Android开发Jetpack-Databinding基本使用

官方文档地址：https://developer.android.com/topic/libraries/data-binding

人类自从有Android系统以来，我们绑定数据从findViewById开始，需要强转控件类型，随着SDK的升级，不再需要强转类型。顺带还有黄油刀，就是为了简化我们的开发。

我们可以不再使用findViewById去找控件，然后再设置数据了。如果数据更新了,还得重新设置。接下来我们就了解一下Databinding吧。

所以接下来我们要通过Databinding实现一般页面的数据绑定，列表的数据绑定，图片的数据绑定等常见的场景。

让你的项目支持Databinding

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

基本使用

先来一个布局，我们要显示用户的信息，包括姓名，年龄和性别

创建bean类，用于封装用户数据

package com.sunofbeaches.databindingdemo.domain

data class User(var name: String, var age: Int, var gender: Gender)

enum class Gender {
    FEMALE, MALE
}

布局代码

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>

        <variable
            name="user"
            type="com.sunofbeaches.databindingdemo.domain.User" />
    </data>

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

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.10259918" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.2" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.3" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.3" />

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/text_name"
            app:layout_constraintBottom_toTopOf="@+id/guideline"
            app:layout_constraintEnd_toStartOf="@+id/guideline4"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/text_age"
            app:layout_constraintBottom_toTopOf="@+id/guideline2"
            app:layout_constraintEnd_toStartOf="@+id/guideline4"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline" />

        <TextView
            android:id="@+id/textView3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/text_gender"
            app:layout_constraintBottom_toTopOf="@+id/guideline3"
            app:layout_constraintEnd_toStartOf="@+id/guideline4"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline2" />

        <TextView
            android:id="@+id/textView4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{user.name}"
            app:layout_constraintBottom_toTopOf="@+id/guideline"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="@+id/guideline4"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{user.gender.toString()}"
            app:layout_constraintBottom_toTopOf="@+id/guideline3"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="@+id/guideline4"
            app:layout_constraintTop_toTopOf="@+id/guideline2" />

        <TextView
            android:id="@+id/textView7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(user.age)}"
            app:layout_constraintBottom_toTopOf="@+id/guideline2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="@+id/guideline4"
            app:layout_constraintTop_toTopOf="@+id/guideline" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

MainActivity.kt的代码

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //把布局交给DataBindingUtil
        val activityMainBinding: ActivityMainBinding =
            DataBindingUtil.setContentView(this, R.layout.activity_main)
        //设置数据
        activityMainBinding.user = User("TrillGates", 30, Gender.MALE)
    }
}

运行结果

由此，我们就完成了数据的绑定，我们没有给控件起id，里面的id是自动生成的，我们不用也行。这是不是跟vue.js里一样呀，绑定数据就可以了，非常简单。

说明

• 这里面我们布局最外层使用Layout标签进行包裹
• layout你可以手动写，或者按alt+回车提示你自动改

• data标签

<data>
    <variable
              name="user"
              type="com.sunofbeaches.databindingdemo.domain.User" />
</data>

这里面我们用于置顶bean类，也可以这样写：

<data>
    <import type="com.sunofbeaches.databindingdemo.domain.User" />
    <variable
              name="user"
              type="User" />
</data>

• ActivityMainBinding是自动生成的类，大家可以看看以下代码，对应着以上的布局代码

// Generated by data binding compiler. Do not edit!
package com.sunofbeaches.databindingdemo.databinding;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.constraintlayout.widget.Guideline;
import androidx.databinding.Bindable;
import androidx.databinding.DataBindingUtil;
import androidx.databinding.ViewDataBinding;
import com.sunofbeaches.databindingdemo.R;
import com.sunofbeaches.databindingdemo.domain.User;
import java.lang.Deprecated;
import java.lang.Object;

public abstract class ActivityMainBinding extends ViewDataBinding {
  @NonNull
  public final Guideline guideline;

  @NonNull
  public final Guideline guideline2;

  @NonNull
  public final Guideline guideline3;

  @NonNull
  public final Guideline guideline4;

  @NonNull
  public final TextView textView;

  @NonNull
  public final TextView textView2;

  @NonNull
  public final TextView textView3;

  @NonNull
  public final TextView textView4;

  @NonNull
  public final TextView textView6;

  @NonNull
  public final TextView textView7;

  @Bindable
  protected User mUser;

  protected ActivityMainBinding(Object _bindingComponent, View _root, int _localFieldCount,
      Guideline guideline, Guideline guideline2, Guideline guideline3, Guideline guideline4,
      TextView textView, TextView textView2, TextView textView3, TextView textView4,
      TextView textView6, TextView textView7) {
    super(_bindingComponent, _root, _localFieldCount);
    this.guideline = guideline;
    this.guideline2 = guideline2;
    this.guideline3 = guideline3;
    this.guideline4 = guideline4;
    this.textView = textView;
    this.textView2 = textView2;
    this.textView3 = textView3;
    this.textView4 = textView4;
    this.textView6 = textView6;
    this.textView7 = textView7;
  }

  public abstract void setUser(@Nullable User user);

  @Nullable
  public User getUser() {
    return mUser;
  }

  @NonNull
  public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,
      @Nullable ViewGroup root, boolean attachToRoot) {
    return inflate(inflater, root, attachToRoot, DataBindingUtil.getDefaultComponent());
  }

  /**
   * This method receives DataBindingComponent instance as type Object instead of
   * type DataBindingComponent to avoid causing too many compilation errors if
   * compilation fails for another reason.
   * https://issuetracker.google.com/issues/116541301
   * @Deprecated Use DataBindingUtil.inflate(inflater, R.layout.activity_main, root, attachToRoot, component)
   */
  @NonNull
  @Deprecated
  public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,
      @Nullable ViewGroup root, boolean attachToRoot, @Nullable Object component) {
    return ViewDataBinding.<ActivityMainBinding>inflateInternal(inflater, R.layout.activity_main, root, attachToRoot, component);
  }

  @NonNull
  public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater) {
    return inflate(inflater, DataBindingUtil.getDefaultComponent());
  }

  /**
   * This method receives DataBindingComponent instance as type Object instead of
   * type DataBindingComponent to avoid causing too many compilation errors if
   * compilation fails for another reason.
   * https://issuetracker.google.com/issues/116541301
   * @Deprecated Use DataBindingUtil.inflate(inflater, R.layout.activity_main, null, false, component)
   */
  @NonNull
  @Deprecated
  public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,
      @Nullable Object component) {
    return ViewDataBinding.<ActivityMainBinding>inflateInternal(inflater, R.layout.activity_main, null, false, component);
  }

  public static ActivityMainBinding bind(@NonNull View view) {
    return bind(view, DataBindingUtil.getDefaultComponent());
  }

  /**
   * This method receives DataBindingComponent instance as type Object instead of
   * type DataBindingComponent to avoid causing too many compilation errors if
   * compilation fails for another reason.
   * https://issuetracker.google.com/issues/116541301
   * @Deprecated Use DataBindingUtil.bind(view, component)
   */
  @Deprecated
  public static ActivityMainBinding bind(@NonNull View view, @Nullable Object component) {
    return (ActivityMainBinding)bind(component, view, R.layout.activity_main);
  }
}