Jetpack系列(八) — Data Bidnding && View Binding-一一网

Jetpack系列(八) — Data Bidnding && View Binding

Hilt 简单介绍

初步印象

Data Bidnding , 包含View Binding 所有功能，支持双向绑定

View Binding 仅仅支持绑定 View，kotlin-android-extensions 插件的替代方案

Data Bidnding和View Binding可以同时存在

Data Bidnding性能劣于View Binding，因此一些项目当中仅仅使用View Binding

基本概念

我只打算使用View Binding替代findViewById()，Data Bidnding了解即可

基本使用

View Binding 基本使用

将 viewBinding 元素添加到其 build.gradle 文件中

android {
    ...
    viewBinding {
        enabled = true
    }
}
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在 Activity 中使用视图绑定

在 Activity 的 onCreate() 方法，调用生成的绑定类中包含的静态 inflate() 方法
用binding.控件Id 操作控件

// MainActivity
class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // 自动生成
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
    }    
}
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在 Fragment 中使用视图绑定

请在 Fragment 的 onCreateView()方法中执行，调用生成的绑定类中包含的静态 inflate() 方法

class DeepLinkFragment : Fragment() {

    private var _binding: FragmentDeepLinkBinding? = null
    private val binding
        get() = _binding!!

    private val mainViewModel: MainViewModel by activityViewModels()

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = FragmentDeepLinkBinding.inflate(inflater, container, false)
        return binding.root
    }
 
    override fun onDestroy() {
        super.onDestroy()
        _binding = null
    }
}
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在Adapter中使用ViewBinding

通过绑定类inflate 方法传入ViewHolder

// WordListAdapter.kt
class WordListAdapter : ListAdapter<Word, WordViewHolder>(WORDS_COMPARATOR) {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): WordViewHolder =
        WordViewHolder.create(parent)

    override fun onBindViewHolder(holder: WordViewHolder, position: Int) {
        val item = getItem(position)
        holder.bind(item)
    }

    companion object {
        private val WORDS_COMPARATOR = object : DiffUtil.ItemCallback<Word>() {
            override fun areItemsTheSame(oldItem: Word, newItem: Word): Boolean =
                oldItem == newItem

            override fun areContentsTheSame(oldItem: Word, newItem: Word): Boolean =
                oldItem.word == newItem.word

        }
    }

}

class WordViewHolder(binding: ItemWordBinding) : RecyclerView.ViewHolder(binding.root) {

    private val textView: TextView = binding.textView

    fun bind(word: Word?) {
        textView.text = word?.word?:""
    }

    companion object {
        fun create(parent: ViewGroup): WordViewHolder {
            val binding =
                ItemWordBinding.inflate(LayoutInflater.from(parent.context), parent, false)
            return WordViewHolder(binding)
        }
    }
}
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Data Binding 基本使用

修改 build.gradle 文件

dataBinding {
    enabled = true
}
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生成data binding布局，参见知识点三

这里我实现一下点击刷新的效果
点击事件onClick="@{()-> model.updateTaps()}"

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

    <data>
        <variable
            name="model"
            type="com.huang.myapplication.viewmodel.MainViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/home_contain"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ui.main.home.HomeFragment">
 
        <Button
            android:id="@+id/btn_add"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginStart="10dp"
            android:layout_marginTop="10dp"
            android:layout_marginEnd="10dp"
            android:text="@string/refresh"
            android:onClick="@{()-> model.updateTaps()}"
            app:layout_constraintHorizontal_weight="1"
            app:layout_constraintLeft_toRightOf="@+id/btn_next"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tv_count"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="10dp"
            android:text="@{model.taps}"
            app:layout_constraintBottom_toBottomOf="@+id/tv_current_count"
            app:layout_constraintLeft_toRightOf="@+id/tv_current_count"
            app:layout_constraintTop_toTopOf="@+id/tv_current_count" />

 
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>
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再viewmodel当中观察数据

class MainViewModel @Inject constructor(
    private val repository: WordRepository
) : ViewModel() {

    private var _tapCount = 0
    private var _taps = MutableLiveData<String>("$_tapCount taps")
   
    val taps: LiveData<String> =  _taps

    fun updateTaps() {
        _tapCount++
        _taps.value = "$_tapCount taps"
    }
}
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绑定视图

Activity生成binding 视图类

 // 方式一： 
 val binding: ActivityXxxBinding = DataBindingUtil.setContentView(
     this, R.layout.activity_main)

 // 方式二： 
 val binding: ActivityXxxBinding = ActivityMainBinding.inflate(getLayoutInflater())
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Fragment、ListView 或 RecyclerView 适配器中使用数据绑定项

// 方式一：  
val listItemBinding = ListItemBinding.inflate(layoutInflater, viewGroup, false)

// 方式二： 
val listItemBinding = DataBindingUtil.inflate(layoutInflater,R.layout.list_item, viewGroup, false)
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可以使用 LiveData对象作为数据绑定来源，自动将数据变化通知给界面，需要binding.lifecycleOwner = this 设置视图绑定类的生命周期

class HomeFragment : Fragment() {

    private var _binding: FragmentHomeBinding? = null
    private val binding
        get() = _binding!!

    private lateinit var adapter: WordListAdapter

    private val mainViewModel: MainViewModel by activityViewModels()

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = DataBindingUtil.inflate(layoutInflater, R.layout.fragment_home,container, false)
        setHasOptionsMenu(true)
        binding.lifecycleOwner = this
        return binding.root
    }

    override fun onDestroy() {
        super.onDestroy()
        _binding = null
    }
}
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