ViewBinding
一旦启动了ViewBinding功能之后,Android Studio会自动为我们所编写的每一个布局文件都生成一个对应的Binding类。
启用ViewBinding需要在app/build.gradle中添加
android {
...
buildFeatures {
viewBinding true
}
}
Binding类的命名规则是将布局文件按驼峰方式重命名后,再加上Binding作为结尾。
比如说,我们定义一个activity_main.xml布局,那么与它对应的Binding类就是ActivityMainBinding。
当然,如果有些布局文件你不希望为它生成对应的Binding类,可以在该布局文件的根元素位置加入如下声明:
<LinearLayout
xmlns:tools="http://schemas.android.com/tools"
...
tools:viewBindingIgnore="true">
...
</LinearLayout>
1. 在Activity中使用ViewBinding
class FirstActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val binding = ActivityFirstBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.button1.text = "Hello World!"
binding.button1.setOnClickListener {
Toast.makeText(this, "Button clicked.", Toast.LENGTH_SHORT).show()
}
}
}
如果需要在onCreate()函数之外的地方对空间进行控制,将binding变量声明为全局变量
Kotlin声明的变量都必须在声明的同时对其进行初始化。而这里我们显然无法在声明全局binding变量的同时对它进行初始化,所以这里又使用了lateinit关键字对binding变量进行了延迟初始化。
class FirstActivity : AppCompatActivity() {
private lateinit var binding: ActivityFirstBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityFirstBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.button1.text = "Hello World!"
binding.button1.setOnClickListener {
Toast.makeText(this, "Button clicked.", Toast.LENGTH_SHORT).show()
}
}
}
2. 在Fragment中使用ViewBinding
通过以下方法来实现在MainFragment中显示布局
class MainFragment : Fragment(){
private var _binding : FragmentMainBinding? = null
val binding get() = _binding!!
override fun onCreateView(inflater : LayoutInflater, container : ViewGroup?, savedInstanceState : Bundle?) : View{
_binding = FragmentMainBinding.inflate(inflater, container, false)
return binding.root
}
override fun onDestroyView(){
super.onDestroyView()
_binding = null
}
}
由于我们是在onCreateView()函数中加载的布局,那么理应在与其对应的onDestroyView()函数中对binding变量置空,从而保证binding变量的有效生命周期是在onCreateView()函数和onDestroyView()函数之间。
3. 在Adapter中使用ViewBinding
假设我们定义了fruit_item.xml来作为RecyclerView的子项布局
编写如下RecyclerView Adapter来加载和显示这个子项布局
class FruitAdapter(val fruitList : List<Fruit>) : RecyclerView.Adapter<FruitAdapter.ViewHolder>(){
inner class ViewHolder(view : View) : RecyclerView.ViewHolder(view){
val fruitImage : ImageView = view.findViewById(R.id.fruitImage)
val fruitName : TextView = view.findViewById(R.id.fruitName)
}
override fun onCreateViewHolder(parent : ViewGroup, ViewType : Int) : ViewHolder{
val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder : ViewHolder, position : Int){
val fruit = fruitList[position]
holder.fruitImage.setImageResource(fruit.imageId)
holder.fruitName.text = fruit.name
}
override fun getItemCount() = fruitList.size
}
接下来在Adapter中使用ViewBinding
class FruitAdapter(val fruitList : List<Fruit>) : RecyclerView.Adapter<FruitAdapter.ViewHolder>(){
inner class ViewHolder(binding : FruitItemBinding) : RecyclerView.ViewHolder(binding.root){
val fruitImage : ImageView = binding.fruitImage
val fruitName : TextView = binding.fruitName
}
override fun onCreateViewHolder(parent : ViewGroup, ViewType : Int) : ViewHolder{
val binding = FruitItemBinding.inflate(LayoutInflter.from(parent.context), parent, false)
return ViewHolder(binding)
}
override fun onBindViewHolder(holder : ViewHolder, position : Int){
val fruit = fruitList[position]
holder.fruitImage.setImageResource(fruit.imageId)
holder.fruitName.text = fruit.name
}
override fun getItemCount() = fruitList.size
}
- 我们在onCreateViewHolder()函数中调用FruitItemBinding的inflate()函数去加载fruit_item.xml布局文件。
- 接下来需要改造ViewHolder,让其构造函数接收FruitItemBinding这个参数。但是注意,ViewHolder的父类RecyclerView.ViewHolder它只会接收View类型的参数,因此我们需要调用binding.root获得fruit_item.xml中根元素的实例传给RecyclerView.ViewHolder。
4. 对引入布局使用ViewBinding
假设我们有一titlebar.xml作为通用布局引入到其他布局中
1. 使用include引入布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
...
