Android|Android ViewBinding使用介绍 AndroidViewBinding使用介绍

一、kotlin-android-extensions
二、ViewBinding使用

1.gradle配置
2.在Activity 使用
3.在Fragment使用
4.在Adapter中使用
5.在Dialog中使用
6.Include中使用

三、ViewBinding封装

1.在BaseActivity中封装
2.通过反射的方式封装
3.反射+基类

1.在Activity 中使用
2.在Fragment中使用

4.委托的方式

一、kotlin-android-extensions 在使用ViewBinding之前，我们一直使用的是kotlin-android-extensions，使用kotlin-android-extensions可以节约很多写findViewById的时间。不过这个kotlin-android-extensions插件已经废弃了，简单说一下kotlin-android-extensions存在的问题：
1.通过反编译kotlin-android-extensions的代码，发现会创建一个HashMap，用来存放所有的id和对应的View的缓存，如果缓存中没有View，那么就通过findViewById去创建并存入缓存，否则就直接获取。所以会存在内存问题。

private HashMap _$_findViewCache; public View _$_findCachedViewById(int var1) {if (this._$_findViewCache == null) {this._$_findViewCache = new HashMap(); }View var2 = (View)this._$_findViewCache.get(var1); if (var2 == null) {View var10000 = this.getView(); if (var10000 == null) {return null; }var2 = var10000.findViewById(var1); this._$_findViewCache.put(var1, var2); }return var2; }public void _$_clearFindViewByIdCache() {if (this._$_findViewCache != null) {this._$_findViewCache.clear(); }}// $FF: synthetic methodpublic void onDestroyView() {super.onDestroyView(); this._$_clearFindViewByIdCache(); }

2.由于kotlin-android-extensions是通过view的id名直接引用的，如果多个布局间的同名id，就需要手动对import进行重命名处理，如果引用错误的布局文件，就会出现crash。所以存在资源重名的问题。
3.只有Kotlin才可以使用。
【Android|Android ViewBinding使用介绍】所以ViewBinding优势有：java,kotlin都可以使用，可以有效避免NullPointerException。

二、ViewBinding使用
1.gradle配置

buildFeatures {
viewBinding true
}

开启ViewBinding之后，在编译时，AGP会自动帮我们给每个xml布局创建一个Binding类，位于build/generated/data_binding_base_class_source_out/目录下。

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public final class FragmentLoginBinding implements ViewBinding {@NonNullprivate final ConstraintLayout rootView; @NonNullpublic final ConstraintLayout container; @NonNullpublic final ProgressBar loading; @NonNullpublic final Button login; @NonNullpublic final EditText password; @NonNullpublic final EditText username; private FragmentLoginBinding(@NonNull ConstraintLayout rootView,@NonNull ConstraintLayout container, @NonNull ProgressBar loading, @NonNull Button login,@NonNull EditText password, @NonNull EditText username) {this.rootView = rootView; this.container = container; this.loading = loading; this.login = login; this.password = password; this.username = username; }@Override@NonNullpublic ConstraintLayout getRoot() {return rootView; }@NonNullpublic static FragmentLoginBinding inflate(@NonNull LayoutInflater inflater) {return inflate(inflater, null, false); }@NonNullpublic 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); }@NonNullpublic 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.int id; missingId: {ConstraintLayout container = (ConstraintLayout) rootView; id = R.id.loading; ProgressBar loading = rootView.findViewById(id); if (loading == null) {break missingId; }id = R.id.login; Button login = rootView.findViewById(id); if (login == null) {break missingId; }id = R.id.password; EditText password = rootView.findViewById(id); if (password == null) {break missingId; }id = R.id.username; EditText username = rootView.findViewById(id); if (username == null) {break missingId; }return new FragmentLoginBinding((ConstraintLayout) rootView, container, loading, login,password, username); }String missingId = rootView.getResources().getResourceName(id); throw new NullPointerException("Missing required view with ID: ".concat(missingId)); }}

注意：
1.因为这些类编译时就生成了，就不会占用运行时内存。
2.未使用的Binding文件会在混淆时被删除，所以对包大小影响很小。
3.编译器生成Binding文件是增量更新的。
那么如何不生成Binding类呢？tools:viewBindingIgnore="true"

2.在Activity 使用

class TestViewBindingActivity : AppCompatActivity() {private lateinit var bindding: ActivityTestViewBindingBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)bindding = ActivityTestViewBindingBinding.inflate(layoutInflater)setContentView(bindding.root)changeText()}private fun changeText() {bindding.titleTv.text = "哈哈，在Activity中使用ViewBinding了"}}

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3.在Fragment使用

class TextViewBindingFragment : Fragment() {private var param1: String? = nullprivate var param2: String? = nullprivate var _binding: FragmentTextViewBindingBinding? = nullprivate val binding get() = _binding!!override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)arguments?.let {param1 = it.getString(ARG_PARAM1)param2 = it.getString(ARG_PARAM2)}}override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?): View? {_binding = FragmentTextViewBindingBinding.inflate(layoutInflater, container, false)return binding.root}override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)changeText()}private fun changeText() {binding.tvTitle.text = "哈哈，在Fragment中使用ViewBinding"}override fun onDestroyView() {super.onDestroyView()_binding = null}companion object {@JvmStaticfun newInstance(param1: String, param2: String) =TextViewBindingFragment().apply {arguments = Bundle().apply {putString(ARG_PARAM1, param1)putString(ARG_PARAM2, param2)}}@JvmStaticfun newInstance() = TextViewBindingFragment()}}

class TestViewBindingActivity : AppCompatActivity() {private lateinit var bindding: ActivityTestViewBindingBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)bindding = ActivityTestViewBindingBinding.inflate(layoutInflater)setContentView(bindding.root)val newInstance = TextViewBindingFragment.newInstance()addFragment(supportFragmentManager,newInstance,isAllowStateLoss = true,frameId = R.id.fragmentFrame)}}

