01 Android Layouts and XML

Question 1

Android apps are divided into two parts

Answer 1

1. Resources

2. Java code

Question 2

Resources include

Answer 2

● Layouts (define structure of UIs) 
● Drawables
      o graphics such as PNGs 
      o XML files that describe how to draw Shapes
● Strings 
● Colors 
● Menus 
● Styles (sort of like CSS) 
● Other miscellaneous things

Question 3

Java Code

Answer 3

● All the logic that runs
● Code you write
● Code you get from the Framework

Question 4

Layouts and Views

Answer 4

Every UI “widget” in Android is called a View Views can be “singular”
Buttons, TextViews, Checkboxes, etc
- Views can also be used to lay out other views
● Called “ViewGroups”
● Have child views
● Each ViewGroup has different rules for
organizing its children

Question 5

Other Info on the Layout

Answer 5

match_parent == Make me as big as the thing I’m inside. If I’m the top-most thing, make me as big as the screen
wrap_content == Make me only as big as the stuff I am displaying 60dp == Make me exactly 60 units big*
Dp = Density Independent Pixels (more on density later) * Assuming there is enough space

Question 6

android:id=”@+id/my_label”

Answer 6

@ Put this in the “id” group
+ Create a new one if it doesn’t exist my_label The name of the id.
On the Java side, this becomes: R.id.my_label

Question 7

Finding and Using Views in Java

Answer 7

In an Activity
TextView myText =
(TextView)findViewById(R.id.label)
In Fragments, or if you have a ViewGroup and want to find its children
Button button =
(Button)findViewById(R.id.my_button)

• The cast to Button or TextView is needed
because the declared return type is View
• FindViewByID is slow, so it is best to do it
once for each control in the onCreate
function, and never again

Question 8

Inflating Resources

Answer 8

Each screen in an Android app implemented using a Java class called an Activity*

When an Activity is created, you tell the Android SDK which layout file to use

The conversion from XML to Java is called “inflating”

Question 9

Inflating Resources (resource id)

Answer 9

Whenever your app needs to create UI, your Java code specifies what layout to use by providing a layout “resource Id”

R.layout.activity_main

R = Your app's resources 
layout = pick something in the "layout" folder(s) 
activity_main = The name of the layout

Question 10

Inflating Resources (layout file)

Answer 10

Choices, choices... Android automatically picks the layout file that best fits the "current configuration" of the device 
● Landscape vs. Portrait 
● Language 
● Screen Size 
● Screen Density*

Question 11

Inflating Resources (name, structure)

Answer 11

All resources are assigned an ID

Multiple versions of a resource can exist

Structured according to the type/folder the resource is in

Anything with the same name, but in different folders, get assigned the same ID

Question 12

Creating Views in Java

Answer 12

Its possible (but usually not recommended) to create Views directly in Java

You have to manually code each device configuration

LayoutParams are a pain

Question 13

Beginner Views to Know

Answer 13

TextView 
EditText 
Button 
FrameLayout 
LinearLayout 
RelativeLayout (Lab 1) 
ScrollView / HorizontalScrollView