Android Tutorial

CHAPTER
17
Custom Components
Android offers a great list of pre-built widgets like Button, TextView, EditText, ListView, CheckBox,
RadioButton, Gallery, Spinner, AutoCompleteTextView etc. which you can use directly in your Android application
development, but there may be a situation when you are not satisfied with existing functionality of any of the
available widgets. Android provides you with means of creating your own custom components which you can
customized to suit your needs.
If you only need to make small adjustments to an existing widget or layout, you can simply subclass the widget or
layout and override its methods which will give you precise control over the appearance and function of a screen
element.
This tutorial explains you how to create custom Views and use them in your application using simple and easy
steps.
Creating a Simple Custom Component
The simplest way to create your custom component is to extend an existing widget class or subclass with your own
class if you want to extend the functionality of existing widget like Button, TextView, EditText, ListView, CheckBox
etc. otherwise you can do everything yourself by starting with theandroid.view.View class.
At its simplest form you will have to write your constructors corresponding to all the constructors of the base class.
For example if you are going to extend TextView to create a DateView then following three constructors will be
created for DateView class:
public class DateView extends TextView {
public DateView(Context context) {
}
super(context);
//--- Additional custom code --
public DateView(Context context, AttributeSet attrs) {
super(context, attrs);
//--- Additional custom code --
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