Jetpack-- DataBinding結合ViewModel和LiveData使用

簡介

• DataBinding 用來將數據綁定在UI頁面上，實現試圖和數據的雙向綁定，主要是體現數據驅動開發，具體含義是在得到數據後，通過框架在視圖樹中找到與數據綁定的視圖

使用

• 在build.gradle中添加

android {
        ....
    defaultConfig {
        ...
        dataBinding {
            enabled = true
        }
}

• xml中實現雙向綁定

<?xml version="1.0" encoding="utf-8"?>
<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>
        <variable
            // 屬性名，什麼名字都可以，相當於給你的ViewModel起的別名
            name="wjx"
            // 類型
            type="com.wjx.android.jetpackdemo.MyViewModel" />
    </data>


    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">


        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button"
            // 對數據進行操作
            android:onClick="@{()->wjx.setLikedNumber(1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.421" />


        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button"
            android:onClick="@{()->wjx.setLikedNumber(2)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.575" />


        <TextView
            android:id="@+id/textView"
            android:layout_width="86dp"
            android:layout_height="37dp"
            // 數據的顯示和視圖綁定
            android:text="@{String.valueOf(wjx.likedNumber)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.495"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.247" />


    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

• acticity中使用DataBinding

class MainActivity : AppCompatActivity() {
    private lateinit var mViewModel: MyViewModel
    private lateinit var activityMainBinding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // 將視圖綁定
        activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)
        // vm和控制器綁定
        mViewModel = ViewModelProviders.of(this).get(MyViewModel::class.java)
        // 取回數據, this LifeCycleOwner
        activityMainBinding.setWjx(mViewModel)
        // 進行數據觀察
        activityMainBinding.setLifecycleOwner(this)
    }
}