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page.title=UI Widgets
@jd:body
<div id="qv-wrapper">
<div id="qv">
<h2>In this document</h2>
<ol>
<li><a href="#recyclerview">RecyclerView</a></li>
<li><a href="#cardview">CardView</a></li>
</ol>
</div>
</div>
<p>The support library in the Android L Developer Preview contains two new widgets,
<code>RecyclerView</code> and <code>CardView</code>. Use these widgets to show complex lists
and cards in your app. These widgets have material design styles and animations by default.</p>
<h2 id="recyclerview">RecyclerView</h2>
<p><code>RecyclerView</code> is a more advanced version of <code>ListView</code>. This widget is
a container for large sets of views that can be recycled and scrolled very efficiently. Use the
<code>RecyclerView</code> widget when you have lists with elements that change dynamically.</p>
<p><code>RecyclerView</code> is easy to use, because it provides:</p>
<ul>
<li>A set of layout managers for positioning items</li>
<li>Default animations for common item operations</li>
</ul>
<p>You also have the flexibility to define custom layout managers and animations for this
widget.</p>
<p>To use the <code>RecyclerView</code> widget, you have to specify an adapter and a layout
manager. An <strong>adapter</strong> provides a binding from a dataset to views that are displayed
within a <code>RecyclerView</code>. For example, if your dataset is an array of strings displayed
as <code>TextView</code> items, the layout manager asks the adapter to:
</p>
<ul>
<li>Set the text of an existing <code>TextView</code> to one of the strings in the dataset</li>
<li>Create new <code>TextView</code> objects</li>
<li>Determine the size of the dataset</li>
</ul>
<p>To create an adapter, you extend the <code>RecyclerView.Adapter</code> class. The details of
the implementation depend on the specifics of your dataset and the type of views. Fore more
information, see the examples below.</p>
<img src="/preview/material/images/RecyclerView.png" alt="" id="figure1" style="width:550px"/>
<p class="img-caption">
<strong>Figure 1</strong> - The <code>RecyclerView</code> widget.
</p>
<p>A <strong>layout manager</strong> positions item views inside a <code>RecyclerView</code> and
determines when to reuse item views that are no longer visible to the user. To reuse (or
<em>recycle</em>) 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
<code>findViewById</code> lookups.
</p>
<p><code>RecyclerView</code> provides two layout managers you can use:</p>
<ul>
<li><code>LinearLayoutManager</code> shows the items in a vertically scrolling list.</li>
<li><code>GridLayoutManager</code> shows the items in a rectangular grid.</li>
</ul>
<p>To create a custom layout, you extend the <code>RecyclerView.LayoutManager</code> class.</p>
<h3>Examples</h3>
<p>To include a <code>RecyclerView</code> in your layout:</p>
<pre>
<!-- 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"/>
</pre>
<p>To get the <code>RecyclerView</code> object in your activity:</p>
<pre>
public class MyActivity extends ActionBarActivity {
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 the size is fixed
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);
}
...
}
</pre>
<p>To create a simple adapter:</p>
<pre>
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 = new TextView(parent.getContext());
// 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;
}
}
</pre>
<h2 id="cardview">CardView</h2>
<p><code>CardView</code> extends the <code>FrameLayout</code> class and lets you show information
inside a card with optional rounded corners:</p>
<ul>
<li>To set the corner radius in your layouts, use the <code>android:cardCornerRadius</code>
attribute.</li>
<li>To set the corner radius in your code, use the <code>CardView.setRadius</code> method.</li>
</ul>
<p>To set the background color of a card, use the <code>android:cardBackgroundColor</code>
attribute.</p>
<p>To include a <code>CardView</code> in your layout:</p>
<pre>
<!-- A CardView that contains a TextView -->
<android.support.v7.widget.CardView
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>
</pre>
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