View Binding 是Google推出的视图绑定组件,启动View Binding之后,系统会为我们添加每个xml布局文件都自动生成一个对应的绑定类。绑定类的实例包含对在相应布局中具有ID的所有的view的直接引用。下面文章会介绍使用,以及分析原理。
注意:View Binding只能在Android Studio3.6 Canary 11及更高版本中可用
一:依赖
在app的build.gradle文件里添加如下:
android {
...
buildFeatures {
viewBinding true
}
}
二:根据布局文件自动生成XxxBinding类
创建一个布局,并且重新编译,比如布局文件为activity_main.xml。那么系统会自动在app->build->generated->data_binding_base_class_source_out->debug->out->包名->databinding 下自动创建一个ActivityMainBinding.java文件。
ActivityMainBinding.java的文件命名由来是activity_main 改成头峰的形式命名。代码如下:
<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=".ui.activity.MainActivity">
<TextView
android:id="@+id/tv_name"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:gravity="center"
android:text="Hello World!"
android:textColor="@color/colorPrimary"
android:textSize="15sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/btn_commit"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:text="完成"
android:textSize="15sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_name" />
<FrameLayout
android:id="@+id/layout_content"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toBottomOf="@+id/btn_commit" />
</androidx.constraintlayout.widget.ConstraintLayout>
布局里最外层是ConstraintLayout,包含的View有 TextView,Button,FramLayout。来看看对应的自动生成的ActivityMainBinding.java类的代码
public final class ActivityMainBinding implements ViewBinding {
@NonNull
private final ConstraintLayout rootView;
@NonNull
public final Button btnCommit;
@NonNull
public final FrameLayout layoutContent;
@NonNull
public final TextView tvName;
private ActivityMainBinding(@NonNull ConstraintLayout rootView, @NonNull Button btnCommit,
@NonNull FrameLayout layoutContent, @NonNull TextView tvName) {
this.rootView = rootView;
this.btnCommit = btnCommit;
this.layoutContent = layoutContent;
this.tvName = tvName;
}
@Override
@NonNull
public ConstraintLayout getRoot() {
return rootView;
}
@NonNull
public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater) {
return inflate(inflater, null, false);
}
@NonNull
public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,
@Nullable ViewGroup parent, boolean attachToParent) {
View root = inflater.inflate(R.layout.activity_main, parent, false);
if (attachToParent) {
parent.addView(root);
}
return bind(root);
}
@NonNull
public static ActivityMainBinding bind(@NonNull View rootView) {
// The body of this method is generated in a way you would not otherwise write.
// This is done to optimize the compiled bytecode for size and performance.
String missingId;
missingId: {
Button btnCommit = rootView.findViewById(R.id.btn_commit);
if (btnCommit == null) {
missingId = "btnCommit";
break missingId;
}
FrameLayout layoutContent = rootView.findViewById(R.id.layout_content);
if (layoutContent == null) {
missingId = "layoutContent";
break missingId;
}
TextView tvName = rootView.findViewById(R.id.tv_name);
if (tvName == null) {
missingId = "tvName";
break missingId;
}
return new ActivityMainBinding((ConstraintLayout) rootView, btnCommit, layoutContent, tvName);
}
throw new NullPointerException("Missing required view with ID: ".concat(missingId));
}
}
- ActivityMainBinding里4个成员变量对应布局文件activity_main.xml里的4个View
- ActivityMainBinding里构造器是传入4个控件
- ActivityMainBinding的getRoot()方法返回的最外层控件
- ActivityMainBinding的inflate方法是 View root = inflater.inflate(R.layout.activity_main, parent, false);根据activity_main布局创建出view,并执行bind方法
- ActivityMainBinding的bind方法是fingViewById绑定控件,并生成ActivityMainBinding实例
三:在Activity中使用XXXBinding
上面我们已经自动生成了ActivitMainBinding类,看我们如何在MainActivity里使用它,如下:
