文章目录

Jetpack ViewBinding
- 概述
- ViewBinding优点
- 配置ViewBinding
- 使用
- - 在Activity中使用
  - 在Fragment中使用
  - 在RecyclerView adapter中使用
  - 在include标签中使用
  - - 不使用merge标签
    - 使用merge标签
- 封装使用
- - 基类封装，不使用反射
  - 基类封装，使用反射
  - 委托实现
- 源码分析
- 代码下载

Jetpack ViewBinding

概述

官网文档

通过视图绑定功能，您可以更轻松地编写可与视图交互的代码。在模块中启用视图绑定之后，系统会为该模块中的每个 XML 布局文件生成一个绑定类。绑定类的实例包含对在相应布局中具有 ID 的所有视图的直接引用。

ViewBinding优点

ViewBinding优点

Null 安全：由于视图绑定会创建对视图的直接引用，因此不存在因视图 ID 无效而引发 Null 指针异常的风险。
类型安全：每个绑定类中的字段均具有与它们在 XML 文件中引用的视图相匹配的类型。因此不存强制转换导致的异常风险。

与findViewById区别

findViewById编写过于冗余。
类型仍然不安全。

与ButterKnife区别

官宣不维护，推荐使用ViewBinding。
类型仍然不安全。
对组件化项目不友好。

与Kotlin Android Extensions

JetBrains废弃该插件。
类型仍然不安全。
性能偏低。

配置ViewBinding

Android Studio3.6以上

android {viewBinding {enabled = true}
}

Android Studio4.0以上

android {buildFeatures {viewBinding = true}
}

如果需要忽略某个布局文件，需要添加tools:viewBindingIgnore="true"属性到布局中

<LinearLayout...tools:viewBindingIgnore="true" >...
</LinearLayout>

使用

当开启ViewBinding后，系统会为该模块中每个XML布局文件生成一个绑定类（转换为驼峰命名并在末尾添加Binding），每个绑定类均包含根视图已交具有id的所有视图的引用。

例如：布局文件名为activity_main.xml，生成绑定类为ActivityMainBinding

在Activity中使用

使用流程

开启视图绑定功能后，系统会为该模块中的XML布局生成一个绑定类，每个绑定类都包含根布局和具有ID布局的引用。
调用绑定类的inflate()方法获取绑定类对象。
调用绑定类对象的getRoot()方法获取根布局传递到setContentView()。

XML布局

activity_view_binding_simple.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center_horizontal"android:orientation="vertical"><TextViewandroid:id="@+id/tv_name"android:layout_width="wrap_content"android:layout_height="wrap_content" /><TextViewandroid:id="@+id/tv_age"android:layout_width="wrap_content"android:layout_height="wrap_content" /><ImageViewandroid:id="@+id/iv_avatar"android:layout_width="wrap_content"android:layout_height="wrap_content" /><Buttonandroid:id="@+id/btn"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="确定" />
</LinearLayout>

Activity类

class ViewBindingSimpleActivity : BaseActivity() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)val viewBinding = ActivityViewBindingSimpleBinding.inflate(layoutInflater)setContentView(viewBinding.root)viewBinding.tvName.text = "hello world"viewBinding.tvAge.text = 18.toString()viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)viewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()}}
}

在Fragment中使用

方式一

调用绑定类的inflate()方法，获取绑定类对象。
再调用getRoot()方法获取根布局。
在onCreateView()方法返回根布局，使其成为屏幕上的活动视图。
由于Fragment的存在时间比视图长。因此需要在Fragment的onDestroyView()方法中清除对绑定类对象的所有引用。

class MyFragment : BaseFragment() {private var _viewBinding: FragmentMyBinding? = nullprivate val viewBindingget() = _viewBinding!!override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {_viewBinding = FragmentMyBinding.inflate(inflater, container, false)return viewBinding.root}override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)viewBinding.tvName.text = "hello world"viewBinding.tvAge.text = 18.toString()viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)viewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()}}override fun onDestroyView() {super.onDestroyView()_viewBinding = null}
}

方式二

class MyFragment : BaseFragment() {private var _viewBinding: FragmentMyBinding? = nullprivate val viewBindingget() = _viewBinding!!override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {return inflater.inflate(R.layout.fragment_my, container, false)}override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)_viewBinding = FragmentMyBinding.bind(view)viewBinding.tvName.text = "hello world"viewBinding.tvAge.text = 18.toString()viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)viewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()}}override fun onDestroyView() {super.onDestroyView()_viewBinding = null}
}

在RecyclerView adapter中使用

class MyAdapter(context: Context, private val data: ArrayList<String>) :RecyclerView.Adapter<MyAdapter.ViewHolder>() {val layoutInflater: LayoutInflater = LayoutInflater.from(context)class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {val text: TextView = itemView.findViewById(R.id.text)}override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {val viewBinding = ItemTextBinding.inflate(layoutInflater, parent, false)return ViewHolder(viewBinding.root)}override fun onBindViewHolder(holder: ViewHolder, position: Int) {holder.text.text = data[position]}override fun getItemCount(): Int {return data.size}
}

