This page is based primarily on Kristin Marsicano, Brian Gardner, Bill Phillips, and Christ Stewart’s Android Programming: The Big Nerd Ranch Guide (2019).
Some High Level Things To Know
- Generally, Android apps are written in either Kotlin or Java.
- Android has lived over many versions, you can support the majority of Android devices by supporting Android 5.0+ (API Level 21+).
- Use Android Studio, built on JetBrains IDEA IDE, it is available free and bundles everything you’ll need to start developing.
- “An activity is responsible for managing user interaction with a screen of information.”
- Android provides the base Activity class, app classes will be sub-classes of this class.
- “A layout defines a set of UI objects and the objects’ positions on the screen. A layout is made up of definitions written in XML.”
- AndroidX (Jetpack) provides libraries one interacts with when developing.
- Historically this was provided as a single library, Jetpack does away with this model allowing individual libraries to be updated without requiring all libraries to be.
- Resources are non-code files and can include a variety of file types, including XML (which is used for layouts).
- Resources are kept in app/res
- Layouts are in /res/layout/
- String Files are in /res/values/
- Resources can be accessed using R.nameoftype.nameofresource.
- Usually divided into several “tool windows.” On the left is Project on the bottom is Build, and the main window is the Editor.
- Design/Text Views
- Design/Blueprint Preview
- Layout Decorations
- Build Tool
- When creating an activity use the extension .kt (convention).
- Layouts are named after the activity they work with in snake_case (convention).
- Classes are found in app/java, ignore the java naming, you can use Kotlin.
- “Views are the building blocks you use to compose a UI. Everything you see on the screen is a view. Views that the user can see or interact with are called widgets.”
- “Every widget is an instance of the View class or one of its subclasses (such as TextView or Button.”
- ViewGroups (aka layouts) are containers for other buttons and allow one to control how the contained views appear.
- Views within a ViewGroup are “children.”
- “Every widget has a corresponding XML element, and the name of the element is the type of the widget.”
- “Each element has a set of XML attributes. Each attribute is an instruction about how the widget should be configured.”
- View Hierarchy – A hierarchy of View objects in which widgets exist.
- Even your root view will have a parent, the view on Android in which the app lives.
- LinearLayout – To make views appear on a single row or column.
- Strings File – Where one keeps string resources (res/values/strings.xml), called using @string/nameofresource
Common Widget Attributes
- android:layout_width and android:layout_height
- match_parent makes the view as big as its parent.
- wrap_content makes view as big as needed to contain its content.
- android:orientation – Choose between vertical and horizontal alignment for children views.
- Inflate View: Activity.setContentView(layoutResID: Int)