Android

Question 1

What are the greatest challenges of Android development?

Answer 1

Multiple screen sizes and resolutions
Performance: make your apps responsive and smooth (ex. services when needed, to save battery)
Security: keep source code and user data safe
Compatibility: run well on older platform versions
Marketing: understand the market and your users

Question 2

Not a question! Read the metaphor:

“Think of Android as a hotel”

Answer 2

Your app is the guest
The Android System is the hotel manager
Services are available when you request them (intents)
In the foreground (activities) such as registration
In the background (services) such as laundry
Calls you when a package has arrived (broadcast receiver)
Access the city’s tour companies (content provider)

Question 3

Which are App building blocks?

Answer 3

Resources: layouts, images, strings, colors as XML and media files
Components: activities, services, …, and helper classes as Java code
Manifest: information about app for the runtime
Build configuration: APK versions in Gradle config files

Question 4

What component types does Android have?

Answer 4

Activity is a single screen with a user interface
Service performs long-running tasks in background
Content provider manages shared set of data
Broadcast receiver responds to system-wide announcements

Question 5

What do you know about MVP architecture pattern

Answer 5

The MVP- well-established way to group app functions:
- Views. Views are user interface elements that display data and respond to user actions. Every element of the screen is a view. The Android system provides many different kinds of views.

• Presenters. Presenters connect the application’s views to the model. They supply the views with data as specified by the model, and also provide the model with user input from the view.
• Model. The model specifies the structure of the app’s data and the code to access and manipulate the data.

Question 6

What ways of Creating and Laying out views do you know?

Answer 6

Graphically within Android Studio
XML Files
Programmatically

Question 7

What is view?

Answer 7

basic building block for user interface components

Question 8

View vs ViewGroup vs Layouts

Answer 8

View is the base class for widgets, it is an object that draws something on the screen that the user can interact with. (buttons, text fields, etc.).

Views can be grouped together inside a view group (ViewGroup), which acts as a container of views. The relationship is parent-child, (ScrollView, RecyclerView)

Some ViewGroups are designated as layouts because they organize child views in a specific way and are typically used as the root view group.
» LinearLayout: A group of child views positioned and aligned horizontally or vertically.
» RelativeLayout: each child view is positioned relative to other views
» TableLayout: child views arranged into rows and columns.
» AbsoluteLayout: A group that lets you specify exact locations (x/y coordinates) of its child views. Absolute layouts are less flexible and harder to maintain
» FrameLayout: child views are drawn in a stack, with the most recently added child on top. The size of the FrameLayout is the size of its largest child view.
» GridLayout: A group that places its child screens in a rectangular grid that can be scrolled.

Question 9

How is user interface build in Android?

Answer 9

All user interface elements in an Android app are built using View and ViewGroup objects. A View is an object that draws something on the screen that the user can interact with. A ViewGroup is an object that holds other View (and ViewGroup) objects in order to define the layout of the interface.

Question 10

What are the common operations you can do with Views?

Answer 10

Set properties: for example setting the text of a TextView.
Set focus: To force focus to a specific view, call requestFocus().
Set up listeners: Views allow clients to set listeners that will be notified when something interesting happens to the view.
Set visibility: You can hide or show views using setVisibility(int)

Question 11

What happens when you load a layout resource in your app?

Answer 11

When you load a layout resource in your app, Android initializes each node of the layout into a runtime object you can use to define additional behaviors, query the object state, or modify the layout.

Question 12

What is the ID view?

Structure of it.

Answer 12

Views may have an integer id associated with them
Are used to find specific views within the view tree

View IDs need not be unique throughout the tree, but it is good practice to ensure that they are at least unique within the part of the tree you are searching.

@[+][package:]type/name
TO ADD : android:id=”@+id/my_button”
+id means new id must be created and added to our resources (in the R.java file).
TO REFERENCE: android:id=”@android:id/empty”

With the android package namespace in place, we’re now referencing an ID from the android.R resources class, rather than the local resources class.
*@ - at-symbol

Question 13

Geometry of a View (location, dimension, unit)

Answer 13

The geometry of a view is that of a rectangle. A view has a location, expressed as a pair of left and top coordinates, and two dimensions, expressed as a width and a height. The unit for location and dimensions is the pixel.

Question 14

Accessing Resources
Structure of resource ID
How can we access

Answer 14

When your application is compiled, aapt generates the R class, which contains resource IDs for all the resources in your res/ directory. For each type of resource, there is an R subclass (for example, R.drawable for all drawable resources), and for each resource of that type, there is a static integer (for example, R.drawable.icon). This integer is the resource ID that you can use to retrieve your resource.

Structure:
type(string, drawable, layout) +
name(filename, string resource)

How can access:

• • In code: Using a static integer from a sub-class of your R class, such as: R.string.hello
• • In XML: @string/hello
• string is the resource type and hello is the resource name.