<include
<!--在include的时候给被引入的布局添加一个id,ViewBinding便可以关联到titlebar.xml中的控件-->
android:id="@+id/titleBar"
layout="@layout/titlebar" />
...
</LinearLayout>
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.titleBar.title.text = "Title"
binding.titleBar.back.setOnClickListener {
}
binding.titleBar.done.setOnClickListener {
}
}
}
2. 使用merge引入布局
使用merge标签引入的布局在某些情况下可以减少一层布局的嵌套,而更少的布局嵌套通常就意味着更高的效率
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<Button
android:id="@+id/back"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:text="Back" />
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Title"
android:textSize="20sp" />
<Button
android:id="@+id/done"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:text="Done" />
</merge>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
...
<include
layout="@layout/titlebar" />
...
</LinearLayout>
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
private lateinit var titlebarBinding: TitlebarBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
titlebarBinding = TitlebarBinding.bind(binding.root)
setContentView(binding.root)
titlebarBinding.title.text = "Title"
titlebarBinding.back.setOnClickListener {
}
titlebarBinding.done.setOnClickListener {
}
}
}
5. 在自定义控件中使用ViewBinding
自定义导航栏
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@drawable/title_bg">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/titleBack"
android:text="back"
android:layout_margin="5dp"
android:background="@drawable/back_bg"
android:textColor="#fff"/>
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:id="@+id/titleText"
android:layout_weight="1"
android:layout_gravity="center"
android:gravity="center"
android:text="Title Text"
android:textColor="#fff"
android:textSize="24sp"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/titleEdit"
android:text="Edit"
android:layout_margin="5dp"
android:background="@drawable/edit_bg"
android:textColor="#fff"/>
</LinearLayout>
添加自定义控件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.android.widgettest.TitleLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
使用ViewBinding
class TitleLayout(context : Context, attrs : AttributeSet) : LinearLayout(context, attrs) {
var binding : TitleBinding
init {
binding = TitleBinding.inflate(LayoutInflater.from(context), this, true)
binding.titleBack.setOnClickListener {
val activity = context as Activity
activity.finish()
}
binding.titleEdit.setOnClickListener {
Toast.makeText(context, "Edit", Toast.LENGTH_SHORT).show()
}
}
}
6. 在Activity中获取fragment的binding对象
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<fragment
android:id="@+id/leftFrag"
android:name="com.android.fragment.LeftFragment"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"/>
</LinearLayout>
fragment_one.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button"
android:layout_gravity="center_horizontal"
android:text="button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
OneFragment.kt
class OneFragment : Fragment() {
private var _binding : LeftFragmentBinding? = null
val binding get() = _binding!!
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
_binding = LeftFragmentBinding.inflate(inflater, container, false)
return binding.root
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
MainActivity.kt
class MainActivity : AppCompatActivity() {
lateinit var binding : ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
val leftFrag = supportFragmentManager.findFragmentById(R.id.leftFrag) as LeftFragment
leftFrag.binding.button.setOnClickListener {
Log.d("TestBtn", "clicked")
}
}
}
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