Spinner
is a widget similar to a drop-down list for selecting items.
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.
res/layout/main.xml
file and insert the following:
<?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>
Notice that the TextView
's android:text
attribute and the
Spinner
's android:prompt
attribute both reference the same
string resource. This text behaves as a title for the widget. When applied to the Spinner
, the title text will appear
in the selection dialog that appears upon selecting the widget.
strings.xml
file in res/values/
and edit the file to look
like this:
<?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>
The <string>
element defines the title string referenced by the TextView
and Spinner
in the layout above. The <string-array
element defines the list of strings that will be displayed as the list in
the Spinner
widget.
HelloSpinner.java
file and insert the following code for the onCreate()
method:
@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); }
After the main.xml
layout is set as the content view, the Spinner
widget is captured from the layout with findViewById(int)
. The createFromResource()
method then
creates a new ArrayAdapter
, which binds each item in the string array
to the initial appearance for the Spinner
(which is how each item will
appear in the spinner when selected). The R.array.planets_array
ID references the string-array
defined above and the
android.R.layout.simple_spinner_item
ID references a layout for the standard spinner
appearance, defined by the platform. Then setDropDownViewResource(int)
is called to define the appearance for
each item when the widget is opened (simple_spinner_dropdown_item
is
another standard layout defined by the platform). Finally, the ArrayAdapter
is set to associate all of its items with the Spinner
by calling setAdapter(T)
.
AdapterView.OnItemSelectedListener
. This will provide a callback method that will
notify your application when an item has been selected from the Spinner
. Here's what this class should look like:
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. } }
The AdapterView.OnItemSelectedListener
requires the onItemSelected()
and onNothingSelected()
callback methods. The former is called when an item from the AdapterView
is selected, in which case, a short Toast
message displays the selected text; and the latter is called when a selection disappears from the
AdapterView
, which doesn't happen in this case, so it's ignored.
MyOnItemSelectedListener
needs to be applied to the Spinner
. Go back to the onCreate()
method and add the following line to the end:
spinner.setOnItemSelectedListener(new MyOnItemSelectedListener());
This creates a new anonymous instance of the MyOnItemSelectedListener
and sets it as the
listener for the Spinner
.
It should look like this: