Kotlin中使用view binding2020-11-30

本文翻译自：https://johncodeos.com/how-to-use-view-binding-in-android-using-kotlin/

Android Stuido4.1中，移除了kotlin-android-extensions插件

所以不能在.kt文件中使用Kotlinx synthetic语法了

替代方案有：

• ButterKnife
• findViewById()
• View Binding

下面看下View Binding在下面的场景怎么使用

• Activities
• Fragments:
  • Inflate
  • Bind
• RecyclerView Adapter

一、Enabling View Binding

android {

    // module级别的build.gradle文件中添加下名的配置
    // 会自动为xml文件生成binding class
    // 命名规则是Pascal case  + Binding
    // 可在XML中添加属性来屏蔽生成binding class
    // tools:viewBindingIgnore="true"
    buildFeatures {
        viewBinding true
    }
}

二、Using View Binding in Activities

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        val view = binding.root
        setContentView(view)
       
        // ...

    }
}


binding.myButton.setOnClickListener { // Button Tapped }
binding.myTextView.text = "View Binding is the best!"

三、Using View Binding in Fragments

inflate methos

class DemoInflateFragment : Fragment() {

    private var fragmentDemoBinding: FragmentDemoBinding? = null

    // 注意是在onCreateView中inflate内容，所以AsyncLayoutInflater不适应Fragment
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val binding = FragmentDemoBinding.inflate(inflater, container, false)
        fragmentDemoBinding = binding

        binding.myButton.setOnClickListener {
             // Button Tapped
        }
   
        binding.myTextView.text = "View Binding is the best!"

        return binding.root
    }
    override fun onDestroyView() {
        // View不见时Fragment可以存在
        fragmentDemoBinding = null
        super.onDestroyView()
    }  
}

Bind method

class DemoBindFragment : Fragment(R.layout.fragment_demo) {

    private var fragmentDemoBinding: FragmentDemoBinding? = null

    // 构造方法中传入了，resId，默认的onCreateView中会inflate内容，此时只需要bind即可
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        val binding = FragmentDemoBinding.bind(view)
        fragmentDemoBinding = binding

        binding.myButton.setOnClickListener { // Button Tapped }
        binding.myTextView.text = "View Binding is the best!"
    }
    override fun onDestroyView() {
        // View不见时Fragment可以存在
        fragmentDemoBinding = null
        super.onDestroyView()
    }        
}

四、Using View Binding in RecycleView Adapter

class Items_RVAdapter(private var itemsCells: ArrayList<String?>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    
     // 第一步，使用binding class作为root layout
    class ItemViewHolder(var viewBinding: ItemRowBinding) : RecyclerView.ViewHolder(viewBinding.root)

    // 第二步，inflate内容并返回ItemViewHolder
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val binding = ItemRowBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        return ItemViewHolder(binding)
    }
    // 第三步，直接使用了
    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        val itemViewHolder = holder as ItemViewHolder
        itemViewHolder.viewBinding.itemtextview.text = itemsCells[position]
    }

}