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Jetpack ViewBinding

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Jetpack ViewBinding官网文档通过视图绑定功能，您可以更轻松地编写可与视图交互的代码。在模块中启用视图绑定之后，系统会为该模块中的每个XML布局文件生成一个绑定类。绑定类的实例包含对在相应布局中具有ID的所有视图的直接引用。

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文章目录

Jetpack ViewBinding

概述

官网文档

通过视图绑定功能，您可以更轻松地编写可与视图交互的代码。在模块中启用视图绑定之后，系统会为该模块中的每个 XML 布局文件生成一个绑定类。绑定类的实例包含对在相应布局中具有 ID 的所有视图的直接引用。

ViewBinding优点

ViewBinding优点

  • Null 安全：由于视图绑定会创建对视图的直接引用，因此不存在因视图 ID 无效而引发 Null 指针异常的风险。
  • 类型安全：每个绑定类中的字段均具有与它们在 XML 文件中引用的视图相匹配的类型。因此不存强制转换导致的异常风险。

与findViewById区别

  • findViewById编写过于冗余。
  • 类型仍然不安全。

与ButterKnife区别

  • 官宣不维护，推荐使用ViewBinding。
  • 类型仍然不安全。
  • 对组件化项目不友好。

与Kotlin Android Extensions

  • JetBrains废弃该插件。
  • 类型仍然不安全。
  • 性能偏低。

配置ViewBinding

Android Studio3.6以上

android { 
   
    viewBinding { 
   
        enabled = true
    }
}

Android Studio4.0以上

android { 
   
    buildFeatures { 
   
        viewBinding = true
    }
}

如果需要忽略某个布局文件，需要添加tools:viewBindingIgnore="true"属性到布局中

<LinearLayout ... tools:viewBindingIgnore="true" >
  		  ...
</LinearLayout>

使用

当开启ViewBinding后，系统会为该模块中每个XML布局文件生成一个绑定类（转换为驼峰命名并在末尾添加Binding），每个绑定类均包含根视图已交具有id的所有视图的引用。

例如：布局文件名为activity_main.xml，生成绑定类为ActivityMainBinding

在Activity中使用

使用流程

  • 开启视图绑定功能后，系统会为该模块中的XML布局生成一个绑定类，每个绑定类都包含根布局和具有ID布局的引用。
  • 调用绑定类的inflate()方法获取绑定类对象。
  • 调用绑定类对象的getRoot()方法获取根布局传递到setContentView()。

XML布局

activity_view_binding_simple.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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" android:gravity="center_horizontal" android:orientation="vertical">

    <TextView android:id="@+id/tv_name" android:layout_width="wrap_content" android:layout_height="wrap_content" />

    <TextView android:id="@+id/tv_age" android:layout_width="wrap_content" android:layout_height="wrap_content" />

    <ImageView android:id="@+id/iv_avatar" android:layout_width="wrap_content" android:layout_height="wrap_content" />

    <Button android:id="@+id/btn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="确定" />
</LinearLayout>

Activity类

class ViewBindingSimpleActivity : BaseActivity() { 
   
    override fun onCreate(savedInstanceState: Bundle?) { 
   
        super.onCreate(savedInstanceState)
        val viewBinding = ActivityViewBindingSimpleBinding.inflate(layoutInflater)
        setContentView(viewBinding.root)

        viewBinding.tvName.text = "hello world"
        viewBinding.tvAge.text = 18.toString()
        viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        viewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()
        }
    }
}

在Fragment中使用

方式一

  • 调用绑定类的inflate()方法，获取绑定类对象。
  • 再调用getRoot()方法获取根布局。
  • 在onCreateView()方法返回根布局，使其成为屏幕上的活动视图。
  • 由于Fragment的存在时间比视图长。因此需要在Fragment的onDestroyView()方法中清除对绑定类对象的所有引用。
class MyFragment : BaseFragment() { 
   
    private var _viewBinding: FragmentMyBinding? = null
    private val viewBinding
    	get() = _viewBinding!!

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View { 
   
        _viewBinding = FragmentMyBinding.inflate(inflater, container, false)
        return viewBinding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
   
        super.onViewCreated(view, savedInstanceState)
        viewBinding.tvName.text = "hello world"
        viewBinding.tvAge.text = 18.toString()
        viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        viewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()
        }
    }

    override fun onDestroyView() { 
   
        super.onDestroyView()
        _viewBinding = null
    }
}

方式二

class MyFragment : BaseFragment() { 
   
    private var _viewBinding: FragmentMyBinding? = null
    private val viewBinding
        get() = _viewBinding!!

