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page.title=Spinner
parent.title=Hello, Views
parent.link=index.html
@jd:body
<p>{@link android.widget.Spinner} is a widget similar to a drop-down list for selecting items.</p>
<p>In this tutorial, you'll create
a simple spinner widget that displays a list of planets. When one is selected, a toast message
will display the selected item.</p>
<ol>
<li>Start a new project named <em>HelloSpinner</em>.</li>
<li>Open the <code>res/layout/main.xml</code> file and insert the following:
<pre>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:padding="10dip"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
android:text="@string/planet_prompt"
/>
<Spinner
android:id="@+id/spinner"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:prompt="@string/planet_prompt"
/>
</LinearLayout>
</pre>
<p>Notice that the {@link android.widget.TextView}'s <code>android:text</code> attribute and the
{@link android.widget.Spinner}'s <code>android:prompt</code> attribute both reference the same
string resource. This text behaves as a title for the widget. When applied to the {@link
android.widget.Spinner}, the title text will appear
in the selection dialog that appears upon selecting the widget.</p>
</li>
<li>Create a <code>strings.xml</code> file in <code>res/values/</code> and edit the file to look
like this:
<pre>
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="planet_prompt">Choose a planet</string>
<string-array name="planets_array">
<item>Mercury</item>
<item>Venus</item>
<item>Earth</item>
<item>Mars</item>
<item>Jupiter</item>
<item>Saturn</item>
<item>Uranus</item>
<item>Neptune</item>
</string-array>
</resources>
</pre>
<p>The {@code <string>} element defines the title string referenced by the {@link
android.widget.TextView} and {@link android.widget.Spinner} in the layout above. The {@code
<string-array} element defines the list of strings that will be displayed as the list in
the {@link android.widget.Spinner} widget.</p>
</li>
<li>Now open the <code>HelloSpinner.java</code> file and insert the following code for the {@link
android.app.Activity#onCreate(Bundle) onCreate()} method:
<pre>
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Spinner spinner = (Spinner) findViewById(R.id.spinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.planets_array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
}
</pre>
<p>After the {@code main.xml} layout is set as the content view, the {@link
android.widget.Spinner} widget is captured from the layout with {@link
android.app.Activity#findViewById(int)}. The {@link
android.widget.ArrayAdapter#createFromResource(Context,int,int) createFromResource()} method then
creates a new {@link android.widget.ArrayAdapter}, which binds each item in the string array
to the initial appearance for the {@link android.widget.Spinner} (which is how each item will
appear in the spinner when selected). The {@code
R.array.planets_array} ID references the {@code string-array} defined above and the
{@code android.R.layout.simple_spinner_item} ID references a layout for the standard spinner
appearance, defined by the platform. Then {@link
android.widget.ArrayAdapter#setDropDownViewResource(int)} is called to define the appearance for
each item when the widget is opened ({@code simple_spinner_dropdown_item} is
another standard layout defined by the platform). Finally, the {@link android.widget.ArrayAdapter}
is set to associate all of its items with the {@link android.widget.Spinner} by calling {@link
android.widget.AdapterView#setAdapter(T)}.</p>
</li>
<li>Now create a nested class that implements {@link
android.widget.AdapterView.OnItemSelectedListener}. This will provide a callback method that will
notify your application when an item has been selected from the {@link
android.widget.Spinner}. Here's what this class should look like:
<pre>
public class MyOnItemSelectedListener implements OnItemSelectedListener {
public void onItemSelected(AdapterView<?> parent,
View view, int pos, long id) {
Toast.makeText(parent.getContext()), "The planet is " +
parent.getItemAtPosition(pos).toString(), Toast.LENGTH_LONG).show();
}
public void onNothingSelected(AdapterView<?> parent) {
// Do nothing.
}
}
</pre>
<p>The {@link android.widget.AdapterView.OnItemSelectedListener} requires the {@link
android.widget.AdapterView.OnItemSelectedListener#onItemSelected(AdapterView,View,int,long)
onItemSelected()} and {@link
android.widget.AdapterView.OnItemSelectedListener#onNothingSelected(AdapterView)
onNothingSelected()} callback methods. The former is called when an item from the {@link
android.widget.AdapterView} is selected, in which case, a short {@link android.widget.Toast}
message displays the selected text; and the latter is called when a selection disappears from the
{@link android.widget.AdapterView}, which doesn't happen in this case, so it's ignored.</p>
</li>
<li>Now the {@code MyOnItemSelectedListener} needs to be applied to the {@link
android.widget.Spinner}. Go back to the {@link android.app.Activity#onCreate(Bundle) onCreate()}
method and add the following line to the end:
<pre>
spinner.setOnItemSelectedListener(new MyOnItemSelectedListener());
</pre>
<p>This creates a new anonymous instance of the {@code MyOnItemSelectedListener} and sets it as the
listener for the {@link android.widget.Spinner}.</p>
</li>
<li>Run the application.</li>
</ol>
<p>It should look like this:</p>
<img src="images/hello-spinner.png" width="150px" />
<h3>Resources</h3>
<ul>
<li>{@link android.R.layout}</li>
<li>{@link android.widget.ArrayAdapter}</li>
<li>{@link android.widget.Spinner}</li>
</ul>
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