Spinner

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last updated: 2018-02

Spinner is a widget that presents a drop-down list for selecting items. This guide explains how to create a simple app that displays a list of choices in a Spinner, followed by modifications that display other values associated with the selected choice.

Basic Spinner

In the first part of this tutorial, you'll create a simple spinner widget that displays a list of planets. When a planet is selected, a toast message displays the selected item:

Example screenshots of HelloSpinner app

Start a new project named HelloSpinner.

Open Resources/Layout/Main.axml and insert the following XML:

<?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.

Edit Resources/Values/Strings.xml and modify the file to look like this:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">HelloSpinner</string>
  <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 second <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.

Now open MainActivity.cs and add the following using statement:

using System;

Next, insert the following code for the OnCreate() method:

protected override void OnCreate (Bundle bundle)
{
    base.OnCreate (bundle);

    // Set our view from the "Main" layout resource
    SetContentView (Resource.Layout.Main);

    Spinner spinner = FindViewById<Spinner> (Resource.Id.spinner);

    spinner.ItemSelected += new EventHandler<AdapterView.ItemSelectedEventArgs> (spinner_ItemSelected);
    var adapter = ArrayAdapter.CreateFromResource (
            this, Resource.Array.planets_array, Android.Resource.Layout.SimpleSpinnerItem);

    adapter.SetDropDownViewResource (Android.Resource.Layout.SimpleSpinnerDropDownItem);
    spinner.Adapter = adapter;
}

After the Main.axml 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 Resource.Array.planets_array ID references the string-array defined above and the Android.Resource.Layout.SimpleSpinnerItem ID references a layout for the standard spinner appearance, defined by the platform. SetDropDownViewResource is called to define the appearance for each item when the widget is opened. Finally, the ArrayAdapter is set to associate all of its items with the Spinner by setting the Adapter property.

Now provide a callback method that notifys the application when an item has been selected from the Spinner. Here's what this method should look like:

private void spinner_ItemSelected (object sender, AdapterView.ItemSelectedEventArgs e)
{
    Spinner spinner = (Spinner)sender;
    string toast = string.Format ("The planet is {0}", spinner.GetItemAtPosition (e.Position));
    Toast.MakeText (this, toast, ToastLength.Long).Show ();
}

When an item is selected, the sender is cast to a Spinner so that items can be accessed. Using the Position property on the ItemEventArgs, you can find out the text of the selected object, and use it to display a Toast.

Run the application; it should look like this:

Screenshot example of Spinner with Mars selected as the planet

Spinner Using Key/Value Pairs

Often it is necessary to use Spinner to display key values that are associated with some kind of data used by your app. Because Spinner does not work directly with key/value pairs, you must store the key/value pair separately, populate the Spinner with key values, then use the position of the selected key in the Spinner to look up the associated data value.

In the following steps, the HelloSpinner app is modified to display the mean temperature for the selected planet:

Add the following using statement to MainActivity.cs:

using System.Collections.Generic;

Add the following instance variable to the MainActivity class. This list will hold key/value pairs for the planets and their mean temperatures:

private List<KeyValuePair<string, string>> planets;

In the OnCreate method, add the following code before adapter is declared:

planets = new List<KeyValuePair<string, string>>
{
    new KeyValuePair<string, string>("Mercury", "167 degrees C"),
    new KeyValuePair<string, string>("Venus", "464 degrees C"),
    new KeyValuePair<string, string>("Earth", "15 degrees C"),
    new KeyValuePair<string, string>("Mars", "-65 degrees C"),
    new KeyValuePair<string, string>("Jupiter" , "-110 degrees C"),
    new KeyValuePair<string, string>("Saturn", "-140 degrees C"),
    new KeyValuePair<string, string>("Uranus", "-195 degrees C"),
    new KeyValuePair<string, string>("Neptune", "-200 degrees C")
};

This code creates a simple store for planets and their associated mean temperatures. (In a real-world app, a database is typically used to store keys and their associated data.)

Immediately after the above code, add the following lines to extract the keys and put them into a list (in order):

List<string> planetNames = new List<string>();
foreach (var item in planets)
    planetNames.Add (item.Key);

Pass this list to the ArrayAdapter constructor (instead of the planets_array resource):

var adapter = new ArrayAdapter<string>(this,
    Android.Resource.Layout.SimpleSpinnerItem, planetNames);

Modify spinner_ItemSelected so that the selected position is used to look up the value (the temperature) associated with the selected planet:

private void spinner_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)
{
    Spinner spinner = (Spinner)sender;
    string toast = string.Format("The mean temperature for planet {0} is {1}",
        spinner.GetItemAtPosition(e.Position), planets[e.Position].Value);
    Toast.MakeText(this, toast, ToastLength.Long).Show();
}

Run the application; the toast should look like this:

Example of planet selection displaying temperature

Resources

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

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