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View { 
   
        return inflater.inflate(R.layout.fragment_my, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
   
        super.onViewCreated(view, savedInstanceState)
        _viewBinding = FragmentMyBinding.bind(view)
        viewBinding.tvName.text = "hello world"
        viewBinding.tvAge.text = 18.toString()
        viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        viewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()
        }
    }

    override fun onDestroyView() { 
   
        super.onDestroyView()
        _viewBinding = null
    }
}

在RecyclerView adapter中使用

class MyAdapter(context: Context, private val data: ArrayList<String>) :
	RecyclerView.Adapter<MyAdapter.ViewHolder>() { 
   
    val layoutInflater: LayoutInflater = LayoutInflater.from(context)

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) { 
   
        val text: TextView = itemView.findViewById(R.id.text)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder { 
   
        val viewBinding = ItemTextBinding.inflate(layoutInflater, parent, false)
        return ViewHolder(viewBinding.root)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) { 
   
        holder.text.text = data[position]
    }

    override fun getItemCount(): Int { 
   
        return data.size
    }
}

在include标签中使用

ViewBinding可以与<include>标签一起使用

不使用merge标签

  • 一定要给<include>标签定义id，使用该id访问布局中的控件。

XML布局

title_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:background="#2196F3" android:minHeight="50dp" android:padding="10dp">

    <TextView android:id="@+id/back" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerVertical="true" android:text="返回" />

    <TextView android:id="@+id/title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="标题位置" />

    <TextView android:id="@+id/confirm" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentRight="true" android:layout_centerVertical="true" android:text="确定" />

</RelativeLayout>

Activity的XML布局

activity_vbinclude.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".IncludeActivity">

    <include android:id="@+id/titleBar" layout="@layout/titlebar" />

</LinearLayout>

在include标签中使用

public class IncludeActivity extends AppCompatActivity { 
   
    private Context context;

    @Override
    protected void onCreate(Bundle savedInstanceState) { 
   
        super.onCreate(savedInstanceState);
        context = this;
        ActivityIncludeBinding binding = ActivityIncludeBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        binding.titleBar.title.setText("这是一个标题");
        binding.titleBar.back.setOnClickListener(new View.OnClickListener() { 
   
            @Override
            public void onClick(View v) { 
   
                Toast.makeText(context, "返回", Toast.LENGTH_SHORT).show();
            }
        });
        binding.titleBar.confirm.setOnClickListener(new View.OnClickListener() { 
   
            @Override
            public void onClick(View v) { 
   
                Toast.makeText(context, "确定", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

使用merge标签

  • <merge>标签有利于减少布局层次。
  • 需要使用bind()方法绑定根视图。
  • 不能给<include>标签设置id。

布局：detail_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <ImageView android:id="@+id/ivDetail" android:layout_width="100dp" android:layout_height="100dp" android:scaleType="fitXY" />
</merge>

Activity的XML布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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" android:orientation="vertical" tools:context=".IncludeActivity">

    <include layout="@layout/detail_layout" />

</LinearLayout>

在include标签中使用

package com.example.viewbindingdemo;

import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import com.example.viewbindingdemo.databinding.ActivityIncludeBinding;
import com.example.viewbindingdemo.databinding.DetailLayoutBinding;

public class IncludeActivity extends AppCompatActivity { 
   

    private Context context;

    @Override
    protected void onCreate(Bundle savedInstanceState) { 
   
        super.onCreate(savedInstanceState);
        context = this;
        ActivityIncludeBinding binding = ActivityIncludeBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        DetailLayoutBinding detailBinding = DetailLayoutBinding.bind(binding.getRoot());
        detailBinding.ivDetail.setImageResource(R.mipmap.ic_launcher);
    }
}

封装使用

基类封装，不使用反射

基类封装

abstract class BindingActivity<VB : ViewBinding> : BaseActivity() { 
   
    private lateinit var _viewBinding: VB
    protected val mViewBinding get() = _viewBinding

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

    abstract fun getViewBinding(): VB
}

abstract class BindingFragment<VB : ViewBinding> : BaseFragment() { 
   
    private lateinit var _viewBinding: VB
    protected val mViewBinding get() = _viewBinding

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? { 
   
        _viewBinding = getViewBinding(inflater, container)
        return _viewBinding.root
    }

    abstract fun getViewBinding(inflater: LayoutInflater, container: ViewGroup?): VB
}

