JetPack Databinding使用

imageview绑定databinding的用法

//新建工具类
    @BindingAdapter("bind:studentAvatar")
    public static void showImageByUrl(final ImageView imageView, String url) {
//     imageView.setImageResource(resId);
       Glide.with(imageView).load(url).into(imageView);
    }

       //布局使用
        <ImageView
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:layout_marginRight="10dp"
            android:layout_marginLeft="10dp"
            app:studentAvatar="@{@string/image_url}"/>

一、什么是ViewBinding

View Binding是Android Studio 3.6推出的新特性，旨在替代findViewById(内部实现还是使用findViewById)。通过ViewBinding，可以更轻松地编写可与视图交互的代码。在模块中启用ViewBinding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。

在大多数情况下，视图绑定会替代 findViewById

注意：视图绑定在 Android Studio 3.6 Canary 11 及更高版本中可用

二、ViewBinding怎么使用

启用Viewbinding
在模块build.gradle文件android节点下添加如下代码

**

android {
      
    viewBinding{
        enabled = true
    }
}

在 Android Studio 4.0 中，viewBinding 变成属性被整合到了 buildFeatures 选项中，所以配置要改成:

**

// Android Studio 4.0
android {
 buildFeatures {
  viewBinding = true
 }
}

重新编译后系统会为每个布局文件生成对应的Binding类，该类中包含对应布局中具有 ID 的所有视图的直接引用。生成类的目录在 模块根目录/build/generated/data_binding_base_class_source_out下。

在Activity中使用

**

// 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">

    <TextView
        android:id="@+id/tv_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>

**

ActivityMainBinding mViewBinding;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mViewBinding = ActivityMainBinding.inflate(getLayoutInflater());
    setContentView(mViewBinding.getRoot());
    ...
}

kotlin:

**

package androidstack.viewbinding

import android.os.Bundle
import androidstack.viewbinding.databinding.ActivityMainBinding
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //获取绑定类实例
        binding = ActivityMainBinding.inflate(layoutInflater)
        //通过绑定类获取布局后，传给setContentView设置内容视图
        setContentView(binding.root)
        //通过绑定类获取对应的ID视图，进行操作
        binding.tvHelloWorld.text = "视图绑定"
    }
}

Binding文件名和布局中控件根据驼峰命名规则生成；
使用的时候在Activity的onCreate方法里调用其静态inflate方法，返回ViewBinding实例，通过ViewBinding实例可以直接访问布局文件中带id的控件，比如上面的TextView， mViewBinding.tvTextView
如果想在生成绑定类时忽略某个布局文件，将 tools:viewBindingIgnore="true"属性添加到相应布局文件的根视图中。

使用View Binding 写的基类

**

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 = "这是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 = "这是FirstFragment"
    }

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

Fragment中使用

**

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("这是Fragment");
      binding.button.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              Log.d("Fragment", "点击了按钮");
          }
      });
  }

  @Override
  public void onDestroy() {
      super.onDestroy();
      binding = null;
  }

在Dialog中的使用

**

class MyDialog extends Dialog {
    protected View mView;
    protected MyDialogBinding mBinding;

    public MyDialog(@NonNull Context context) {
        super(context,R.style.Dialog);
        mBinding = MyDialogBinding.inflate(getLayoutInflater());
        mView = mBinding.getRoot();

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(mView);
        Window window = this.getWindow();
        WindowManager.LayoutParams lp = window.getAttributes();
        Display d = window.getWindowManager().getDefaultDisplay();
        lp.width = (int) (d.getWidth() * 0.9F);
        window.setAttributes(lp);
    }
  

}

在 Adapter 中的使用

**

public class MainAdapter extends RecyclerView.Adapter<MainAdapter.ViewHolder> {

    private List<String> mList;

    public MainAdapter(List<String> list) {
        mList = list;
    }

    @NonNull
    @Override
    public MainAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //之前的写法
        //View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_comment, parent, false);
        //ViewHolder holder = new ViewHolder(view);

