[main]: Add mdp to lecture notes

docs/lectures/mdp/03_activities.md

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+# 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.
+
+![img](img/k.png)
+
+#### View Hierarchy
+
+There are 3 types of views:
+
+1. Those that display something (`Views`)
+2. Those that do something (`Widgets`)
+3. 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
+
+![img](img/l.png)
+
+## The Manifest
+
+A *list* of the application's components