Question 15

Referencing style attributes - attr

Answer 15

A style attribute resource allows you to reference the value of an attribute in the currently-applied theme.

To reference a style attribute, the name syntax is almost identical to the normal resource format, but instead of the at-symbol (@), use a question-mark (?), and the resource type portion is optional. For instance:

?[:][/]

For ex, can reference an attribute to set the text color to match the “primary” text color of the system theme:
android:textColor=”?android:textColorSecondary”

explicitly would be: “?android:attr/textColorSecondary”

Question 16

Context Definition.

Typical uses of context:

Answer 16

= current state of the application/object. It lets newly-created objects understand what has been going on.

Typical uses of context:
Loading a resource. (getString, getColor)
Launching a new activity. (startActivity)
Creating views.
obtaining system service (regarding content providers, broadcasts, intent)

Question 17

Application Context Activity Context

Answer 17

They are both instances of Context, but the application instance is tied to the lifecycle of the application, while the Activity instance is tied to the lifecycle of an Activity. The activity is simply providing the context needed by the view. Thus, they have access to different information about the application environment.

Example Use: If you have to create an object whose lifecycle is attached to an activity, you can use the activity context.

Get the context:
Context context = getApplicationContext();

An activity is its own context:
TextView myText = new TextView(this);

Question 18

Ways to get Context

Answer 18

You can get the context by invoking

• — getApplicationContext(),
• — getContext(),
• — getBaseContext()
• — this (when in a class that extends from Context, such as the Application, Activity, Service and IntentService classes).

Question 19

Resource files

• Accesing Resource files
• Resource qualifiers

Answer 19

Resource files are stored in folders located in the res folder, including:
> drawable: For images and icons
> layout: For layout resource files
> menu: For menu items
> mipmap: For pre-calculated, optimized collections of app icons used by the Launcher
> values: For colors, dimensions, strings, and styles (theme attributes)

Question 20

dp , sp, px

Answer 20

• Device Independent Pixels (dp) - for Views
  - Scale Independent Pixels (sp) - for text
  Don’t use device-dependent units:
  - Actual Pixels (px)

Device-independent pixels (dp) are independent of screen resolution (used for views)
For example, 10px (10 fixed pixels) will look a lot smaller on a higher resolution screen, but Android will scale 10dp (10 device-independent pixels) to look right on different resolution screens.
Text sizes can also be set to look right on different resolution screens using scaled-pixel (sp) sizes.

Question 21

Style

Answer 21

A style is a resource that specifies common attributes such as height, padding, font color, font size, background color

Question 22

Responding to view clicks

Answer 22

1. Add clickListener to button
2. android:onClick=”showToast”

showToast() method must be public, return void, and require a view parameter in order to know which view called the method.

Question 23

Events, Event Handlers, Listener

Answer 23

Event : Something that happens
In UI: Click, tap, drag
Device: DetectedActivity such as walking, driving, tilting
Events are “noticed” by the Android system

Event Handlers: Methods that do something in response to a event
When the button itself will handle its touch event
Ex. in a custom button class, override: onTouchEvent(…)

Listener: if you want your activity to handle when someone touches the button, you use an event listener
btn.setOnTouchListener(…)

Question 24

String Resources - String, String array, Quantity Strings

Answer 24

String- XML resource that provides a single string.
text_string can include styling tags (format, html tags b,i,u)
text_string

String Array- XML resource that provides an array of strings.

    text_string

Quantity Strings (Plurals)- XML resource that carries different strings for pluralization

    Znaleziono %d piosenkę.
    Znaleziono %d piosenki.
    Znaleziono %d piosenek.

*quantity=[“zero” | “one” | “two” | “few” | “many” | “other”]

Question 25

Strong / Weak reference

Answer 25

A strong reference is an ordinary Java reference, the kind you use every day. For example, the code:
StringBuffer buffer = new StringBuffer();
As you don't want the garbage collector destroying objects you're working on, this is normally exactly what you want.

Aweak reference - is a reference that isn’t strong enough to force an object to remain in memory.
So you may find (if there are no strong references to the widget) thatweakWidget.get()suddenly starts returningnull.

Question 26

Style - Theme

Answer 26

So the difference is style attribute applies for just this view, theme – for this view and all its children.

Question 27

Manifest

Answer 27

1) application: Info about application (package,title, icon and theme) Also acts as a container that includes the Activity, Service, Content Provider and Broadcast Receiver tags for specifying the application components
- Node activity
name: class name
intent-filter : child tags which specify which
Intents launch the activity.
- Node service
- Node provider - content provider
- Node receiver - to register broadcasst receiver

2) uses-permission - the permissions you include will always be presented to the user to either grant or deny during installation. Ex. location services, SMS, internet