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