Data Binding

Question 1

What is the syntax for assigning the current Activity as the binding’s lifecycleOwner?

Answer 1

binding.lifecycleOwner = this

Question 2

Why does a binding need a lifecycleOwner?

Answer 2

So that it knows when to start / stop looking for updates to LiveData properties

Question 3

Which 2 parameters are passed to the LiveData.observe function?

Answer 3

lifecycleOwner

Observer function - called whenever the LiveData property is updated

Question 4

What is the “fully qualified” name of a class?

Answer 4

com.example.appname.packagename.classname

Question 5

What needs to be added to the layout xml to use data binding through it?

What needs to be added to the Fragment for this to work?

Answer 5

A parent ^layout^ tag
A  ^data^ tag
A  ^variable^ tag within the ^data^  tag
Properties for the  ^variable^ tag
  name="my_name"
  type="fullyqualifiedclassname"

in Fragment.onCreateView( ):
binding.my_name = viewModel / LiveData / whatever represents this binding object in the Fragment

Question 6

What kind of class is usually passed into the tag when data binding via the xml layout?

Answer 6

A data class representing an entity

Question 7

What is the shortcut for setting a layout xml up for data binding?

Answer 7

Quick fix menu (intention menu) on the current root layout (usually ConstraintLayout)
– Convert to data binding layout

Question 8

Which class is automatically built when data binding has been added to a layout xml?
What class does this extend?

Answer 8

MyLayoutXmlBinding is generated

It extends ViewDataBinding.java

Question 9

What does (Generated)ViewDataBinding.root return?

Answer 9

The parent layout of the data-bound layout xml (usually a ConstraintLayout)

Question 10

What does Transformations.map() do?

Answer 10

Takes a LiveData and a lambda
Uses the lambda on the LiveData
Returns a new LiveData (of any type)

Question 11

What is the role of @BindingAdapters?

Answer 11

Annotation is applied to extension methods that sit between a view and bound data to provide custom behaviour when the data changes.
Can be used as an alternative to a LiveData Observer (?)

Question 12

What is the syntax for defining an @BindingAdapter function?

Answer 12

@BindingAdapter(“functionIdentifier”) // for use in xml
View.manipulateValuesForView(item: Entity) {
viewProperty = manipulationOfEntity(item)
}

Question 13

What is the purpose of a binding object?

Answer 13

Once a binding object has been created for your app, you can access the views, and other data, through the binding object, without having to traverse the view hierarchy or search for the data (using findViewById( )).

Question 14

How is data binding enabled? (3 different places)

Answer 14

1. In build.gradle(Module)

buildFeatures {
dataBinding true
}

2. Wrap your xml root layout in a ^layout^ tag
3. In the Fragment, add EITHER
   private lateinit var binding: ActivityMainBinding
   AND in onCreate( )
   binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
   OR in Fragment.onCreateView( )
   val binding = FragmentOverviewBinding.inflate(inflater)

Now, instead of using findViewById, all views can be referenced by using binding.viewId
OR
binding.apply{
  viewId1 // do something
  viewId2 // do something
}

Question 15

1. How do you refer to a data bound object and its attributes in the xml?
2. What is the syntax for accessing the object to assign to an xml attribute?

Answer 15

1. add a ^data^ tag with a ^variable
   name = “objectName”
   type=”fully_qualified_class_name”
2. access the attribute using “@={objectName.attribute}”

Question 16

What is the function that can be used to force a refresh of all binding expressions?

Answer 16

binding.invalidateAll( )

Question 17

When using a binding object, what must always be done in Fragment.onCreateView( ) after the binding object has been instantiated?

Answer 17

binding. lifecycleOwner = this

binding. viewModelXmlName = viewModel