setRadius
method. - To set the background color of a card, use the
card_view:cardBackgroundColor
attribute.
To include a CardView
in your layout:
<!-- A CardView that contains a TextView --> <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto" android:id="@+id/card_view" android:layout_gravity="center" android:layout_width="200dp" android:layout_height="200dp" card_view:cardCornerRadius="4dp"> <TextView android:id="@+id/info_text" android:layout_width="match_parent" android:layout_height="match_parent" /> </android.support.v7.widget.CardView>