数据直接绑定到UI上，数据改变时UI自动更新 UI上的数据绑定到变量中，当数据(如EditText中的数据)改变时自动更新 DataBinding非常适合用于MVVM模式中充当View和ViewModel的双向通讯的工具，引入DataBinding之后，我们可以少写很多的例如findViewById()之类的代码。

2.引入依赖：

buildFeatures {
    viewBinding true
    dataBinding true
}

3.实体类代码：

/**
 * @author: njb
 * @date: 2022/9/17 21:35
 * @desc:
 */
public class Book {
    public String title;
    public String author;
    public int rating;

    public Book(String title,String author){
        this.title = title;
        this.author= author;
    }

}

4.MainActivity代码：主要是绑定view和设置数据

public class MainActivity extends AppCompatActivity {
    ActivityMainBinding activityMainBinding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initView();
    }

    private void initView() {
        activityMainBinding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        Book book = new Book("AndroidJetPack应用指南学习之DataBinding简单使用","淡淡的香烟");
        book.rating = 5;
        activityMainBinding.setBook(book);
    }
}

5.主界面activity_main代码：

5.1首先是设置数据:

和之前的普通方式不一样，这里布局是以layout开始的，熟悉的小伙伴应该都知道.

<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"
    tools:context=".MainActivity">

    <data>
        <import type="com.example.databindingdemo.utils.BookRatingUtils" />

        <variable
            name="book"
            type="com.example.databindingdemo.bean.Book" />
    </data>

5.2 在布局中设置数据：

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

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="0dp"
        android:layout_height="40dp"
        android:layout_margin="40dp"
        android:background="@color/colorPrimaryDark"
        android:gravity="center"
        android:text="@{book.title}"
        android:textColor="@color/white"
        android:textSize="20sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="0dp"
        android:layout_height="40dp"
        android:layout_margin="40dp"
        android:background="@color/colorPrimaryDark"
        android:gravity="center"
        android:text="@{book.author}"
        android:textColor="@color/white"
        android:textSize="20sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/tv_title" />

    <TextView
        android:id="@+id/tv_rating"
        android:layout_width="0dp"
        android:layout_height="40dp"
        android:layout_margin="40dp"
        android:background="@color/colorPrimaryDark"
        android:gravity="center"
        android:text="@{BookRatingUtils.getRatingString(book.rating)}"
        android:textColor="@color/white"
        android:textSize="20sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/tv_content" />
</androidx.constraintlayout.widget.ConstraintLayout>

5.3 布局完整代码如下：

<?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"
    tools:context=".MainActivity">

    <data>
        <import type="com.example.databindingdemo.utils.BookRatingUtils" />

        <variable
            name="book"
            type="com.example.databindingdemo.bean.Book" />
    </data>

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

        <TextView
            android:id="@+id/tv_title"
            android:layout_width="0dp"
            android:layout_height="40dp"
            android:layout_margin="40dp"
            android:background="@color/colorPrimaryDark"
            android:gravity="center"
            android:text="@{book.title}"
            android:textColor="@color/white"
            android:textSize="20sp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tv_content"
            android:layout_width="0dp"
            android:layout_height="40dp"
            android:layout_margin="40dp"
            android:background="@color/colorPrimaryDark"
            android:gravity="center"
            android:text="@{book.author}"
            android:textColor="@color/white"
            android:textSize="20sp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/tv_title" />

        <TextView
            android:id="@+id/tv_rating"
            android:layout_width="0dp"
            android:layout_height="40dp"
            android:layout_margin="40dp"
            android:background="@color/colorPrimaryDark"
            android:gravity="center"
            android:text="@{BookRatingUtils.getRatingString(book.rating)}"
            android:textColor="@color/white"
            android:textSize="20sp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/tv_content" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

6.评分工具类代码：

package com.example.databindingdemo.utils;

/**
 * @author: njb
 * @date: 2022/9/17 21:52
 * @desc: 评分工具类
 */
public class BookRatingUtils {
    public static String getRatingString(int rat){
        switch (rat){
            case 0:
               return "非常不好看";
            case 1:
                return "不好看";
            case 2:
                return "有一点不好看";
            case 3:
                return "有一点好看";
            case 4:
                return "好看";
            case 5:
                return "非常好看";
        }
        return "";
    }
}

7.实现的效果如下：

8.DataBinding响应事件

8.1 添加一个事件工具类：EventHandlerListener

package com.example.databindingdemo.listener;

import android.content.Context;
import android.view.View;
import android.widget.Toast;

