`LiveData`

An observable data holder class that is lifecycle aware. - It holds data, and is designed to serve as a wrapper for any type of data - It is observable, so another class can sign up to be notified when the data being held changes - It is lifecycle-aware. When a class signs up to observe LiveData, it is associated with a LifecycleOwner. The LiveData then only updates observers that are in an active lifecycle state.

MutableLiveData

The mutable version of LiveData. Because LiveData is an object, when we want to access the data that is being stored, use the value property of the LiveData. Common practices recommend having a MutableLiveData backing object, with a public LiveData

private val _word = MutableLiveData<String>()
val word: LiveData<String>
    get() = _word
//...
fun ...(){
    _word.value = "..."
}

Attaching an observer

    viewModel.word.observe(viewLifecycleOwner) { newValue -> {}}

• viewLifecycleOwner is how the LiveData is aware of the lifecycle state of the view, and is inherited from the Activity/Fragment
• The second parameter is a lambda that provides the updated value for whatever logic it is you wanted to do with it.

Data Binding

Allows you to access LiveData objects directly in the .xml view files. The root element of the view you want to use data binding in should be a <layout> and should also contain a <data> element before the body of the view. In the class that corresponds to the view, inflate it using the DataBindingUtil.inflate() method.

Inside the <data> tag, include <variable> tags that you then initialize inside the onViewCreated callback of the associated class. Be sure to also provide the binding with the lifecycleOwner, so that it can observe LiveData correctly.

<data>
    <variable
        name="max"
        type="int" />
</data>

override fun onViewCreated(...){
    ...
    binding.max = ...
    binding.lifecycleOwner = viewLifecycleOwner
}

Once you have done that, you can reference those variables inside the rest of your xml view using binding expressions

<TextView 
    ...
    android:text="@{viewModel.name}" />