Data Binding

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Data Binding Library

数据绑定库编写声明式布局，尽量减少绑定应用程序逻辑和布局所需的代码，减少布局绑定相关代码

  • build environment

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    android{
    ...
         dataBinding {
            enabled = true
         }
    }

  • Data Binding Compiler V2

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    android.databinding.enableV2=true
    向后不兼容

  • Data Binding 布局文件

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

        <data>

            <import type="java.util.List" />

            <import type="android.view.View" />

            <import type="com.willkernel.www.databindingdemo.User" />

            <import type="com.willkernel.www.databindingdemo.DoSomething" />

            <!--<variable-->
            <!--name="view"-->
            <!--type="View" />-->

            <variable
                name="user"
                type="User" />

            <variable
                name="userClick"
                type="com.willkernel.www.databindingdemo.MainActivity.UserClick" />

            <variable
                name="ds"
                type="DoSomething" />

        </data>

        <android.support.v4.widget.NestedScrollView
            android:layout_width="match_parent"
            android:layout_height="match_parent">


            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical">

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:onClick="@{userClick::onUserClick}"
                    android:text="@{user.firstName}" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:onClick="@{() -> userClick.onUserClick(user)}"
                    android:text="@{user.firstName}" />
                <!--android:onClick="@{userClick::onUserClick}"-->
                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:onClick="@{(v) -> userClick.onUserClick(v,user)}"
                    android:text="@{user.firstName}" />

                <CheckBox
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:onCheckedChanged="@{(cb,isChecked) -> userClick.onCheckedChanged(user,isChecked)}"
                    android:text="@{user.lastName}" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:onLongClick="@{(v)->userClick.onLongClick(v,user)}"
                    android:text="@{user.lastName}" />

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@{user.firstName}"
                    android:visibility="@{user.isAdult ? View.VISIBLE:View.INVISIBLE}" />

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@{DoSomething.capital(user.firstName)}" />
            </LinearLayout>
        </android.support.v4.widget.NestedScrollView>
    </layout>

    • data标签下的variable描述将会在布局中使用的属性

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      <variable name="user" type="com.example.User"/>

    • 使用”@{}” 语法获取属性

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      <TextView android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="@{user.firstName}"/>

    • 三种情况databinding都可以获取属性

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      1. public final String firstName;

      2. private final String firstName;
         public String getFirstName() {
            return this.firstName;
         }
      3. private final String firstName;
         public String firstName() {
            return this.firstName;
         }

  • 数据绑定,默认基于布局文件名称生成绑定类，将其转换为Pascal实例并添加Binding后缀，例如布局文件activity_main.xml,生成的类为MainActivityBinding,持有布局所有属性的绑定方法

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     @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            User user = new User();
            user.firstName = "firstName";
            user.lastName = "lastName";
            user.isAdult = true;
            binding.setUser(user);
            binding.setUserClick(new UserClick());
    }


    也可以这样获取View
    ActivityMainBinding binding =ActivityMainBinding.inflate(getLayoutInflater());
    MyLayoutBinding binding = MyLayoutBinding.inflate(layoutInflater, viewGroup, false);

  • ListView,RecyclerView适配器中绑定

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    ListItemBinding binding = ListItemBinding.inflate(layoutInflater, viewGroup, false);
    //or
    ListItemBinding binding = DataBindingUtil.inflate(layoutInflater, R.layout.list_item, viewGroup, false);

  • 如果通过其他方式填充的布局，需要调用bind方法

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    MyLayoutBinding binding =MyLayoutBinding.bind(viewRoot);

  • 另外的方式

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    ViewDataBinding binding = DataBindingUtil.inflate(LayoutInflater, layoutId,
        parent, attachToParent);
    ViewDataBinding binding = DataBindingUtil.bindTo(viewRoot, layoutId);

  • 布局中的views将没有设置id的会生成private final ID，设置id的会生成public final ID ，比findViewById速度更快

  • 生成的方法

    • variable

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      <data>
          <import type="android.graphics.drawable.Drawable"/>
          <variable name="user"  type="com.example.User"/>
          <variable name="image" type="Drawable"/>
          <variable name="note"  type="String"/>
      </data>

      public abstract com.example.User getUser();
      public abstract void setUser(com.example.User user);
      public abstract Drawable getImage();
      public abstract void setImage(Drawable image);
      public abstract String getNote();
      public abstract void setNote(String note);

    • ViewStubs
      因为在显示后会从view层级中消失，所以view的binding对象也会被回收

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      @NonNull
      public final android.databinding.ViewStubProxy viewStub;

      binding.viewStub.setOnInflateListener(new ViewStub.OnInflateListener() {
              @Override
              public void onInflate(ViewStub stub, View inflated) {
                   Log.e(TAG, "inflated=" + inflated + "  stub=" + stub);
              }
      });

      if (!binding.viewStub.isInflated()) {
         binding.viewStub.getViewStub().inflate();
      }

  • 事件处理两种方式

    • 方法引用

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       public class MyHandlers {
          public void onClickFriend(View view) { ... }
      }

      <?xml version="1.0" encoding="utf-8"?>
      <layout xmlns:android="http://schemas.android.com/apk/res/android">
         <data>
             <variable name="handlers" type="com.example.MyHandlers"/>
             <variable name="user" type="com.example.User"/>
         </data>
         <LinearLayout
             android:orientation="vertical"
             android:layout_width="match_parent"
             android:layout_height="match_parent">
             <TextView android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:text="@{user.firstName}"
                 android:onClick="@{handlers::onClickFriend}"/>
         </LinearLayout>
      </layout>

