Introducing Android Views and Layouts Android

Before we go any further, we need to define a few terms. This gives you a better understanding of certain capabilities provided by the Android SDK before they are fully introduced. First, let’s talk about the View and what it is to the Android SDK.

Introducing the Android View

The Android SDK has a Java packaged named android.view. This package contains a number of interfaces and classes related to drawing on the screen. However, when we refer to the View object, we actually refer to only one of the classes within this package: the android.view.View class.

The View class is the basic user interface building block within Android. It represents a rectangular portion of the screen. The View class serves as the base class for nearly all the user interface controls and layouts within the Android SDK.

Introducing the Android Control

The Android SDK contains a Java package named android.widget. When we refer to controls, we are typically referring to a class within this package. The Android SDK includes classes to draw most common objects, including ImageView, FrameLayout, EditText, and Button classes. As mentioned previously, all controls are typically derived from the View class.

This chapter is primarily about controls that display and collect data from the user. We cover many of these basic controls in detail.

Introducing the Android Layout

One special type of control found within the android.widget package is called a layout. A layout control is still a View object, but it doesn’t actually draw anything specific on the screen. Instead, it is a parent container for organizing other controls (children). Layout controls determine how and where on the screen child controls are drawn. Each type of layout control draws its children using particular rules. For instance, the LinearLayout control draws its child controls in a single horizontal row or a single vertical column. Similarly, a TableLayout control displays each child control in tabular format (in cells within specific rows and columns).

In Chapter “Designing User Interfaces with Layouts,” we organize various controls within layouts and other containers. These special View controls, which are derived from the android.view.ViewGroup class, are useful only after you understand the various display controls these containers can hold. By necessity, we use some of the layout View objects within this chapter to illustrate how to use the controls previously mentioned. However, we don’t go into the details of the various layout types available as part of the Android SDK until the next chapter.


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