        //使用ViewBinding的写法
        LayoutCommentBinding commentBinding = LayoutCommentBinding.inflate(LayoutInflater.from(parent.getContext()), parent, false);
        ViewHolder holder = new ViewHolder(commentBinding);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull MainAdapter.ViewHolder holder, int position) {
        holder.mTextView.setText(mList.get(position));
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }

    static class ViewHolder extends RecyclerView.ViewHolder {

        TextView mTextView;

        //之前的写法
        //public ViewHolder(@NonNull View itemView) {
        //    super(itemView);
        //    mTextView = itemView.findViewById(R.id.tv_include);
        //}

        //使用ViewBinding的写法
        ViewHolder(@NonNull LayoutCommentBinding commentBinding) {
            super(commentBinding.getRoot());
            mTextView = commentBinding.tvInclude;
        }

    }
}

自定义View中使用

如果我们的自定义View中使用了layout布局，比如layout_my_view.xml，如下

**

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="这是自定义布局"
        android:textSize="50sp" />

</androidx.constraintlayout.widget.ConstraintLayout>

会生成一个名为LayoutMyViewViewBinding.java文件，在自定义View通过如下方式绑定，

**

public class MyView extends View {
    public MyView (Context context) {
        this(context, null);
    }

    public MyView (Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MyView (Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        LayoutMyViewViewBinding viewBinding = LayoutMyViewViewBinding.inflate(LayoutInflater.from(getContext()), this, true);
    }
}

如果自定义View布局文件中使用merge标签，

**

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

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="这是自定义merge"
        android:textSize="50sp" />

</merge>

此时要写成下面这个样子，

**

LayoutMyViewViewBinding viewBinding = LayoutMyViewViewBinding.inflate(LayoutInflater.from(context), this);

include 标签的使用

include 标签不带 merge 标签，需要给 include 标签添加 id, 直接使用 id 即可，用法如下所示。

**

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

ActivityMainBinding binding = ActivityMainBinding.inflate(layoutInflater);
binding.include.includeTvTitle.setText("使用 include 布局中的控件, 不包含 merge");

include 标签带 merge 标签，需要通过bind()将merge布局绑定到主布局上，用法如下所示。

**

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

ActivityMainBinding binding = ActivityMainBinding.inflate(layoutInflater);
LayoutMergeItemBinding mergeItemBinding = LayoutMergeItemBinding.bind(binding.getRoot())；
mergeItemBinding.mergeTvTitle.setText("使用 include 布局中的控件, 包含 merge");

三、原理

原理就是Google在那个用来编译的gradle插件中增加了新功能，当某个module开启ViewBinding功能后，编译的时候就去扫描此模块下的layout文件，生成对应的binding类。

**

public final class ActivityMainBinding implements ViewBinding {
    @NonNull
    private final ConstraintLayout rootView;

    @NonNull
    public final TextView tvTextView;

    private ActivityMainBinding(@NonNull ConstraintLayout rootView,
                                            @NonNull TextView rvDataList) {
        this.rootView = rootView;
        this.tvTextView = tvTextView;
    }

    @Override
    @NonNull
    public ConstraintLayout getRoot() {
        return rootView;
    }

    @NonNull
    public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater) {
        return inflate(inflater, null, false);
    }

    @NonNull
    public static ActivityMainBinding inflate(@NonNull LayoutInflater inflater,
                                                          @Nullable ViewGroup parent, boolean attachToParent) {
        View root = inflater.inflate(R.layout.activity_main, parent, false);
        if (attachToParent) {
            parent.addView(root);
        }
        return bind(root);
    }

    @NonNull
    public static ActivityMainBinding 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.
        String missingId;
        missingId:
        {
            TextView tvTextView = rootView.findViewById(R.id.tv_text);
            if (tvTextView == null) {
                missingId = "tvTextView";
                break missingId;
            }
            return new ActivityMainBinding((ConstraintLayout) rootView, tvTextView);
        }
        throw new NullPointerException("Missing required view with ID: ".concat(missingId));
    }
}