使用

class OneActivity : BindingActivity<ActivityOneBinding>() { 
    

    override fun onCreate(savedInstanceState: Bundle?) { 
   
        super.onCreate(savedInstanceState)
        mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        mViewBinding.tvName.text = "小白"
        mViewBinding.tvAge.text = 18.toString()
        mViewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()
        }
    }

    override fun getViewBinding(): ActivityOneBinding { 
   
        return ActivityOneBinding.inflate(layoutInflater)
    }
}

class OneFragment : BindingFragment<FragmentOneBinding>() { 
   
    override fun getViewBinding(
        inflater: LayoutInflater,
        container: ViewGroup?
    ): FragmentOneBinding { 
   
        return FragmentOneBinding.inflate(inflater, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
   
        super.onViewCreated(view, savedInstanceState)
        mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        mViewBinding.tvName.text = "小白"
        mViewBinding.tvAge.text = 18.toString()
        mViewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello", Toast.LENGTH_SHORT).show()
        }
    }
}

基类封装，使用反射

基类封装

abstract class BindingActivity<VB : ViewBinding> : BaseActivity() { 
   
    private lateinit var _viewBinding: VB
    protected val mViewBinding get() = _viewBinding

    override fun onCreate(savedInstanceState: Bundle?) { 
   
        super.onCreate(savedInstanceState)
        mContext = this
        val type = javaClass.genericSuperclass
        if (type is ParameterizedType) { 
   
            val clz = type.actualTypeArguments[0] as Class<*>
            val method = clz.getMethod("inflate", LayoutInflater::class.java)
            _viewBinding = method.invoke(null, layoutInflater) as VB
            setContentView(_viewBinding.root)
        }
    }
}

abstract class BindingFragment<VB : ViewBinding> : BaseFragment() { 
   
    private var _viewBinding: VB? = null
    protected val mViewBinding get() = _viewBinding!!

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View { 
   
        val type = javaClass.genericSuperclass
        if (type is ParameterizedType) { 
   
            val clz = type.actualTypeArguments[0] as Class<*>
            val method = clz.getMethod(
                "inflate", LayoutInflater::class.java, ViewGroup::class.java, Boolean::class.java
            )
            _viewBinding = method.invoke(null, inflater, container, false) as VB
        }
        return mViewBinding.root
    }

    override fun onDestroyView() { 
   
        super.onDestroyView()
        _viewBinding = null
    }
}

使用

class TwoActivity : BindingActivity<ActivityTwoBinding>() { 
   
    override fun onCreate(savedInstanceState: Bundle?) { 
   
        super.onCreate(savedInstanceState)
        mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        mViewBinding.tvName.text = "小白"
        mViewBinding.tvAge.text = 28.toString()
        mViewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello2", Toast.LENGTH_SHORT).show()
        }
    }
}

class TwoFragment : BindingFragment<FragmentTwoBinding>() { 
   
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
   
        super.onViewCreated(view, savedInstanceState)
        mViewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        mViewBinding.tvName.text = "小白"
        mViewBinding.tvAge.text = 28.toString()
        mViewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello2", Toast.LENGTH_SHORT).show()
        }
    }
}

委托实现

封装

//Activity ViewBinding

inline fun <reified VB : ViewBinding> ComponentActivity.viewBindings(
    noinline factory: (LayoutInflater) -> VB,
    setContentView: Boolean = true
) = ActivityViewBindingDelegate1(factory, setContentView)

inline fun <reified VB : ViewBinding> ComponentActivity.viewBindings(setContentView: Boolean = true) =
    ActivityViewBindingDelegate2(VB::class.java, setContentView)

class ActivityViewBindingDelegate1<VB : ViewBinding>(
    private val factory: (LayoutInflater) -> VB,
    private val setContentView: Boolean,
) : ReadOnlyProperty<ComponentActivity, VB> { 
   
    private var viewBinding: VB? = null

    override fun getValue(thisRef: ComponentActivity, property: KProperty<*>): VB { 
   
        viewBinding?.let { 
    return it }

        viewBinding = factory(thisRef.layoutInflater).also { 
    viewBinding ->
            if (setContentView) thisRef.setContentView(viewBinding.root)
        }
        return viewBinding!!
    }
}

class ActivityViewBindingDelegate2<VB : ViewBinding>(
    private val clazz: Class<VB>,
    private val setContentView: Boolean,
) : ReadOnlyProperty<ComponentActivity, VB> { 
   
    private var viewBinding: VB? = null

    override fun getValue(thisRef: ComponentActivity, property: KProperty<*>): VB { 
   
        viewBinding?.let { 
    return it }

        val inflateMethod = clazz.getMethod("inflate", LayoutInflater::class.java)
        viewBinding =
            (inflateMethod.invoke(null, thisRef.layoutInflater) as VB).also { 
    viewBinding ->
                if (setContentView) thisRef.setContentView(viewBinding.root)
            }
        return viewBinding!!
    }
}

