Android Widget Tutorial: Learning the Basics

androidwidgettutorialOne of the things that historically set the Android operating system apart from competitors such as iOS is the ability to create interactive app widgets that display in other applications such as the home screen.

An Android app widget is a miniature application window designed to be embedded in other applications. These widgets can receive periodic updates such as RSS feeds, weather updates, and news articles. Most Android users expect their favorite applications to provide a widget for quick and easy access to information they need. As an Android app developer, it is your job to understand what a widget is and how you can implement them into your existing and future development projects. Android Development for Beginners offers two comprehensive sections specifically about creating attractive app widgets.

If you are just starting out with Android development, consider checking out Java Essentials for Android before learning how to create your own app widgets. Since Android is based on the Java programming language, this course gives you the Java skills you need to succeed as an Android app developer.

Although widgets can be used for just about any purpose imaginable, it’s important to remember that widgets constantly refreshing data will use battery life and consume data for those users on limited bandwidth mobile data plans. Please keep these factors in mind while you are creating widgets as your users will not be very happy if they get an unexpectedly large cellular bill or if their battery life decreases significantly after installing your widget.

Android Widget Details

When you’re first starting out, the easiest way to publish a widget is using an App Widget provider. As you advance, you can also create your own App Widget Host designed to host other app widgets.

To create an App Widget, you need:

AppWidgetProviderInfo object – This describes the metadata for your app widget including such details as the app widget’s layout, update frequency, and the AppWidgetProvider class. All of this information should be defined using XML. To learn more about using XML, check out Android App Development Fundamentals.

AppWidgetProvider class implementation – This class describes the basic methods for interfacing with your app widget. Using the App Widget Provider, you are able to receive broadcasts when the widget is updated, enabled, disabled and deleted.

View Layout – Using XML, you can define the initial layout of your widget.

Many modern widgets also use the optional App Widget Configuration Activity. This optional activity allows users to modify certain settings within the widget when it is created. A good example of this is when  many of the popular weather widgets allow users to choose what locations they wish to receive weather updates about when they add the widget to their home screen.

It’s also important to take into account the size of your widget. Each widget will take up a certain amount of space on the user’s home screen. As a general rule, you should define the size of your widget with the following formula:

((Number of columns / rows) * 74) – 2

This formula allows you to create widget sizes that are device independent. By subtracting 2 at the end, you avoid any rounding issues that could occur depending on the device your widget is being installed on.

Widgets can also be resized by users if you enable this feature in the XML configuration file for your widget. Adding “android: resizeMode=”horizontal | vertical” will allow users to resize the widgets to fit alongside other widgets and app icons they may have on their home screen already.

Although you can create just a widget that uses a configuration activity for users to access it in the App Launcher, most widgets will be an extension of existing applications. The first step is to declare your widget in the Android Manifest. To do this, simply add the following XML code to your existing AndroidManifest.xml file:

<receiver android:name=”ExampleAppWidgetProvider” >

<intent-filter>

    <action android:name=”android.appwidget.action.APPWIDGET_UPDATE” />

</intent-filter>

<meta-data android:name=”android.appwidget.provider”

              android:resource=”@xml/example_appwidget_info” />

</receiver>

This lets the Android OS know that this application uses an App Widget Provider to implement a widget if the user decides to use it. If the above code looks foreign to you, Android Programming I explains how to create an Android Manifest file correctly.

One final thing you should know about widgets is a cool new feature that has been added as of the Android 4.2 release. You can now launch your application widgets on the lock screen of an android device. All you need to do is declare support for the “key guard” category within the AppWidgetProviderInfo XML file. For example:

<appwidget-provider xmlns:android=”http://schemas.android.com/apk/res/android”

android:widgetCategory=”keyguard|home_screen”

 …

>

</appwidget-provider>

Adding this code allows your widget to be placed on either the user’s home screen, lock screen, or both as the user chooses. This is a great new feature that can make your application stand out as a superior choice compared to many other widgets that have not yet adopted the lock screen property.

If you are using a game engine to create your Android applications such as GameSalad, much of the behind-the-scenes work relating to creating application widgets is already done for you. If you are unfamiliar with using GameSalad to create Android applications, you can learn more about it in Introduction to Mobile Games Development.

Of course, you can also code your applications and associated widgets by hand but if you are relatively new to Android, this can become a seemingly overwhelming task. As with any programming platform, practice is the only way to become more comfortable with using Android widgets appropriately. If you already have existing applications available in the Google Play Store, consider updating them with widget functionality – your users will appreciate it.

If you are still creating your very first android application, don’t forget to include at least one useful widget as it greatly increases the sense of value inherent to your application and teaches you a lot in the process!