可以看出，最终使用的仍然是findViewById，和ButterKnife异曲同工，不同的是ButterKnife通过编译时注解生成ViewBinding类，而ViewBinding是通过编译时扫描layout文件生成ViewBinding类。

四、与findViewById相比优点

与使用 findViewById 相比，视图绑定具有一些很显著的优点：

• 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。此外，如果视图仅出现在布局的某些配置中（比如横竖屏布局内容差异），则绑定类中包含其引用的字段会使用 @Nullable 标记。

• 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。这意味着不存在发生类转换异常的风险。
  这些差异意味着布局和代码之间的不兼容将会导致构建在编译时（而非运行时）失败。

参考二

目前，谷歌在 Android Studio 3.6 Canary 11 及更高版本中加入了新的视图绑定方式ViewBinding。 注意：要使用ViewBinding功能，AndroidStudio至少要升级到3.6。

使用方法 在要使用ViewBinding的 module 的build.gradle文件中开启ViewBinding

android {
    ……………
    viewBinding {
        enabled = true
    }
    ……………
}

如果在使用的过程中不想为某个布局文件生成binding类，则可以使用如下属性添加到布局的根视图中：

<androidx.constraintlayout.widget.ConstraintLayout
  …………
      tools:viewBindingIgnore="true" >
  …………
</androidx.constraintlayout.widget.ConstraintLayout>

在gradle文件中开启ViewBinding功能后,编译器就会为此模块下的每个布局文件都产生一个对应的绑定类。 这个绑定类是我们的布局名称去掉下划线使用驼峰的形式结尾接Binding； 例如： activity_gender_guide.xml 就是： ActivityGenderGuideBinding

使用viewbinding后，不需要再findViewById找控件， 直接通过binding.控件Id名称就可以，控件id名称也是去掉下滑线使用驼峰的形式。 viewbinding的inflate有两种方法，根据直接所需选择 1：inflate(getLayoutInflater()); 2：inflate(inflater, container, false);

在Activity里使用

public class GenderGuideActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //之前的写法
        setContentView(R.layout.activity_gender_guide);
        TextView guide_title = (TextView) findViewById(R.id.guide_title);
        guide_title.setText("标题");
        
        //使用viewbinding的写法
        ActivityGenderGuideBinding binding = ActivityGenderGuideBinding.inflate(getLayoutInflater());
		setContentView(binding.getRoot());
		binding.guideTitle.setText("标题");
     }

在Fragment里使用

public class ReadingHistoryFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    	//以前的写法
    	View view = inflater.inflate(R.layout.list_with_empty_view, null);
    	TextView empty_text = (TextView) view.findViewById(R.id.empty_text);
    	empty_text.setText("标题");
    	return view;
    	//使用viewbinding的写法
        ListWithEmptyViewBinding binding = ListWithEmptyViewBinding.inflate(inflater, container, false);
        binding.emptyText.setText("标题");
        return binding.getRoot();
    }

}

在BaseAdapter里使用 以前的写法

public class ListAdapter extends BaseAdapter {
    private Activity activity;
    private List<String> list;

    public ListAdapter(Activity activity, List<String> list) {
        this.activity = activity;
        this.list = list;
    }

    @Override
    public int getCount() {
        return list == null ? 0 : list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    class ViewHolder {
        ImageView iv_cover;
        TextView tv_bookname;
        TextView tv_author;
        TextView tv_url_or_chapter;
        TextView tv_archive_date;
        ImageView iv_popup_hint;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            convertView = LayoutInflater.from(activity).inflate(R.layout.archive_list_item, null);
            holder = new ViewHolder();
            holder.iv_cover = (ImageView) convertView.findViewById(R.id.iv_cover);
            holder.tv_bookname = (TextView) convertView.findViewById(R.id.tv_bookname);
            holder.tv_author = (TextView) convertView.findViewById(R.id.tv_author);
            holder.tv_url_or_chapter = (TextView) convertView.findViewById(R.id.tv_url_or_chapter);
            holder.tv_archive_date = (TextView) convertView.findViewById(R.id.tv_archive_date);
            holder.iv_popup_hint = (ImageView) convertView.findViewById(R.id.iv_popup_hint);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        return convertView;
    }
    }

