Android View Binding的使用

什么是View Binding

官方文檔

View Binding是Android Studio 3.6推出的新特性,目的是為了替代findViewById(內部實現(xiàn)還是使用findViewById)。。在啟動視圖綁定后,系統(tǒng)會為改模塊中的每個xml文件生成一個綁定類,綁定類的實例包含對在相應布局中具有 ID 的所有視圖的直接引用。

View Binding 的優(yōu)點

  • Null 安全:由于視圖綁定會創(chuàng)建對視圖的直接引用,因此不存在因視圖 ID 無效而引發(fā) Null 指針異常的風險。此外,如果視圖僅出現(xiàn)在布局的某些配置中,則綁定類中包含其引用的字段會使用 @Nullable 標記。
  • 類型安全:每個綁定類中的字段均具有與它們在 XML 文件中引用的視圖相匹配的類型。這意味著不存在發(fā)生類轉換異常的風險。

如何啟用View Binding 功能

android {
        ...
        viewBinding {
            enabled = true
        }
    }
} 

如果想在生成綁定類時忽略某個布局文件,將 tools:viewBindingIgnore="true" 屬性添加到相應布局文件的根視圖中:

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

怎么去使用View Binding

為用視圖綁定功能后,系統(tǒng)會為該模塊中包含的每個 XML 布局文件生成一個綁定類。這個類的類名是以xml布局文件名去掉下?lián)Q線后,單詞首字母大寫加上Binding命名的。如activity_main.xml生成的類ActivityMainBinding.

  • 如何在Activity中設置綁定,請在 Activity 的 onCreate() 方法中執(zhí)行以下步驟:

    1. 調用生成的綁定類中包含的靜態(tài) inflate() 方法。此操作會創(chuàng)建該綁定類的實例以供 Activity 使用。

    2. 通過調用 getRoot() 方法或使用 Kotlin 屬性語法獲取對根視圖的引用。

    3. 將根視圖傳遞到 setContentView(),使其成為屏幕上的活動視圖。

    //activity_main.xml
    <?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=".MainActivity">
    
        <Button
            android:id="@+id/button"
            android:layout_width="100dp"
            android:layout_height="40dp"
            android:text="這是按鈕"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView" />
    
    
        <TextView
            android:id="@+id/textView"
            android:layout_width="100dp"
            android:layout_height="40dp"
            android:gravity="center"
            android:text="Hello World!"
            app:layout_constraintBottom_toTopOf="@+id/button"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    
    </androidx.constraintlayout.widget.ConstraintLayout>  
    
    //MainActivity.java
    public class MainActivity extends AppCompatActivity {
        private ActivityMainBinding binding;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            //關鍵代碼
            binding = ActivityMainBinding.inflate(getLayoutInflater());
            View rootView = binding.getRoot();
            setContentView(rootView);
            //如何使用
            binding.textView.setText("這是修改的");
            binding.button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Log.d("Main","點擊了按鈕");
                }
            });
    
        }
    }
    
  • 如何在 Fragment 中使用視圖綁定 請在 Fragment 的 onCreateView()方法中執(zhí)行以下步驟(注意:Fragment 的存在時間比其視圖長。請務必在 Fragment 的 onDestroyView() 方法中清除對綁定類實例的所有引用。)

    1. 調用生成的綁定類中包含的靜態(tài) inflate() 方法。此操作會創(chuàng)建該綁定類的實例以供 Fragment 使用。

    2. 通過調用 getRoot() 方法或使用 Kotlin 屬性語法獲取對根視圖的引用。

    3. onCreateView() 方法返回根視圖,使其成為屏幕上的活動視圖。

      如果view已經創(chuàng)建可以在onViewCreated()中使用bind(view)方法。官方示例

    //fragment_my.xml
    <?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=".MainActivity">
    
        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="40dp"
            android:text="這是Fragment按鈕"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView" />
    
    
        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="40dp"
            android:gravity="center"
            android:text="這是FragmentTextView"
            app:layout_constraintBottom_toTopOf="@+id/button"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    
    </androidx.constraintlayout.widget.ConstraintLayout>
    
    public class MyFragment extends Fragment {
      private FragmentMyBinding binding;
    
      public MyFragment() {
    
      }
    
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
    
      }
    
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
                               Bundle savedInstanceState) {
          binding = FragmentMyBinding.inflate(inflater, container, false);
          return binding.getRoot();
      }
    
      @Override
      public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
          super.onViewCreated(view, savedInstanceState);
          binding.textView.setText("這是Fragment");
          binding.button.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  Log.d("Fragment", "點擊了按鈕");
              }
          });
      }
    
      @Override
      public void onDestroy() {
          super.onDestroy();
          binding = null;
      }
    
