In /res/values/strings.xml:

<string-array name="spinner_options">
    <item>Option 1</item>
    <item>Option 2</item>
    <item>Option 3</item>
</string-array>

In layout XML:

<Spinner
    android:id="@+id/spinnerName"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:entries="@array/spinner_options" />

In Activity:

Spinner spinnerName = (Spinner) findViewById(R.id.spinnerName);
spinnerName.setOnItemSelectedListener(new OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
         String chosenOption = (String) parent.getItemAtPosition(position);
    }
    @Override
    public void onNothingSelected(AdapterView<?> parent) {}
});

Spinner It is a type of dropdown input. Firstly in layout

  <Spinner
    android:id="@+id/spinner"     <!-- id to refer this spinner from JAVA-->
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    
</Spinner>

Now Secondly populate values in spinner There are mainly two ways to populate values in spinner.

1. From XML itself create a array.xml in values directory under res. Create this array

  <string-array name="defaultValue">
    <item>--Select City Area--</item>
    <item>--Select City Area--</item>
    <item>--Select City Area--</item>
</string-array>

Now add this line in sppiner XML

            android:entries="@array/defaultValue"

2. You can also add values via JAVA

if you are using in activity cityArea = (Spinner) findViewById(R.id.cityArea); else if you are using in fragment

cityArea = (Spinner) findViewById(R.id.cityArea);

Now create a arrayList of Strings

ArrayList<String> area = new ArrayList<>();
//add values in area arrayList
cityArea.setAdapter(new ArrayAdapter<String>(context
                            , android.R.layout.simple_list_item_1, area));

This will look like

According to the device Android version it will render style

Following are some of the default themes

If an app does not explicitly request a theme in its manifest, Android System will determine the default theme based on the app’s targetSdkVersion to maintain the app’s original expectations:

Android SDK Version	Default Theme
Version < 11	@android:style/Theme
Version between 11 and 13	@android:style/Theme.Holo
14 and higher	@android:style/Theme.DeviceDefault

Spinner can be easily customized with the help of xml eg

 android:background="@drawable/spinner_background"

 android:layout_margin="16dp"

 android:padding="16dp"

Create a custom background in XML and use it.

easily get the position and other details of the selected item in spinner

cityArea.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            areaNo = position;
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    });

Change the text color of the selected item in spinner

This can be done in two ways in XML

<item android:state_activated="true" android:color="@color/red"/>

This will change the selected item color in the popup.

and from JAVA do this (in the setOnItemSelectedListener(...))

 @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                 ((TextView) parent.getChildAt(0)).setTextColor(0x00000000);
// similarly change `background color` etc.
            }