Android 数据绑定

$ git clone https://github.com/android/codelab-android-databinding

android {
...
    buildFeatures {
       dataBinding true
    }
}

<layout xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools">
   <data>

   </data>
   <androidx.constraintlayout.widget.ConstraintLayout
           android:layout_width="match_parent"
           android:layout_height="match_parent">

       <TextView
...

// Some examples of complex layout expressions
android:text="@{String.valueOf(index + 1)}"
android:visibility="@{age < 13 ? View.GONE : View.VISIBLE}"
android:transitionName='@{"image_" + id}'

// Bind the name property of the viewmodel to the text attribute
android:text="@{viewmodel.name}"
// Bind the nameVisible property of the viewmodel to the visibility attribute
android:visibility="@{viewmodel.nameVisible}"
// Call the onLike() method on the viewmodel when the View is clicked.
android:onClick="@{() -> viewmodel.onLike()}"

    <data>
        <variable name="name" type="String"/>
        <variable name="lastName" type="String"/>
    </data>

        <TextView
                android:id="@+id/plain_name"
                android:text="@{name}" 
        ... />

        <TextView
                android:id="@+id/plain_lastname"
                android:text="@{lastName}"
        ... />

setContentView(R.layout.plain_activity)

val binding : PlainActivityBinding =
    DataBindingUtil.setContentView(this, R.layout.plain_activity)

    binding.name = "Your name"
    binding.lastName = "Your last name"

    <data>
        <variable
                name="viewmodel"
                type="com.example.android.databinding.basicsample.data.SimpleViewModel"/>
    </data>

        <TextView
                android:id="@+id/plain_name"
                android:text="@{viewmodel.name}"
... />
        <TextView
                android:id="@+id/plain_lastname"
                android:text="@{viewmodel.lastName}"
... />

android:onClick="onLike"

android:onClick="@{() -> viewmodel.onLike()}"

    binding.name = "Your name"
    binding.lastName = "Your last name"

    binding.viewmodel = viewModel

var likes =  0

    val name = "Grace"
    val lastName = "Hopper"
    var likes = 0
        private set // This is to prevent external modification of the variable.

    private val _name = MutableLiveData("Ada")
    private val _lastName = MutableLiveData("Lovelace")
    private val _likes =  MutableLiveData(0)

    val name: LiveData<String> = _name
    val lastName: LiveData<String> = _lastName
    val likes: LiveData<Int> = _likes

    fun onLike() {
        likes++
    }

    /**
     * Returns popularity in buckets: [Popularity.NORMAL],
     * [Popularity.POPULAR] or [Popularity.STAR]
     */
    val popularity: Popularity
        get() {
            return when {
                likes > 9 -> Popularity.STAR
                likes > 4 -> Popularity.POPULAR
                else -> Popularity.NORMAL
            }
        }

   
    // popularity is exposed as LiveData using a Transformation instead of a @Bindable property.
    val popularity: LiveData<Popularity> = Transformations.map(_likes) {
        when {
            it > 9 -> Popularity.STAR
            it > 4 -> Popularity.POPULAR
            else -> Popularity.NORMAL
        }
    }

    fun onLike() {
        _likes.value = (_likes.value ?: 0) + 1
    }

binding.lifecycleOwner = this

    private fun updateLikes() {
        findViewById<TextView>(R.id.likes).text = viewModel.likes.toString()
        findViewById<ProgressBar>(R.id.progressBar).progress =
            (viewModel.likes * 100 / 5).coerceAtMost(100)
...

class PlainOldActivity : AppCompatActivity() {

    // Obtain ViewModel from ViewModelProviders
    private val viewModel by lazy { ViewModelProviders.of(this).get(SimpleViewModel::class.java) }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val binding : PlainActivityBinding =
            DataBindingUtil.setContentView(this, R.layout.plain_activity)

        binding.lifecycleOwner = this

        binding.viewmodel = viewModel
    }
}

        <TextView
                android:id="@+id/likes"
                android:text="@{Integer.toString(viewmodel.likes)}"
...

    @BindingAdapter("android:text")
    public static void setText(TextView view, CharSequence text) {
        // Some checks removed for clarity

        view.setText(text);
    }

    @BindingAdapter("android:background")
    public static void setBackground(View view, Drawable drawable) {
        if (VERSION.SDK_INT >= VERSION_CODES.JELLY_BEAN) {
            view.setBackground(drawable);
        } else {
            view.setBackgroundDrawable(drawable);
        }
    }

    @BindingAdapter("app:hideIfZero")
    fun hideIfZero(view: View, number: Int) {
        view.visibility = if (number == 0) View.GONE else View.VISIBLE
    }

    <ProgressBar
            android:id="@+id/progressBar"
            app:hideIfZero="@{viewmodel.likes}"
...

/**
 *  Sets the value of the progress bar so that 5 likes will fill it up.
 *
 *  Showcases Binding Adapters with multiple attributes. Note that this adapter is called
 *  whenever any of the attribute changes.
 */
@BindingAdapter(value = ["app:progressScaled", "android:max"], requireAll = true)
fun setProgress(progressBar: ProgressBar, likes: Int, max: Int) {
    progressBar.progress = (likes * max / 5).coerceAtMost(max)
}

        <ProgressBar
                android:id="@+id/progressBar"
                app:hideIfZero="@{viewmodel.likes}"
                app:progressScaled="@{viewmodel.likes}"
                android:max="@{100}"
...