一、kotlin-android-extensions??????

????????在使用ViewBinding之前，我們一直使用的是kotlin-android-extensions，使用kotlin-android-extensions可以節約很多寫findViewById的時間。不過這個kotlin-android-extensions插件已經廢棄了，簡單說一下kotlin-android-extensions存在的問題：

????????1.通過反編譯kotlin-android-extensions的代碼，發現會創建一個HashMap，用來存放所有的id和對應的View的緩存，如果緩存中沒有View，那么就通過findViewById去創建并存入緩存，否則就直接獲取。所以會存在內存問題。

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();} }// $FF: synthetic method public void onDestroyView() {super.onDestroyView();this._$_clearFindViewByIdCache(); }

????????2.由于kotlin-android-extensions是通過view的id名直接引用的，如果多個布局間的同名id，就需要手動對import進行重命名處理，如果引用錯誤的布局文件，就會出現crash。所以存在資源重名的問題。

????????3.只有Kotlin才可以使用。

????????所以ViewBinding優勢有：java,kotlin都可以使用，可以有效避免NullPointerException。

二、ViewBinding

ViewBinding使用

1.gradle配置

buildFeatures {viewBinding true }

? ????????開啟ViewBinding之后，在編譯時，AGP會自動幫我們給每個xml布局創建一個Binding類，位于build/generated/data_binding_base_class_source_out/目錄下。

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.因為這些類編譯時就生成了，就不會占用運行時內存。

2.未使用的Binding文件會在混淆時被刪除，所以對包大小影響很小。

3.編譯器生成Binding文件是增量更新的。

那么如何不生成Binding類呢？tools:viewBindingIgnore="true"

<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:viewBindingIgnore="true"tools:context=".MainActivity">

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"} }

<?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"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".testviewbinding.TestViewBindingActivity"><TextViewandroid:id="@+id/titleTv"android:layout_width="match_parent"android:layout_height="100dp"android:gravity="center"android:text="在Activity中使用ViewBinding"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout>

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)} }

? ? ?

<?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".testviewbinding.TextViewBindingFragment"><TextViewandroid:id="@+id/tvTitle"android:layout_width="match_parent"android:layout_height="match_parent"android:text="在Fragment中" /></FrameLayout>

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<String>("1", "2", "3", "4", "5", "6")}private fun initView() {with(binding.contentRcycler) {layoutManager = GridLayoutManager(context, 4)adapter = TestRecyclerViewAdapter(ITEMS)}} } <?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".testviewbinding.TestAdapterActivity"><androidx.recyclerview.widget.RecyclerViewandroid:id="@+id/contentRcycler"android:layout_width="match_parent"android:layout_height="match_parent" /> </androidx.constraintlayout.widget.ConstraintLayout>

class TestRecyclerViewAdapter(private val values: List<String>) :RecyclerView.Adapter<TestRecyclerViewAdapter.ViewHolder>() {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 }

<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="200dp"><TextViewandroid:id="@+id/contentTv"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:textSize="16dp"tools:text="99" /> </androidx.constraintlayout.widget.ConstraintLayout>

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)}} <?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"><TextViewandroid:id="@+id/dialogContent"android:layout_width="200dp"android:layout_height="200dp"android:text="This is Dialog"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent" /></androidx.constraintlayout.widget.ConstraintLayout>

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"} }<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".testviewbinding.TestIncludeActivity"><includeandroid:id="@+id/itemInclude"layout="@layout/item_layout" /> </androidx.constraintlayout.widget.ConstraintLayout>

<?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"><TextViewandroid:id="@+id/itemContentTv"android:layout_width="match_parent"android:layout_height="200dp"android:text="Test include"android:textSize="30sp"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent" /></androidx.constraintlayout.widget.ConstraintLayout>

三、ViewBinding封裝

1.在BaseActivity中封裝

abstract class BaseViewBindingActivity<T : ViewBinding> : 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<ActivityChildViewBindingMainBinding>() {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)} } <?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"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".encapsulatviewbinding.ChildViewBindingMainActivity"><TextViewandroid:id="@+id/titleTv"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:text="36sp" /> </androidx.constraintlayout.widget.ConstraintLayout>

2.通過反射的方式封裝

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

<?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"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".encapsulatviewbinding.TestViewBindingMainActivity"><TextViewandroid:id="@+id/titleTv"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center"android:textSize="36sp" /> </androidx.constraintlayout.widget.ConstraintLayout>

3.反射+基類

1.在Activity 中使用

abstract class BaseBindingMainActivity2<T : ViewBinding> : 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 Class<T>val method = clazz.getMethod("inflate", LayoutInflater::class.java)binding = method.invoke(null, layoutInflater) as T}setContentView(binding.root)} }

class ChildViewBindingMainActivity2 :BaseBindingMainActivity2<ActivityChildViewBindingMain2Binding>() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding.titleTv.text = "哈哈，這是反射+基類的方式"} }

<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".encapsulatviewbinding.ChildViewBindingMainActivity2"><TextViewandroid:id="@+id/titleTv"android:layout_width="match_parent"android:layout_height="match_parent" /> </androidx.constraintlayout.widget.ConstraintLayout>

2.在Fragment中使用

abstract class BaseBindingViewFragment<T : ViewBinding> : 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 Class<T>val 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<FragmentChildBindingBinding>() {override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?): View? {return super.onCreateView(inflater, container, savedInstanceState)}companion object {@JvmStaticfun newInstance() = ChildBindingFragment()} }

class TestBindingMainActivity3 : BaseBindingMainActivity2<ActivityTestBindingMain3Binding>() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)val newInstance = ChildBindingFragment.newInstance()addFragment(supportFragmentManager,newInstance,isAllowStateLoss = true,frameId = R.id.frame)} }

<?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".encapsulatviewbinding.ChildBindingFragment"><TextViewandroid:layout_width="match_parent"android:layout_height="match_parent"android:text="@string/hello_blank_fragment" /></FrameLayout>

4.委托的方式

class TestViewBindingFragment2 : Fragment(R.layout.fragment_test_view_binding2) {private val binding by inflate<FragmentTestViewBinding2Binding>()override fun onViewCreated(view: View, savedInstanceState: Bundle?) {super.onViewCreated(view, savedInstanceState)binding.root}companion object {@JvmStaticfun newInstance() = TestViewBindingFragment2()} }inline fun <reified T : ViewBinding> Fragment.inflate() =FragmentViewBindingDelegate(T::class.java)class FragmentViewBindingDelegate<T : ViewBinding>(private val clazz: Class<T>) :ReadOnlyProperty<Fragment, T> {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!!}}

<?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".encapsulatviewbinding.TestViewBindingFragment2"><TextViewandroid:layout_width="match_parent"android:layout_height="match_parent"android:text="8888888" /></FrameLayout>

總結

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