Data binding with ViewModel and LiveData

官方Demo

https://developer.android.com/codelabs/kotlin-android-training-live-data-data-binding#0

本文基于 ViewModel + LiveData 改造

Gradle配置

android {
    buildFeatures {
        dataBinding true
    }
}

Add ViewModel data binding

<layout ...>
   <data>
       <variable
           name="scoreViewModel"
           type="com.example.android.guesstheword.screens.score.ScoreViewModel" />
   </data>
   <androidx.constraintlayout.widget.ConstraintLayout

Button点击事件

<Button
   android:id="@+id/play_again_button"
   ...
   android:onClick="@{() -> scoreViewModel.onPlayAgain()}"
   ... />

Fragment中用DataBindingUtil初始化binding

override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View? {
        // Inflate view and obtain an instance of the binding class.
        val binding: ScoreFragmentBinding = DataBindingUtil.inflate(
                inflater,
                R.layout.score_fragment,
                container,
                false
        )
        return binding.root
    }

在Fragment中初始化binding.scoreViewModel

viewModelFactory = ScoreViewModelFactory(ScoreFragmentArgs.fromBundle(arguments!!).score)
viewModel = ViewModelProvider(this, viewModelFactory).get(ScoreViewModel::class.java)
//initial 
binding.scoreViewModel = viewModel

Add LiveData to data binding

XML配置

<TextView
   android:id="@+id/word_text"
   ...
   android:text="@{gameViewModel.word}"
   ... />

Fragment修改

set the fragment view as the lifecycle owner of the binding variable

binding.gameViewModel = ...
// Specify the fragment view as the lifecycle owner of the binding.
// This is used so that the binding can observe LiveData updates
binding.lifecycleOwner = viewLifecycleOwner

Add string formatting with data binding

strings.xml

<string name="quote_format">\"%s\"</string>
<string name="score_format">Current Score: %d</string>

layout.xml

<TextView
   android:id="@+id/word_text"
   ...
   android:text="@{@string/quote_format(gameViewModel.word)}"
   ... />

<TextView
   android:id="@+id/score_text"
   ...
   android:text="@{@string/score_format(gameViewModel.score)}"
   ... />