DataBinding

• Google文档 https://developer.android.google.cn/topic/libraries/data-binding

• 项目涉及代码库 https://gitee.com/pengqinping/architecture-components-samples/tree/master/BasicSample

• dataBinding https://gitee.com/pengqinping/databinding-samples

databinding 相对比较简单

1. app 开启 dataBinding 支持 buidle.gradle

android {
    dataBinding {
        enabled = true
    }
}

2. 定义xml文件支持dataBinding 以list_fragment.xml 为例

<!-- 关键是layout 包裹，只有Layout包裹 DataBinding才会去识别 -->
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>
        <variable
            name="isLoading"
            type="boolean" />
    </data>
<!-- ...  somecode -->

<androidx.appcompat.widget.AppCompatEditText
        android:id="@+id/products_search_box"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:hint="@string/search_products_hint"/>

    <ImageButton
        android:id="@+id/products_search_btn"
        android:layout_width="48dp"
        android:layout_height="48dp"
        android:contentDescription="@string/cd_search_products"
        app:srcCompat="@drawable/ic_search_black_24dp"/>
<!-- ...  somecode -->
</layout>

3. dataBinding 工具会在编译的时候 ListFragmentBinding.java 文件 里面有描述 布局的代码

目录 app/buidl/generated/data_binding_base_class_source_out/{debug}/out/{packagname}/databinding/xxx.java

//列举一小部分
public abstract class ListFragmentBinding extends ViewDataBinding {
@NonNull
public final AppCompatEditText productsSearchBox;

@NonNull
public final ImageButton productsSearchBtn;
// ... some code

4. 在 fragment 实例化对象 , 并且使用

private ListFragmentBinding mBinding;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
        @Nullable Bundle savedInstanceState) {
    mBinding = DataBindingUtil.inflate(inflater, R.layout.list_fragment, container, false);
    //... some code
    return mBinding.getRoot();
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    // 通过 binding 对象直接引用
    mBinding.productsSearchBtn.setOnClickListener(v -> {
        Editable query = mBinding.productsSearchBox.getText();
        viewModel.setQuery(query);
    });
}

在布局里面写Viewmodel就不多介绍了，写过 vue angularjs 前端的 这些很好理解， 数据绑定的概念

BaseObservableField 和 ViewModel 在 数据绑定中的引用

• 项目地址 https://gitee.com/pengqinping/databinding-samples/tree/master

1. 用ObservableInt演示

• a.在Activity定义 ObservableInt

  data class ObservableFieldProfile(
      val name: String,
      val lastName: String,
      val likes: ObservableInt
  )
  private val observableFieldProfile = ObservableFieldProfile("Ada", "Lovelace", ObservableInt(0))

• b.在布局定义引用

  <layout
  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">
  <data>
  
      <import type="com.example.android.databinding.basicsample.R"/>
      <import type="com.example.android.databinding.basicsample.util.ConverterUtil"/>
      <!-- 定义名词和类型 -->
      <variable
          name="user"
          type="com.example.android.databinding.basicsample.data.ObservableFieldProfile" />
      <!-- 设置文本 -->
      <xml
          android:text="@{user.name}" />
      <!-- 设置表达式 -->
      <xml 
          app:srcCompat="@{user.likes &lt; 4 ? R.drawable.ic_person_black_96dp : R.drawable.ic_whatshot_black_96dp }"/>
      <!-- 类型转换 -->
      <xml 
          android:text="@{Integer.toString(user.likes)}"
      />
      <!-- 会自动调用 Activity 中的 fun OnLink 函数，Google 不推荐这么干，所以最好使用ViewModel -->
      <button android:onClick="onLike" />
  </data>

• C. 绑定及赋值

  val binding: ObservableFieldProfileBinding =
              DataBindingUtil.setContentView(this, R.layout.observable_field_profile)
      binding.user = observableFieldProfile

1.这个BaseObservableField只适合简单逻辑，加入判断比较复杂就很难受了 2.普通的BaseObservableFiled 对象改变值是需要手动去set更新的

2. ViewModel+LiveData演示

看了ViewModel 你可能会喜欢上使用这个东西

• a. 定义ViewModel 和 LiveData演示

  class ProfileLiveDataViewModel : ViewModel() {
      private val _name = MutableLiveData("Ada") // LiveData ，数据发生变化会自动更新布局，不用在重新拿View 去set数据
      private val _lastName = MutableLiveData("Lovelace")
      private val _likes =  MutableLiveData(0)
  
      // 这里转了一次，主要是避免 在其他地方操作 这边变量，对外自提供 可读操作，内部实现可写操作
      val name: LiveData<String> = _name
      val lastName: LiveData<String> = _lastName
      val likes: LiveData<Int> = _likes
  
      // popularity is exposed as LiveData using a Transformation instead of a @Bindable property.
      // 数据转换
      val popularity: LiveData<Popularity> = Transformations.map(_likes) {
          when {
              it > 9 -> Popularity.STAR
              it > 4 -> Popularity.POPULAR
              else -> Popularity.NORMAL
          }
      }
  
      // xml 中 函数调用
      fun onLike() {
          _likes.value = (_likes.value ?: 0) + 1
      }
  }

• b. 在布局中引入ViewModel

  <data>
      <variable
          name="viewmodel"
          type="com.example.android.databinding.basicsample.data.ProfileLiveDataViewModel"/>
  </data>
  <!-- 变量 -->
  <xml  android:text="@{viewmodel.lastName}"/>
  <!-- 事件 -->
  <xml android:onClick="@{() -> viewmodel.onLike()}"/>

• c. 在Activity中绑定

  // Obtain binding
  val binding: ViewmodelProfileBinding =
          DataBindingUtil.setContentView(this, R.layout.viewmodel_profile)
  
  // Bind layout with ViewModel
  binding.viewmodel = viewModel
  
  // LiveData needs the lifecycle owner
  binding.lifecycleOwner = this

官方还介绍了一种 替换LiveData 方式， @Bindable

• https://developer.android.google.cn/topic/libraries/data-binding/observability