/**
 * @author: njb
 * @date: 2022/9/18 0:02
 * @desc:
 */
public class EventHandlerListener {
    private Context context;
    public EventHandlerListener(Context context){
        this.context = context;
    }

    public void onButtonClicked(View view){
        Toast.makeText(context,"I am clicked!",Toast.LENGTH_SHORT).show();
    }
}

8.2 在布局中添加事件和监听

    <data>
        <import type="com.example.databindingdemo.utils.BookRatingUtils" />

        <variable
            name="book"
            type="com.example.databindingdemo.bean.Book" />

        <variable
            name="EventHandler"
            type="com.example.databindingdemo.listener.EventHandlerListener" />
    </data>
    
    <Button
    android:id="@+id/btn_test"
    android:layout_width="0dp"
    android:layout_height="40dp"
    android:layout_margin="40dp"
    android:background="@color/colorPrimaryDark"
    android:gravity="center"
    android:text="Click me"
    android:textColor="@color/white"
    android:textSize="20sp"
    android:onClick="@{EventHandler.onButtonClicked}"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@id/tv_rating" />

9.添加事件的监听和使用

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    initView();
    initListener();
}

private void initListener() {
    activityMainBinding.setEventHandler(new EventHandlerListener(this));
}

10.事件响应的效果如下：

11.添加自定义的BindingAdapter

/**
 * @author: njb
 * @date: 2022/9/18 0:36
 * @desc: 自定义BindingAdapter
 */
public class BindingAdapterImage {
    @BindingAdapter("image")
    public static void setImage(ImageView image,int imgResource){
        image.setImageResource(imgResource);
    }

    @BindingAdapter("netWorkImage")
    public static void setNetWorkImage(ImageView imageView,String imgUrl){
       if(!TextUtils.isEmpty(imgUrl)){
           Picasso.get().load(imgUrl).placeholder(R.drawable.ic_launcher_background)
                   .error(R.mipmap.ic_launcher).centerCrop().resize(300,300)
                   .into(imageView);
       }else {
           imageView.setBackgroundColor(Color.RED);
       }
    }

    @BindingAdapter("padding")
    public static void setPadding(View view,int oldPadding, int newPadding){
        if(oldPadding != newPadding){
            view.setPadding(newPadding,newPadding,newPadding,newPadding);
        }
    }
}

12.自定义BindAdapter布局如下：

<?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="netWorkImage"
            type="String" />

        <variable
            name="localImage"
            type="int" />

        <variable
            name="imagePadding"
            type="int" />

        <variable
            name="ClickHandler"
            type="com.example.databindingdemo.BindAdapterActivity.ClickHandler" />
    </data>

    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

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

            <ImageView
                android:id="@+id/iv_local"
                android:layout_width="0dp"
                android:layout_height="50dp"
                app:image="@{localImage}"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                tools:ignore="MissingConstraints" />

            <ImageView
                android:id="@+id/iv_netWork"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toBottomOf="@id/iv_local"
                app:netWorkImage="@{netWorkImage}"
                app:padding="@{imagePadding}"
                tools:ignore="MissingConstraints" />

            <Button
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:background="@color/colorPrimary"
                android:onClick="@{ClickHandler.onClick}"
                android:text="change padding"
                android:textAllCaps="false"
                android:textColor="@color/white"
                android:textSize="20sp"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toBottomOf="@id/iv_netWork"
                tools:ignore="MissingConstraints" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.core.widget.NestedScrollView>
</layout>

13.BindAdapterActivity代码：

package com.example.databindingdemo;

import android.os.Bundle;
import android.view.View;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;

import com.example.databindingdemo.databinding.ActivityBindingAdapterBinding;

/**
 * @author: njb
 * @date: 2022/9/18 0:41
 * @desc:
 */
public class BindAdapterActivity extends AppCompatActivity {
    private ActivityBindingAdapterBinding bindingAdapterBinding;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initView();

    }

    private void initView() {
        bindingAdapterBinding = DataBindingUtil.setContentView(this,R.layout.activity_binding_adapter);
        bindingAdapterBinding.setLocalImage(R.mipmap.ic_launcher);
        bindingAdapterBinding.setNetWorkImage("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.zcool.cn%2Fcommunity%2F013b3d5c04dc59a80121ab5d0776b2.jpg%402o.jpg&refer=http%3A%2F%2Fimg.zcool.cn&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1666026424&t=89bb1c43518c696a2000ba442b9be1d6");
        bindingAdapterBinding.setImagePadding(20);

        bindingAdapterBinding.setClickHandler(new ClickHandler());
    }

    public class ClickHandler {
        public void onClick(View view){
            bindingAdapterBinding.setImagePadding(120);
        }
    }
}

