DataBinding的简单使用（java/kotlin）

效果：

一 依赖

implementation ‘com.google.android.material:material:1.0.0’

implementation ‘androidx.lifecycle:lifecycle-extensions:2.2.0’

二 启用

在build.gradle(app)中的testInstrumentationRunner上面添加一句

dataBinding.enabled= true

三 ViewModel

java:

private MutableLiveData<Integer> number;

    public MutableLiveData<Integer> getNumber() {
    
    

        if (number == null) {
    
    

            number = new MutableLiveData<>();

            number.setValue(0);

        }

        return number;

    }

    public void changednumber(Int newnumber) {
    
    

        number.setValue(number.getValue()+newnumber);

    }

kotlin:

private val _number:MutableLiveData<Int> by lazy {
    
     MutableLiveData<Int>(0) }//初始值为0

    var number=_number

    fun changednumber(a:Int){
    
    

        _number.value= _number.value?.plus(a)

    }                                 

四 xml绑定

主要内容：

<data>

        <variable

          name="vm"

          type="com.example.mutablelivedata.MyViewModel" />

</data>

android:text="@{String.valueOf(vm.number)}"

android:onClick="@{()->vm.changednumber(5)}"

android:progress="@{vm.number}"

全部：

<?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
            name="vm"
            type="com.example.kotlinmutablelivedata.MyViewModel" />
    </data>

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

        <TextView
            android:id="@+id/textone"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(vm.number)}"
            android:textSize="30sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+5"
            android:onClick="@{()->vm.changednumber(5)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />

        <SeekBar
            android:id="@+id/seekBar"
            android:progress="@{vm.number}"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginBottom="32dp"
            android:max="15"
            app:layout_constraintBottom_toTopOf="@+id/textone"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />


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

五 活动中启用：

java:

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binding = DataBindingUtil.setContentView(this,R.layout.activity_main);

myViewModel =new ViewModelProvider(this).get(MyViewModel.class);

binding.setVm(myViewModel);

binding.setLifecycleOwner(this);

kotlin:

  val viewModel = ViewModelProvider(this).get(MyViewModel::class.java)

        val binding: ActivityMainBinding =

            DataBindingUtil.setContentView(this, R.layout.activity_main)

        binding.apply {
    
    

            vm = viewModel //设定对象

            lifecycleOwner = this@MainActivity //定义被观察者

        }