使用viewbinding的写法

public class ListAdapter extends BaseAdapter {
    private Activity activity;
    private List<String> list;

    public ListAdapter(Activity activity, List<String> list) {
        this.activity = activity;
        this.list = list;
    }

    @Override
    public int getCount() {
        return list == null ? 0 : list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ArchiveListItemBinding binding; 
        if (convertView == null) {
            binding = ArchiveListItemBinding.inflate(activity.getLayoutInflater(), null, false);
            convertView = binding.getRoot();
            convertView.setTag(binding);
        } else {
            binding = (ArchiveListItemBinding) convertView.getTag();
        }
        binding.tvBookname.setText("标题");
        return convertView;
    }
    }

在RecyclerView结合Adapter使用

public class MainAdapter extends RecyclerView.Adapter<MainAdapter.ViewHolder> {

    private List<String> mList;

    public MainAdapter(List<String> list) {
        mList = list;
    }

    @NonNull
    @Override
    public MainAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //之前的写法
        //View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_comment_item, parent, false);
        //ViewHolder holder = new ViewHolder(view);

        //使用ViewBinding的写法
        LayoutCommentItemBinding commentItemBinding = LayoutCommentItemBinding.inflate(LayoutInflater.from(parent.getContext()), parent, false);
        ViewHolder holder = new ViewHolder(commentBinding);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull MainAdapter.ViewHolder holder, int position) {
        holder.mTextView.setText("标题");
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        TextView mTextView;
        //之前的写法
        //public ViewHolder(@NonNull View itemView) {
        //    super(itemView);
        //    mTextView = itemView.findViewById(R.id.tv_name);
        //}

        //使用ViewBinding的写法
        ViewHolder(@NonNull LayoutCommentItemBinding commentItemBinding) {
            super(commentItemBinding.getRoot());
            mTextView = commentItemBinding.tvName;
        }

    }
}

自定义Dialog的使用

	public static void showRechargeAlertDialog(Context context, String title, int type, final OnSingleChoiceSelectedListener singleChoiceSelectedListener){
		//之前的写法
		View view = View.inflate(context, R.layout.dialog_recharge, null);
		TextView dialog_title = view.findViewById(R.id.dialog_title);
		dialog_title.setText("标题");
		final AlertDialog alertDialog = createAlertDialog(context, view, true);
		//使用viewbinding的写法
		DialogRechargeBinding binding = DialogRechargeBinding.inflate(LayoutInflater.from(context));
        binding.dialogTitle.setText("标题");
        final AlertDialog alertDialog = createAlertDialog(context, binding.getRoot(), true);
	}
	//创建共用的dialog的属性
    public static AlertDialog createAlertDialog(Context context, View view, boolean isCancelable){
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setView(view);
        final AlertDialog catDialog = builder.show();
        catDialog.setCancelable(isCancelable);//按返回键是否可以退出，true允许
        catDialog.getWindow().setBackgroundDrawable(null);
        catDialog.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_VISIBLE);
        WindowManager.LayoutParams lp = catDialog.getWindow().getAttributes();
        lp.width = SystemUtil.getScreenWidth(context); //设置宽度
        lp.height = WindowManager.LayoutParams.WRAP_CONTENT;
        catDialog.getWindow().setAttributes(lp);
        return catDialog;
    }

Popupwindow也是一样就不重复了。

使用的layout文件有include

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_money_income);
        ActivityMoneyIncomeBinding moneyIncomeBinding = ActivityMoneyIncomeBinding.bind(getContainer());;
		//如果include的布局是当前 module里的布局
		//就可以直接调用
		//moneyIncomeBinding.moneyView.title.setText("标题");
		//如果是其它module里的
		//那么需要在哪个module里开启viewbinding
		//调用方法
        View money_view = findViewById(R.id.money_view);
        MartianMoneyWithdrawViewBinding moneyBinding = MartianMoneyWithdrawViewBinding.bind(money_view);
		moneyBinding.title.setText("标题");
}