在include标签中使用

ViewBinding可以与<include>标签一起使用

不使用merge标签

一定要给<include>标签定义id，使用该id访问布局中的控件。

XML布局

title_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="wrap_content"android:background="#2196F3"android:minHeight="50dp"android:padding="10dp"><TextViewandroid:id="@+id/back"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerVertical="true"android:text="返回" /><TextViewandroid:id="@+id/title"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerInParent="true"android:text="标题位置" /><TextViewandroid:id="@+id/confirm"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentRight="true"android:layout_centerVertical="true"android:text="确定" /></RelativeLayout>

Activity的XML布局

activity_vbinclude.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".IncludeActivity"><includeandroid:id="@+id/titleBar"layout="@layout/titlebar" /></LinearLayout>

在include标签中使用

public class IncludeActivity extends AppCompatActivity {private Context context;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);context = this;ActivityIncludeBinding binding = ActivityIncludeBinding.inflate(getLayoutInflater());setContentView(binding.getRoot());binding.titleBar.title.setText("这是一个标题");binding.titleBar.back.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Toast.makeText(context, "返回", Toast.LENGTH_SHORT).show();}});binding.titleBar.confirm.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Toast.makeText(context, "确定", Toast.LENGTH_SHORT).show();}});}
}

使用merge标签

<merge>标签有利于减少布局层次。
需要使用bind()方法绑定根视图。
不能给<include>标签设置id。

布局：detail_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"><ImageViewandroid:id="@+id/ivDetail"android:layout_width="100dp"android:layout_height="100dp"android:scaleType="fitXY" />
</merge>

Activity的XML布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"android:orientation="vertical"tools:context=".IncludeActivity"><include layout="@layout/detail_layout" /></LinearLayout>

在include标签中使用

package com.example.viewbindingdemo;import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;import androidx.appcompat.app.AppCompatActivity;import com.example.viewbindingdemo.databinding.ActivityIncludeBinding;
import com.example.viewbindingdemo.databinding.DetailLayoutBinding;public class IncludeActivity extends AppCompatActivity {private Context context;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);context = this;ActivityIncludeBinding binding = ActivityIncludeBinding.inflate(getLayoutInflater());setContentView(binding.getRoot());DetailLayoutBinding detailBinding = DetailLayoutBinding.bind(binding.getRoot());detailBinding.ivDetail.setImageResource(R.mipmap.ic_launcher);}
}

封装使用

基类封装，不使用反射

基类封装

abstract class BindingActivity<VB : ViewBinding> : BaseActivity() {private lateinit var _viewBinding: VBprotected val mViewBinding get() = _viewBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)_viewBinding = getViewBinding()setContentView(_viewBinding.root)}abstract fun getViewBinding(): VB
}abstract class BindingFragment<VB : ViewBinding> : BaseFragment() {private lateinit var _viewBinding: VBprotected val mViewBinding get() = _viewBindingoverride fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View? {_viewBinding = getViewBinding(inflater, container)return _viewBinding.root}abstract fun getViewBinding(inflater: LayoutInflater, container: ViewGroup?): VB
}

使用

class OneActivity : BindingActivity<ActivityOneBinding>() { override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)mViewBinding.tvName.text = "小白"mViewBinding.tvAge.text = 18.toString()mViewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()}}override fun getViewBinding(): ActivityOneBinding {return ActivityOneBinding.inflate(layoutInflater)}
}class OneFragment : BindingFragment<FragmentOneBinding>() {override fun getViewBinding(inflater: LayoutInflater,container: ViewGroup?): FragmentOneBinding {return FragmentOneBinding.inflate(inflater, container, false)}override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)mViewBinding.tvName.text = "小白"mViewBinding.tvAge.text = 18.toString()mViewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()}}
}

基类封装，使用反射

基类封装

abstract class BindingActivity<VB : ViewBinding> : BaseActivity() {private lateinit var _viewBinding: VBprotected val mViewBinding get() = _viewBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)mContext = thisval type = javaClass.genericSuperclassif (type is ParameterizedType) {val clz = type.actualTypeArguments[0] as Class<*>val method = clz.getMethod("inflate", LayoutInflater::class.java)_viewBinding = method.invoke(null, layoutInflater) as VBsetContentView(_viewBinding.root)}}
}abstract class BindingFragment<VB : ViewBinding> : BaseFragment() {private var _viewBinding: VB? = nullprotected val mViewBinding get() = _viewBinding!!override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {val type = javaClass.genericSuperclassif (type is ParameterizedType) {val clz = type.actualTypeArguments[0] as Class<*>val method = clz.getMethod("inflate", LayoutInflater::class.java, ViewGroup::class.java, Boolean::class.java)_viewBinding = method.invoke(null, inflater, container, false) as VB}return mViewBinding.root}override fun onDestroyView() {super.onDestroyView()_viewBinding = null}
}

