UI

Question 1

Define each of the 4 core components of the UI…

Answer 1

View -> A rectangular area which acts as the building block for all Android UI’s. Everything in the Android UI is considered a View.
ViewGroup -> A container that holds and organises a selection of Views. ViewGroup is the base class for containers and layouts.
Widget -> A type of View that holds pre-build android UI elements. E.g Button, TextView.
Layout -> Defines the structure of a UI. Contains View and ViewGroup elements.

Question 2

What is the ViewGroup a base class for?

Answer 2

Layouts and Containers.

Question 3

Is a Layout a ViewGroup?

Answer 3

ViewGroups are often called layouts, as layouts are the most common type of ViewGroup. However, a ViewGroup refers to any type of contained View collection.

Question 4

Define an Adapter…

Answer 4

The mechanism responsible for pulling data from a source, populating views with the data, and returning the views to an AdapterView.
Acts as the bridge between the Data Source and the AdapterView.

Question 5

Define an AdapterView…

Answer 5

A ViewGroup that enables data to be displayed on screen. It binds to the Adapter, and calls the Adapters methods in order to be populated with the data.

Question 6

What are the most common children of AdapterView?

Answer 6

ListView and GridView.

Question 7

What are the 2 most common types of Adapters?

Answer 7

Array Adapter -> Pull data from XML.
Cursor Adapter -> Pull data from database.

Question 8

What are the 2 main responsibilities of an AdapterView?

Answer 8

Populate the layout with data through communication with the Adapter.

Handle touch events through the use of AdapterView.OnClickListener( )

Question 9

Give a brief, succinct summary of how an Adapter and AdapterView work and what their objective is…

Answer 9

An Adapter is used to populate an AdapterView. It does so by pulling data from a source and populating Views with the data. The Adapters methods can the be called by the AdapterView, and these methods return the populated and inflated Views to the AdapterView, which then displayed on the UI.

Question 10

What are the 2 types of menus? Define each…

Answer 10

Optional -> A global menu that contains the primary set of menu items for the application.
Context -> A local menu that appears on certain events such as a touch and hold. The menu that appears is relative to the View UI element that was interacted with.

Question 11

What are the 3 steps to create a menu?

Answer 11

1 - Define a menu resource in the XML with the menu items.
2 - Inflate the menu resource with the menu inflators ( onCreateOptionsMenu, onCreateContextMenu )
3 - Handle menu item selection ( onMenuItemSelected, onOptionsMenuItemSelected, onContextMenuItemSelected )

Question 12

What is RecyclerView?

Answer 12

A widget that is able to dynamically display data in a memory and time efficient way through the process of recycling ViewHolders.

Question 13

How does the RecyclerView conduct recycling?

Answer 13

When a ViewHolder exits the screen from the head, it is stored in a small cache, populated with new data via the adapter, and then brought back onto the screen from the tail end.
Vice verse when a ViewHolder exits the tail end (down scroll).

Question 14

What are the 2 computation benefits of using a RecyclerView?

Answer 14

Memory -> Only instantiates elements that are required on screen, thus reducing memory being used redundantly by instantiated but unused list items.
Time -> A reduction in number of elements populating the list at any one time improves scrolling responsiveness.

Question 15

In the context of a RecyclerView, what does the Adapter do?

Answer 15

For each data element, the adapter pulls data from the source, inflates ViewHolder layout and binds data to the ViewHolder Views.

Question 16

What are 4 main methods / class of the RecyclerView Adapter class? Define each and give the order that they are called in…

Answer 16

public static class MyViewHolder extends RecyclerView.ViewHolder –> ViewHolder object class that is instantiated. The constructor is passed the inflated view as an argument which can then be populated.

onCreateViewHolder -> Inflates the Views of the item layout xml, passes the View to a MyViewHolder instance in the retuirn statement.

onBindViewHolder -> Binds the data to the inflated ViewHolder. Takes in the MyViewHolder object that was returned by onCreateViewHolder.

getItemCount -> Returns the size of the list.

Question 17

For a RecyclerView, what is a LayoutManager?

Answer 17

Responsible for positioning items in the RecyclerView list.

Question 18

What are the 5 steps to create a RecyclerView?

Answer 18

1 - Add RecyclerView library to the app gradle file.
2 - Add a RecyclerView widget to the XML file.
3 - Create a layout XML file that defines the structure of each ViewHolder
4 - Create the Adapter
5 - In activity or fragment get a reference to the RecyclerView and set the Adapter and LayoutManager.

Question 19

What is a fragment? What hosts them?

Answer 19

Fragments are independent, dynamic UI’s within a subsection of the activity.
They are hosted by an activity.

Question 20

Define the 2 types of fragments…

Answer 20

Native -> Built into individual devices, thus reduces application portability.
Support -> Built into the android library in the application, that ensures application portability across devices.

Question 21

What are all Fragment activity lifecycle call backs public?

Answer 21

So the hosting activity has access to them.

Question 22

What are the 11 call back methods?

Answer 22

onAttach, onCreate, onCreateView, onActivityCreated, onStart, onResume, onPause, onStop, onDestroyView, onDestroy, onDetach.

Question 23

Define each of the Fragment lifecycle call back methods…

Answer 23

TBD…

Question 24

What does DP and SP stand for?

Answer 24

Device Independent Pixel and Scalable Pixel.

Question 25

Define a widget…

Answer 25

A pre-define View provided by Android.

Question 26

What data structure does a Recycler View to hold re-usable Views?

Answer 26

Queue.

Question 27

What are the 4 components needed to create a Recycler View?

Answer 27

Data
Adapter
RecyclerView
LayoutManager

Question 28

What are the problems with AdapterViews that the RecyclerView solves?

Answer 28

Memory inefficient -> All data is pulled and instantiated on load, regardless of whether they are on screen. Leads to unnecessary memory allocation.
Performance inefficient -> All data is instantiated and has OnItemSelected implemented. On large data sets this is computationally expensive and can lead to performance delay.

Question 29

How does RecyclerView resolve the issues of AdapterView?

Answer 29

Memory Efficient -> Only pulls data and instantiates ViewHolders for what is needed on screen. Only a small number of ViewHolders are kept off screen in the Queue.
Performance Efficient -> User interaction capability is only implemented for the items on screen.