2.1 KiB
2.1 KiB
Activities
Subclasses of android.app.Activity
- Present a visual UI
- Each activity has its own 'window'
- Only one 'window' on screen at once
- Granular management of the resources of an application
- UI layout - a 'view'
- Specified in a separate XML file
- Constructed programmatically
- Apps usually have several activities
Android UI
An activity has a window associated with it - usually full screen.
View Hierarchy
There are 3 types of views:
- Those that display something (
Views) - Those that do something (
Widgets) - Those that lay out sub-views (
ViewGroups)
View Principles
Mobile devices are rarely the same, i.e. they have different screen sizes & resolutions
- Layout should adapt to the screen it is inflated in
- No hard-coding, layouts are defined in hierarchies and relationships.
- Different layouts for orientation
ViewGroups
- Frame Layout
- Simplest - contains a single object
- Linear Layout
- Aligns all children in a single direction
- Table Layout
- Positions children into columns and rows
- Constraint Layout
- Allows children to specify their position relative to their parent view
- Scroll View
- A vertical scrolling view; only contains a single element
Views Widgets
- Views that the user can optionally interact with
- Buttons, text view, calendar viewer, image viewer, etc.
- Generate UI events
Views Parameters
- width or height
- Use percentages - relative to parent or screen width, etc.
- ID
- Used to generate a Java member variable we can refer to within the program
- Basic binding of methods
- Used to automatically bind UI events to methods
Views Resources
- Layouts are an example of a resource
- Static content used by components at run-time
- Can be referenced by ID
Data Binding - involves a lot of boilerplate code
@{} notation - receives data changes
@={} - receives data changes to the property and listens to user updates
Model-View-ViewModel
The Manifest
A list of the application's components