使用

class TwoActivity : BindingActivity<ActivityTwoBinding>() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)mViewBinding.tvName.text = "小白"mViewBinding.tvAge.text = 28.toString()mViewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello2", Toast.LENGTH_SHORT).show()}}
}class TwoFragment : BindingFragment<FragmentTwoBinding>() {override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)mViewBinding.tvName.text = "小白"mViewBinding.tvAge.text = 28.toString()mViewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello2", Toast.LENGTH_SHORT).show()}}
}

委托实现

封装

//Activity ViewBindinginline fun <reified VB : ViewBinding> ComponentActivity.viewBindings(noinline factory: (LayoutInflater) -> VB,setContentView: Boolean = true
) = ActivityViewBindingDelegate1(factory, setContentView)inline fun <reified VB : ViewBinding> ComponentActivity.viewBindings(setContentView: Boolean = true) =ActivityViewBindingDelegate2(VB::class.java, setContentView)class ActivityViewBindingDelegate1<VB : ViewBinding>(private val factory: (LayoutInflater) -> VB,private val setContentView: Boolean,
) : ReadOnlyProperty<ComponentActivity, VB> {private var viewBinding: VB? = nulloverride fun getValue(thisRef: ComponentActivity, property: KProperty<*>): VB {viewBinding?.let { return it }viewBinding = factory(thisRef.layoutInflater).also { viewBinding ->if (setContentView) thisRef.setContentView(viewBinding.root)}return viewBinding!!}
}class ActivityViewBindingDelegate2<VB : ViewBinding>(private val clazz: Class<VB>,private val setContentView: Boolean,
) : ReadOnlyProperty<ComponentActivity, VB> {private var viewBinding: VB? = nulloverride fun getValue(thisRef: ComponentActivity, property: KProperty<*>): VB {viewBinding?.let { return it }val inflateMethod = clazz.getMethod("inflate", LayoutInflater::class.java)viewBinding =(inflateMethod.invoke(null, thisRef.layoutInflater) as VB).also { viewBinding ->if (setContentView) thisRef.setContentView(viewBinding.root)}return viewBinding!!}
}

//Fragment ViewBindinginline fun <reified VB : ViewBinding> Fragment.viewBindings(noinline factory: (View) -> VB) =FragmentViewBindingDelegate1(factory)inline fun <reified VB : ViewBinding> Fragment.viewBindings() =FragmentViewBindingDelegate2(VB::class.java)class FragmentViewBindingDelegate1<VB : ViewBinding>(private val factory: (View) -> VB,
) : ReadOnlyProperty<Fragment, VB> {private var viewBinding: VB? = nulloverride fun getValue(thisRef: Fragment, property: KProperty<*>): VB {viewBinding?.let { return it }val lifecycle = thisRef.viewLifecycleOwner.lifecycleviewBinding = factory(thisRef.requireView())if (lifecycle.currentState == Lifecycle.State.DESTROYED) {Log.w("TAG","Access to viewBinding after Lifecycle is destroyed or hasn't created yet. The instance of viewBinding will be not cached.")} else {thisRef.viewLifecycleOwnerLiveData.observe(thisRef) { viewLifecycleOwner ->viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {override fun onDestroy(owner: LifecycleOwner) {viewBinding = null}})}}return viewBinding!!}
}class FragmentViewBindingDelegate2<VB : ViewBinding>(clazz: Class<VB>,
) : ReadOnlyProperty<Fragment, VB> {private var viewBinding: VB? = nullprivate val bindMethod = clazz.getMethod("bind", View::class.java)override fun getValue(thisRef: Fragment, property: KProperty<*>): VB {viewBinding?.let { return it }val lifecycle = thisRef.viewLifecycleOwner.lifecycleviewBinding = bindMethod.invoke(null, thisRef.requireView()) as VBif (lifecycle.currentState == Lifecycle.State.DESTROYED) {Log.w("TAG","Access to viewBinding after Lifecycle is destroyed or hasn't created yet. The instance of viewBinding will be not cached.")} else {thisRef.viewLifecycleOwnerLiveData.observe(thisRef) { viewLifecycleOwner ->viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {override fun onDestroy(owner: LifecycleOwner) {viewBinding = null}})}}return viewBinding!!}
}

使用

class ThreeActivity : BaseActivity() {//方式一private val viewBinding: ActivityThreeBinding by viewBindings(ActivityThreeBinding::inflate)//方式二//    private val viewBinding: ActivityThreeBinding by viewBindings()override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)viewBinding.tvName.text = "小白"viewBinding.tvAge.text = 38.toString()viewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello3", Toast.LENGTH_SHORT).show()}}
}class ThreeFragment : BaseFragment(R.layout.fragment_three) {//方式一
//    private val viewBinding: FragmentThreeBinding by viewBindings(FragmentThreeBinding::bind)//方式二private val viewBinding: FragmentThreeBinding by viewBindings()override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)viewBinding.tvName.text = "小白33"viewBinding.tvAge.text = 338.toString()viewBinding.btn.setOnClickListener {Toast.makeText(mContext, "hello33", Toast.LENGTH_SHORT).show()}}
}

源码分析

代码下载