    
    //在onViewCreated中使用View Binding
    public class MyFragment extends Fragment {
      private FragmentMyBinding binding;
    
      public MyFragment() {
    
      }
    
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
    
      }
    
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
                               Bundle savedInstanceState) {
          return inflater.inflate(R.layout.fragment_my,container,false);
      }
    
      @Override
      public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
          super.onViewCreated(view, savedInstanceState);
          FragmentMyBinding binding = FragmentMyBinding.bind(view);
          this.binding = binding;
    
          binding.textView.setText("這是Fragment");
          binding.button.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  Log.d("Fragment", "點擊了按鈕");
              }
          });
      }
    
      @Override
      public void onDestroy() {
          super.onDestroy();
          binding = null;
      }
    
    

    使用View Binding 寫的基類

    1. 通過反射的方式
    //Java
    public class BaseActivity<T extends ViewBinding> extends AppCompatActivity {
      protected T viewBinding;
    
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
          Class cls = (Class) type.getActualTypeArguments()[0];
          try {
              Method inflate = cls.getDeclaredMethod("inflate", LayoutInflater.class);
              viewBinding = (T) inflate.invoke(null, getLayoutInflater());
              setContentView(viewBinding.getRoot());
          } catch (NoSuchMethodException | IllegalAccessException| InvocationTargetException e) {
              e.printStackTrace();
          }
      }
    }
    
    //使用
    
    public class MainActivity extends BaseActivity<ActivityMainBinding> {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            viewBinding.button.setText("這是 MainActivity ViewBinding");
            viewBinding.button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Log.d("MainView","點擊按鈕");
                }
            });
        }
    }
    
    
    
//Kotlin
open class BaseActivity<T : ViewBinding> : AppCompatActivity() {
    protected lateinit var binding: T
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val type = javaClass.genericSuperclass as ParameterizedType
        val aClass = type.actualTypeArguments[0] as Class<*>
        val method = aClass.getDeclaredMethod("inflate", LayoutInflater::class.java)
        binding = method.invoke(null, layoutInflater) as T
        setContentView(binding.root)
    }
}

class MainActivity : BaseActivity<ActivityMainBinding>() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding.textView.text = "這是MainActivity"
    }
}
//Java
public class BaseFragment<T extends ViewBinding> extends Fragment {
    protected T viewBinding;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
        Class cls = (Class) type.getActualTypeArguments()[0];
        try {
            Method inflate = cls.getDeclaredMethod("inflate", LayoutInflater.class, ViewGroup.class, boolean.class);
            viewBinding = (T) inflate.invoke(null, inflater, container, false);
        }  catch (NoSuchMethodException | IllegalAccessException| InvocationTargetException e) {
            e.printStackTrace();
        }
        return viewBinding.getRoot();
    }
}

//使用
public class MainFragment extends BaseFragment<FragmentMainBinding>{
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        viewBinding.button.setText("這是 MainFragment ViewBinding");
        viewBinding.button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d("MainView","點擊按鈕");
            }
        });
    }
}
//Kotlin
open class BaseFragment<T:ViewBinding>:Fragment(){
    lateinit var binding: T
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val type = javaClass.genericSuperclass as ParameterizedType
        val aClass = type.actualTypeArguments[0] as Class<*>
        val method = aClass.getDeclaredMethod("inflate", LayoutInflater::class.java,ViewGroup::class.java,Boolean::class.java)
        binding = method.invoke(null,layoutInflater,container,false) as T
        return binding.root
    }
}

class FirstFragment : BaseFragment<FragmentFirstBinding>() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.textView.text = "這是FirstFragment"
    }
}

2.不通過反射的方式

abstract class BaseActivity<T : ViewBinding> : AppCompatActivity() {
    private lateinit var _binding: T
    protected val binding get() = _binding;

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        _binding = getViewBinding()
        setContentView(_binding.root)
    }

    protected abstract fun getViewBinding(): T
}

class MainActivity : BaseActivity<ActivityMainBinding>() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding.textView.text = "這是MainActivity"
    }

    override fun getViewBinding() = ActivityMainBinding.inflate(layoutInflater)
}
abstract class BaseFragment<T : ViewBinding> : Fragment() {
    private lateinit var _binding: T
    protected val binding get() = _binding;
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = getViewBinding(inflater, container)
        return _binding.root
    }
    
    protected abstract fun getViewBinding(inflater: LayoutInflater, container: ViewGroup?): T
}

class FirstFragment : BaseFragment<FragmentFirstBinding>() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.textView.text = "這是FirstFragment"
    }

    override fun getViewBinding(
        inflater: LayoutInflater,
        container: ViewGroup?
    ) = FragmentFirstBinding.inflate(inflater, container, false)
}
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