14.自定义BindingAdapter效果如下：

改变Padding后的效果如下：

15.使用ViewModel实现双向绑定：

package com.example.databindingdemo.bean;

import android.util.Log;

import androidx.databinding.BaseObservable;
import androidx.databinding.Bindable;

import com.example.databindingdemo.BR;

/**
* @author: njb
* @date: 2022/9/18 16:27
* @desc: 使用ViewModel实现双向绑定
*/
public class TwoWayBindingViewModel extends BaseObservable {
private LoginModel loginModel;

public TwoWayBindingViewModel(){
loginModel = new LoginModel();
loginModel.userName = "JetPack";
}

@Bindable
public String getUserName(){
return loginModel.userName;
}

public void setUserName(String userName){
if(userName != null && !userName.equals(loginModel.userName)){
loginModel.userName = userName;
notifyPropertyChanged(BR.userName);
Log.d("--viewModel--",userName);
}
}
}

16.ViewModel布局和Activity如下：

16.1 ViewModel布局：

<?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">

<data>

<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:layout_width="0dp"
android:layout_height="60dp"
android:background="@color/colorPrimary"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
android:layout_margin="20dp"
android:text="@={viewModel.userName}"
android:textColor="@color/white"
android:textSize="20sp"
android:gravity="center"/>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>

16.2 ViewModelActivity代码如下：

package com.example.databindingdemo;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;

import com.example.databindingdemo.bean.TwoWayBindingViewModel;
import com.example.databindingdemo.bean.TwoWayBindingViewModelField;
import com.example.databindingdemo.databinding.ActivityTwoWayBindingBinding;

/**
* @author: njb
* @date: 2022/9/18 16:30
* @desc:
*/
public class TwoWayBindingActivity extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
initView();
}

private void initView() {
ActivityTwoWayBindingBinding twoWayBindingBinding = DataBindingUtil.setContentView(this,R.layout.activity_two_way_binding);
twoWayBindingBinding.setViewModel(new TwoWayBindingViewModel());

//twoWayBindingBinding.setViewModel(new TwoWayBindingViewModelField());
}
}

17.使用ObservableField优化双向绑定：

17.1 TwoWayBindingViewModelField类：

package com.example.databindingdemo.bean;

import android.util.Log;

import androidx.databinding.BaseObservable;
import androidx.databinding.ObservableField;

/**
* @author: njb
* @date: 2022/9/18 16:42
* @desc: 使用ObservableField优化双向绑定
*/
public class TwoWayBindingViewModelField extends BaseObservable {
private ObservableField<LoginModel> loginModelObservableField;

public TwoWayBindingViewModelField() {
LoginModel loginModel = new LoginModel();
loginModel.userName = "Jack";
loginModelObservableField = new ObservableField<>();
loginModelObservableField.set(loginModel);
}

public void setUserName(String userName) {
loginModelObservableField.get().userName = userName;
Log.d("--fieldViewModel--", userName);
}

public String getUserName() {
return loginModelObservableField.get().userName;
}
}

17.2 布局中使用方式如下：

17.3 Activity中使用代码：

17.4 日志打印：

可以看到两种方式基本上差不多，使用ObservableField方式时通过ObservableField将LoginModel对象包装起来，并为对象写好Getter和Setter方法，在布局中依然通过@={}的方式完成双向绑定，运行程序发现getUserName方法在程序启动时被自动调用,当用户修改EditText中的内容时setUserName被自动调用,对于Getter方法也无需添加@Bindable，使用方便了许多.