class MainActivity : AppCompatActivity() ,View.OnClickListener{
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.tvName.text = "View Binding Text"
binding.btnCommit.text = "View Binding Btn"
binding.btnCommit.setOnClickListener(this)
supportFragmentManager.beginTransaction().replace(R.id.layout_content,LoginFragment()).commitAllowingStateLoss()
}
override fun onClick(v: View?) {
when(v){
binding.btnCommit-> Toast.makeText(this,"click btn",Toast.LENGTH_SHORT).show()
}
}
}
- binding = ActivityMainBinding.inflate(layoutInflater) 根据上面我们分析的ActivityMainBinding类的源码,可以知道inflate方法根据activity_main.xml去创建View,并把生成的View,通过构造器传入ActivityMainBinding,最终去创建出ActivityMainBinding实例
- setContentView(binding.root) 把binding的最外层布局作为contentView
- binding.tvName,binding.btnCommit 接着就可以通过binding去使用里面的view了
四:在Fragment中使用
新建一个fragment_login.xml布局
// fragment_login.xml的布局如下
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/btn_login"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:gravity="center"
android:text="登录"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
重新编译会自动帮我们生成FragmentMainBinding类
// 对应的自动生成的FragmentLoginBinding类
public final class FragmentLoginBinding implements ViewBinding {
@NonNull
private final ConstraintLayout rootView;
@NonNull
public final Button btnLogin;
private FragmentLoginBinding(@NonNull ConstraintLayout rootView, @NonNull Button btnLogin) {
this.rootView = rootView;
this.btnLogin = btnLogin;
}
@Override
@NonNull
public ConstraintLayout getRoot() {
return rootView;
}
@NonNull
public static FragmentLoginBinding inflate(@NonNull LayoutInflater inflater) {
return inflate(inflater, null, false);
}
@NonNull
public static FragmentLoginBinding inflate(@NonNull LayoutInflater inflater,
@Nullable ViewGroup parent, boolean attachToParent) {
View root = inflater.inflate(R.layout.fragment_login, parent, false);
if (attachToParent) {
parent.addView(root);
}
return bind(root);
}
@NonNull
public static FragmentLoginBinding bind(@NonNull View rootView) {
// The body of this method is generated in a way you would not otherwise write.
// This is done to optimize the compiled bytecode for size and performance.
String missingId;
missingId: {
Button btnLogin = rootView.findViewById(R.id.btn_login);
if (btnLogin == null) {
missingId = "btnLogin";
break missingId;
}
return new FragmentLoginBinding((ConstraintLayout) rootView, btnLogin);
}
throw new NullPointerException("Missing required view with ID: ".concat(missingId));
}
}
在Fragment中使用如下:
class LoginFragment :Fragment(),View.OnClickListener{
private var loginBinding:FragmentLoginBinding?=null
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
loginBinding = FragmentLoginBinding.inflate(inflater,container,false)
return loginBinding?.root
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
loginBinding?.btnLogin?.text = "登录完成"
loginBinding?.btnLogin?.setOnClickListener(this)
}
override fun onClick(v: View?) {
when(v){
loginBinding?.btnLogin-> Toast.makeText(activity,"click login btn", Toast.LENGTH_SHORT).show()
}
}
override fun onDestroyView() {
loginBinding = null
super.onDestroyView()
}
}
我们新建了一个fragment_login.xml的布局,运行会自动帮我们生成FragmentLoginBinding类,在Fragment中使用,在onCreateView里调用FragmentLoginBinding.inflate(inflater,container,false),并把loginBinding的最外层布局返回。在onDestroyView里置空loginBinding。
五:不生成Binding类的配置
上面我们讲到,新建个布局,重新编译,会自动帮我们创建对应的Binding类,如果我们不想生成呢。那么只需要在跟布局添加上 tools:viewBindingIgnore="true" 即可。代码如下:
<FrameLayout
tools:viewBindingIgnore="true">
</FrameLayout>