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4.在Adapter中使用

class TestAdapterActivity : AppCompatActivity() {private lateinit var binding: ActivityTestAdapterBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding = ActivityTestAdapterBinding.inflate(layoutInflater)setContentView(binding.root)initView()}companion object {val ITEMS = mutableListOf("1", "2", "3", "4", "5", "6")}private fun initView() {with(binding.contentRcycler) {layoutManager = GridLayoutManager(context, 4)adapter = TestRecyclerViewAdapter(ITEMS)}}}

class TestRecyclerViewAdapter(private val values: List) :RecyclerView.Adapter() {inner class ViewHolder(binding: RecyclerItemLayoutBinding) :RecyclerView.ViewHolder(binding.root) {val textTv = binding.contentTv}override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {return ViewHolder(RecyclerItemLayoutBinding.inflate(LayoutInflater.from(parent.context),parent,false))}override fun onBindViewHolder(holder: ViewHolder, position: Int) {val item = values[position]holder.textTv.text = item}override fun getItemCount(): Int = values.size}

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5.在Dialog中使用

class CommonDialog(context: Context) : Dialog(context) {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(DialogLayoutBinding.inflate(layoutInflater).root)}}

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6.Include中使用

class TestIncludeActivity : AppCompatActivity() {private lateinit var binding: ActivityTestIncludeBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding = ActivityTestIncludeBinding.inflate(layoutInflater)setContentView(binding.root)initView()}private fun initView() {binding.itemInclude.itemContentTv.text = "哈哈， this is include"}}

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三、ViewBinding封装
1.在BaseActivity中封装

abstract class BaseViewBindingActivity : AppCompatActivity() {protected val binding by lazy {getViewBinding()}override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(binding.root)}protected abstract fun getViewBinding(): T}

class ChildViewBindingMainActivity :BaseViewBindingActivity() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding.titleTv.text = "哈哈，this is child binding activity"}override fun getViewBinding(): ActivityChildViewBindingMainBinding {return ActivityChildViewBindingMainBinding.inflate(layoutInflater)}}

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2.通过反射的方式封装

class TestViewBindingMainActivity : AppCompatActivity() {private val binding by inflate()override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding.titleTv.text = "哈哈，通过反射封装ViewBinding"}}inline fun inflateByViewBinding(layoutInflater: LayoutInflater) =T::class.java.getMethod("inflate", LayoutInflater::class.java).invoke(null, layoutInflater) as Tinline fun Activity.inflate() = lazy {inflateByViewBinding(layoutInflater).apply {setContentView(root)}}

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3.反射+基类

1.在Activity 中使用

abstract class BaseBindingMainActivity2 : AppCompatActivity() {protected lateinit var binding: Toverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)val type = javaClass.genericSuperclassif (type is ParameterizedType) {val clazz = type.actualTypeArguments[0] as Classval method = clazz.getMethod("inflate", LayoutInflater::class.java)binding = method.invoke(null, layoutInflater) as T}setContentView(binding.root)}}

class ChildViewBindingMainActivity2 :BaseBindingMainActivity2() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding.titleTv.text = "哈哈，这是反射+基类的方式"}}

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2.在Fragment中使用

abstract class BaseBindingViewFragment : Fragment() {private var _binding: T? = nullprotected val binding get() = _binding!!override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?): View? {val type = javaClass.genericSuperclassval clazz = (type as ParameterizedType).actualTypeArguments[0] as Classval method = clazz.getMethod("inflate",LayoutInflater::class.java,ViewGroup::class.java,Boolean::class.java)_binding = method.invoke(null, layoutInflater, container, false) as Tthis.viewLifecycleOwner.lifecycle.addObserver(object : LifecycleEventObserver {override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {if (event == Lifecycle.Event.ON_DESTROY) {Log.v(TAG, "onDestroy binding be null")_binding = null}}})return binding.root}companion object {const val TAG = "BaseBindingViewFragment"}}

class ChildBindingFragment : BaseBindingViewFragment() {override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?): View? {return super.onCreateView(inflater, container, savedInstanceState)}companion object {@JvmStaticfun newInstance() = ChildBindingFragment()}}

class TestBindingMainActivity3 : BaseBindingMainActivity2() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)val newInstance = ChildBindingFragment.newInstance()addFragment(supportFragmentManager,newInstance,isAllowStateLoss = true,frameId = R.id.frame)}}

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4.委托的方式

class TestViewBindingFragment2 : Fragment(R.layout.fragment_test_view_binding2) {private val binding by inflate()override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)binding.root}companion object {@JvmStaticfun newInstance() = TestViewBindingFragment2()}}inline fun Fragment.inflate() =FragmentViewBindingDelegate(T::class.java)class FragmentViewBindingDelegate(private val clazz: Class) :ReadOnlyProperty {private var binding: T? = nulloverride fun getValue(thisRef: Fragment, property: KProperty<*>): T {if (binding == null) {binding =clazz.getMethod("bind", View::class.java).invoke(null, thisRef.requireView()) as TthisRef.viewLifecycleOwner.lifecycle.addObserver(object : LifecycleEventObserver {override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {if (event == Lifecycle.Event.ON_DESTROY) {binding = null}}})}return binding!!}}