18.双向绑定的运行效果图如下：

19.RecyclerView的双向绑定机制:

19.1 RecyclerViewAdapter:

package com.example.databindingdemo.adapter;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.databinding.DataBindingUtil;
import androidx.recyclerview.widget.RecyclerView;

import com.example.databindingdemo.R;
import com.example.databindingdemo.bean.Book;
import com.example.databindingdemo.databinding.LayoutItemBinding;

import java.util.List;

/**
 * @author: njb
 * @date: 2022/9/18 17:16
 * @desc:
 */
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> {
    private List<Book> bookList;

    public RecyclerViewAdapter(List<Book> books){
        this.bookList = books;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutItemBinding layoutItemBinding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()),R.layout.layout_item,parent,false);

        return new MyViewHolder(layoutItemBinding);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
       Book book = bookList.get(position);
       holder.layoutItemBinding.setBook(book);
    }

    @Override
    public int getItemCount() {
        return bookList.size();
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {
        LayoutItemBinding layoutItemBinding;

        public MyViewHolder(LayoutItemBinding itemView) {
            super(itemView.getRoot());
            layoutItemBinding = itemView;
        }
    }
}

19.2 RecyclerViewBindingAdapter代码：

package com.example.databindingdemo.adapter;

import android.graphics.Color;
import android.text.TextUtils;
import android.widget.ImageView;

import androidx.databinding.BindingAdapter;

import com.example.databindingdemo.R;
import com.squareup.picasso.Picasso;

/**
 * @author: njb
 * @date: 2022/9/18 17:07
 * @desc:
 */
public class RecyclerViewBindingAdapter {
    @BindingAdapter("itemImage")
    public static void setNetWorkImage(ImageView imageView, String imgUrl){
        if(!TextUtils.isEmpty(imgUrl)){
            Picasso.get().load(imgUrl).placeholder(R.drawable.ic_launcher_background)
                    .error(R.mipmap.ic_launcher).centerCrop().resize(300,300)
                    .into(imageView);
        }else {
            imageView.setBackgroundColor(Color.RED);
        }
    }
}

19.3 RecyclerViewViewModel代码：

/**
 * @author: njb
 * @date: 2022/9/18 17:12
 * @desc:
 */
public class RecyclerViewViewModel {
    public List<Book> getBooks(){
        List<Book> books = new ArrayList<>();
        for(int i=0;i<100;i++){
            Book book = new Book(Constants.title,Constants.content);
            book.img = Constants.imgUrl;
            books.add(book);
        }
        return  books;
    }
}

19.4 layout_item布局代码：

<?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">

    <data>

        <variable
            name="book"
            type="com.example.databindingdemo.bean.Book" />

        <variable
            name="EventHandler"
            type="com.example.databindingdemo.listener.EventHandlerListener" />
    </data>

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

        <ImageView
            android:id="@+id/iv_local"
            android:layout_width="140dp"
            android:layout_height="140dp"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:gravity="center"
            app:itemImage="@{book.img}"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tv_title"
            android:layout_width="0dp"
            android:layout_height="40dp"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:layout_marginEnd="20dp"
            android:background="@color/colorPrimaryDark"
            android:gravity="center"
            android:text="@{book.title}"
            android:textColor="@color/white"
            android:textSize="20sp"
            app:layout_constraintLeft_toRightOf="@+id/iv_local"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tv_content"
            android:layout_width="0dp"
            android:layout_height="40dp"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:layout_marginEnd="20dp"
            android:background="@color/colorPrimaryDark"
            android:gravity="center"
            android:text="@{book.author}"
            android:textColor="@color/white"
            android:textSize="20sp"
            app:layout_constraintLeft_toRightOf="@+id/iv_local"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/tv_title" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

19.5 RecyclerViewActivity代码：

package com.example.databindingdemo.activity;

import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.recyclerview.widget.LinearLayoutManager;

import com.example.databindingdemo.R;
import com.example.databindingdemo.adapter.RecyclerViewAdapter;
import com.example.databindingdemo.databinding.ActivityRecyclerBindingAdapterBinding;
import com.example.databindingdemo.viewmodel.RecyclerViewViewModel;

/**
 * @author: njb
 * @date: 2022/9/18 17:26
 * @desc:
 */
public class RecyclerViewActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initView();
    }

    private void initView() {
        ActivityRecyclerBindingAdapterBinding recyclerBindingAdapterBinding = DataBindingUtil.setContentView(this, R.layout.activity_recycler_binding_adapter);
        recyclerBindingAdapterBinding.recyclerView.setHasFixedSize(true);
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(new RecyclerViewViewModel().getBooks());
        recyclerBindingAdapterBinding.recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerBindingAdapterBinding.recyclerView.setAdapter(adapter);
    }
}

19.6 RecyclerViewActivity布局代码：

<?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">

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

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

20.RecyclerView实现双向绑定的效果如下：

21.项目源码如下：

DataBindingDemo: DataBinding的简单使用

原文链接：https://blog.csdn.net/u012556114/article/details/126912409