//Fragment ViewBinding

inline fun <reified VB : ViewBinding> Fragment.viewBindings(noinline factory: (View) -> VB) =
    FragmentViewBindingDelegate1(factory)

inline fun <reified VB : ViewBinding> Fragment.viewBindings() =
    FragmentViewBindingDelegate2(VB::class.java)

class FragmentViewBindingDelegate1<VB : ViewBinding>(
    private val factory: (View) -> VB,
) : ReadOnlyProperty<Fragment, VB> { 
   
    private var viewBinding: VB? = null

    override fun getValue(thisRef: Fragment, property: KProperty<*>): VB { 
   
        viewBinding?.let { 
    return it }

        val lifecycle = thisRef.viewLifecycleOwner.lifecycle
        viewBinding = factory(thisRef.requireView())
        if (lifecycle.currentState == Lifecycle.State.DESTROYED) { 
   
            Log.w(
                "TAG",
                "Access to viewBinding after Lifecycle is destroyed or hasn't created yet. The instance of viewBinding will be not cached."
            )
        } else { 
   
            thisRef.viewLifecycleOwnerLiveData.observe(thisRef) { 
    viewLifecycleOwner ->
                viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver { 
   
                    override fun onDestroy(owner: LifecycleOwner) { 
   
                        viewBinding = null
                    }
                })
            }
        }

        return viewBinding!!
    }
}

class FragmentViewBindingDelegate2<VB : ViewBinding>(
    clazz: Class<VB>,
) : ReadOnlyProperty<Fragment, VB> { 
   
    private var viewBinding: VB? = null

    private val bindMethod = clazz.getMethod("bind", View::class.java)

    override fun getValue(thisRef: Fragment, property: KProperty<*>): VB { 
   
        viewBinding?.let { 
    return it }

        val lifecycle = thisRef.viewLifecycleOwner.lifecycle
        viewBinding = bindMethod.invoke(null, thisRef.requireView()) as VB
        if (lifecycle.currentState == Lifecycle.State.DESTROYED) { 
   
            Log.w(
                "TAG",
                "Access to viewBinding after Lifecycle is destroyed or hasn't created yet. The instance of viewBinding will be not cached."
            )
        } else { 
   
            thisRef.viewLifecycleOwnerLiveData.observe(thisRef) { 
    viewLifecycleOwner ->
                viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver { 
   
                    override fun onDestroy(owner: LifecycleOwner) { 
   
                        viewBinding = null
                    }
                })
            }
        }

        return viewBinding!!
    }
}

使用

class ThreeActivity : BaseActivity() { 
   
    //方式一
    private val viewBinding: ActivityThreeBinding by viewBindings(ActivityThreeBinding::inflate)
    //方式二
    // private val viewBinding: ActivityThreeBinding by viewBindings()

    override fun onCreate(savedInstanceState: Bundle?) { 
   
        super.onCreate(savedInstanceState)
        viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        viewBinding.tvName.text = "小白"
        viewBinding.tvAge.text = 38.toString()
        viewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello3", Toast.LENGTH_SHORT).show()
        }
    }
}

class ThreeFragment : BaseFragment(R.layout.fragment_three) { 
   
    //方式一
// private val viewBinding: FragmentThreeBinding by viewBindings(FragmentThreeBinding::bind)
    //方式二
    private val viewBinding: FragmentThreeBinding by viewBindings()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) { 
   
        super.onViewCreated(view, savedInstanceState)
        viewBinding.ivAvatar.setImageResource(R.mipmap.ic_launcher_round)
        viewBinding.tvName.text = "小白33"
        viewBinding.tvAge.text = 338.toString()
        viewBinding.btn.setOnClickListener { 
   
            Toast.makeText(mContext, "hello33", Toast.LENGTH_SHORT).show()
        }
    }
}

源码分析

代码下载

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