Lecture 3

Question 1

What are the four different types of components?

Answer 1

Activities - single screen

Services - background processes

Broadcast receivers - to subscribe to events in the android operating system

Content providers - e.g databases

Question 2

What is the point of a component?

Answer 2

Entry point through which the system or user can enter the app

Question 3

What are Intents?

Answer 3

Allows an app to call a component from another app

Question 4

What is an Activity?

Answer 4

Entry point for interacting with the user

Single screen with an interface

Can be launched by other apps is the containing app allows it

Question 5

What interactions between system and app do activities faciliate?

Answer 5

Tracking user activity (what they are doing)

Tracking previously used processes and content and allowing user to resume

Allowing apps to flow between each other

Question 6

What is the most important component type?

Answer 6

Activity

Question 7

When an Activity is launched, what processes are called?

Answer 7

onCreate() -> onStart() -> onResume()

Question 8

When is onPause() called?

Answer 8

When the activity needs to pause but still be visible, e.g. a semi transparent dialog or window covers it

Question 9

When a resumed activity is closed, what processes are called?

Answer 9

onPause() -> onStop() -> onDestroy()

Question 10

When is an activity stopped?

Answer 10

When another Activity is launched. E.g. new window or closing the app

Question 11

What happens to an Activity when the screen is rotated?

Answer 11

Activity is destroyed then Recreated

State of any view components is retrieved and re-instantiated though

Question 12

What 6 states can an Activity be in?

Answer 12

Created

Started (visible)

Resumed (visible)

Paused (partially visible)

Stopped (hidden)

Destroyed

Question 13

When should you save any important information?

Answer 13

Frequently and immediately if possible!

onPause and onStop should be used to save non-critical state info

Question 14

How do apps run with relation to the linux-like architecture of Android?

Answer 14

Each app is separate linux user with its own VM. Can only access its own files

Question 15

Which component doesn’t exchange Intents?

Answer 15

Content providers

Question 16

Why are intents used instead of direct method calls?

Answer 16

Allows other components to be started

access can be controlled by OS

Question 17

Where must all components be registered?

Answer 17

AndroidManifest.xml

Question 18

How do you start a new Activity?

Answer 18

Define a class that sub-classes Activity

Add some GUI control to invoke from parent Activity

Listen for the relevant GUI event, then launch a new Intent

Question 19

What are the two types of Intent? What’s the difference?

Answer 19

Explicit and Implicit

Explicit: specifies exactly which Activity should be started

Implicit: Explains what the activity should do (eg a web browser) - system then finds the most appropriate

Question 20

What is the back stack?

Answer 20

Collection of activities that users interact with

Each opened Activity is added to the back stack when it is opened

When the user presses the back button, the Activity is ended and popped off the stack

Question 21

How can you have multiple instances of the same activity within an app on the back stack?

Answer 21

if activities in that app can be instantiated from multiple places

Question 22

How can the back stack behaviour be modified?

Answer 22

Attributes in <activity> manifest element and flags in startActivity()</activity>

Can do things like clear back stack of all activities from that app except the root activity, or bring forward an existing activity