Jetpack ViewBinding
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
<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">
<TextView
android:id="@+id/tv_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tv_age"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<ImageView
android:id="@+id/iv_avatar"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<Button
android: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? = null
private val viewBinding
get() = _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? = null
private val viewBinding
get() = _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
不使用merge标签
- 一定要给
XML布局
title_bar.xml
<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">
<TextView
android:id="@+id/back"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:text="返回" />
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="标题位置" />
<TextView
android: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
<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">
<include
android:id="@+id/titleBar"
layout="@layout/titlebar" />
LinearLayout>
在include标签中使用
public class IncludeActivity extends AppCompatActivity {
private Context context;
@Override
protected 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() {
@Override
public void onClick(View v) {
Toast.makeText(context, "返回", Toast.LENGTH_SHORT).show();
}
});
binding.titleBar.confirm.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(context, "确定", Toast.LENGTH_SHORT).show();
}
});
}
}
使用merge标签
- 需要使用
bind()方法绑定根视图。 - 不能给
布局：detail_layout.xml
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<ImageView
android:id="@+id/ivDetail"
android:layout_width="100dp"
android:layout_height="100dp"
android:scaleType="fitXY" />
merge>
Activity的XML布局
<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;
@Override
protected 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: VB
protected val mViewBinding get() = _viewBinding
override 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: VB
protected val mViewBinding get() = _viewBinding
override 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: VB
protected val mViewBinding get() = _viewBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mContext = this
val type = javaClass.genericSuperclass
if (type is ParameterizedType) {
val clz = type.actualTypeArguments[0] as Class<*>
val method = clz.getMethod("inflate", LayoutInflater::class.java)
_viewBinding = method.invoke(null, layoutInflater) as VB
setContentView(_viewBinding.root)
}
}
}
abstract class BindingFragment<VB : ViewBinding> : BaseFragment() {
private var _viewBinding: VB? = null
protected val mViewBinding get() = _viewBinding!!
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
): View {
val type = javaClass.genericSuperclass
if (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 ViewBinding
inline 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? = null
override 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? = null
override 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 ViewBinding
inline 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? = null
override fun getValue(thisRef: Fragment, property: KProperty<*>): VB {
viewBinding?.let { return it }
val lifecycle = thisRef.viewLifecycleOwner.lifecycle
viewBinding = 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? = null
private val bindMethod = clazz.getMethod("bind", View::class.java)
override fun getValue(thisRef: Fragment, property: KProperty<*>): VB {
viewBinding?.let { return it }
val lifecycle = thisRef.viewLifecycleOwner.lifecycle
viewBinding = bindMethod.invoke(null, thisRef.requireView()) as VB
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!!
}
}
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()
}
}
}