Data Binding 界面与代码

<?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="data"
            type="com.example.livedatatest.ViewModelWithLiveData" />
    </data>

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

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(data.likeNumber)}"
            android:textSize="30sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.253" />

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:contentDescription="@string/ImageDescription"
            android:onClick="@{()->data.addLikedNumber(1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.196"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.499"
            app:srcCompat="@drawable/ic_thumb_up_black_24dp" />

        <ImageView
            android:id="@+id/imageView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="4dp"
            android:contentDescription="@string/ImageDescription"
            android:onClick="@{()->data.addLikedNumber(-1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.91"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.499"
            app:srcCompat="@drawable/ic_thumb_down_black_24dp" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

package com.example.livedatatest;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class ViewModelWithLiveData extends ViewModel {
    private MutableLiveData<Integer> LikedNumber;

    public MutableLiveData<Integer> getLikeNumber() {
        if(LikedNumber == null){
            LikedNumber = new MutableLiveData<>();
            LikedNumber.setValue(0);
        }
        return LikedNumber;
    }
    public void addLikedNumber(int n) {
        LikedNumber.setValue(LikedNumber.getValue() + n);
    }
}

package com.example.livedatatest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;

import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.livedatatest.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
    ViewModelWithLiveData viewModelWithLiveData;//管理数据

    ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.activity_main);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);

        viewModelWithLiveData = ViewModelProviders.of(this).get(ViewModelWithLiveData.class);//绑定ViewModel
        binding.setData(viewModelWithLiveData);//设置数据
        binding.setLifecycleOwner(this);//这句是必须的




    }
}