    • 监听绑定

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       public class Presenter {
          public void onSaveClick(Task task){}
      }
      绑定点击事件到类
        <?xml version="1.0" encoding="utf-8"?>
        <layout xmlns:android="http://schemas.android.com/apk/res/android">
            <data>
                <variable name="task" type="com.android.example.Task" />
                <variable name="presenter" type="com.android.example.Presenter" />
            </data>
            <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent">
                <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
                android:onClick="@{() -> presenter.onSaveClick(task)}" />
            </LinearLayout>
        </layout>

    • “@{() -> presenter.onSaveClick(task)}”可以忽略所有参数，也可以写上参数

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      android:onClick="@{(view) -> presenter.onSaveClick(task)}"

    • 如果类中有参数View

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       public class Presenter {
          public void onSaveClick(View view, Task task){}
      }
      绑定点击事件
      android:onClick="@{(theView) -> presenter.onSaveClick(theView, task)}"

    • 可以使用lambda表达式添加更多参数

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       public class Presenter {
          public void onCompletedChanged(Task task, boolean completed){}
      }

       <CheckBox android:layout_width="wrap_content" android:layout_height="wrap_content"
              android:onCheckedChanged="@{(cb, isChecked) -> presenter.completeChanged(task, isChecked)}" />

    • 如果类中的方法返回值不是void，点击事件的绑定表达式返回值应该和方法一样,如果返回值因为空对象不能判断，会返回对象的默认值

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       public class Presenter {
          public boolean onLongClick(View view, Task task){}
      }
        android:onLongClick="@{(theView) -> presenter.onLongClick(theView, task)}"

    • 可以使用void作为三元运算符的标记

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      android:onClick="@{(v) -> v.isVisible() ? doSomething() : void}"

    • 避免复杂监听，有些默认的点击事件处理的实现

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      SearchView setOnSearchClickListener(View.OnClickListener) android:onSearchClick

      ZoomControls setOnZoomInClickListener(View.OnClickListener) android:onZoomOut 

      ZoomControls setOnZoomOutClickListener(View.OnClickListener) android:onZoomOut
Layout Details

  • data元素标签下，可以导入多个类

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    <data>
        <import type="android.view.View">
    </data>

  • binding表达式中可以使用View

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    <TextView
       android:text="@{user.lastName}"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:visibility="@{user.isAdult ? View.VISIBLE : View.GONE}"/>

  • 导入类名冲突可以使用别名

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    <import type="android.view.View"/>
    <import type="com.example.real.estate.View"
            alias="Vista"/>

  • 导入类可以设置变量

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    <data>
        <import type="com.example.User"/>
        <import type="java.util.List"/>
        <variable name="user" type="User"/>
        <variable name="userList" type="List&lt;User&gt;"/>
    </data>

  • 引用静态变量和方法

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    <data>
        <import type="com.example.MyStringUtils"/>
        <variable name="user" type="com.example.User"/>
    </data>
    …
    <TextView
       android:text="@{MyStringUtils.capitalize(user.lastName)}"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>

  • 如果variable实现了android.databinding.Observable或者observable collection，应该在反映在type中，当没有实现上述接口时，变量将不会被观察Observer

  • 当横竖屏不同布局时，变量会整合，不同布局不要有命名冲突
  • binding 类的主要方法,其中context是来自rootview的context
    binding.getRoot().getContext()

  • 重命名Binding对象

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    <data class="MainAty">
     MainAty binding = DataBindingUtil.setContentView(this, R.layout.activity_main);

  • 设置Binding包名

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    当前应用包名，这种方式会导致Binding对view id绑定失效
     <data class=".MainAty">
     重新设置完整的包名
     <data class="com.main.MainAty">

  • include 绑定变量

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    <include layout="@layout/contact"
          bind:user="@{user}"/>

  • include布局元素不能作为merge的子元素

  • 表达式语法

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    exapmples:
    android:text="@{String.valueOf(index + 1)}"
    android:visibility="@{age < 13 ? View.GONE : View.VISIBLE}"
    android:transitionName='@{"image_" + id}'

  • 非空判断??

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    android:text="@{user.displayName ?? user.lastName}"
    等价于
    android:text="@{user.displayName != null ? user.displayName : user.lastName}"

  • 规避空指针异常，当variable为空时，属性值会显示相应的默认值

  • 集合

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    \<import type="java.util.List" />
            <import type="android.util.SparseArray" />
            <import type="java.util.Map" />
            <variable
                name="list"
                type="List&lt;String&gt;" />
            <variable
                name="sparse"
                type="SparseArray&lt;String&gt;" />
            <variable
                name="map"
                type="Map&lt;String,String&gt;" />
            <variable
                name="index"
                type="int" />
            <variable
                name="key"
                type="String" />

    android:text="@{list[index]}"

    android:text="@{sparse[index]}"

    android:text="@{map[key]}"

  • 字符串引用

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    android:text='@{map["firstName"]}'
    android:text="@{map[`firstName`}"
    android:text="@{map['firstName']}"

  • 表达式中的资源引用

数据对象

  • 数据自动更新通知机制

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    Observable objects
    Observable fields
    Observable collections

  • Observable Objects 继承自BaseObservable

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     public class BaseObservable implements Observable {
        private transient PropertyChangeRegistry mCallbacks;

        public BaseObservable() {
        }

        @Override
        public void addOnPropertyChangedCallback(OnPropertyChangedCallback callback) {
            synchronized (this) {
                if (mCallbacks == null) {
                    mCallbacks = new PropertyChangeRegistry();
                }
            }
            mCallbacks.add(callback);
        }

        @Override
        public void removeOnPropertyChangedCallback(OnPropertyChangedCallback callback) {
            synchronized (this) {
                if (mCallbacks == null) {
                    return;
                }
            }
            mCallbacks.remove(callback);
        }

        /**
         * Notifies listeners that all properties of this instance have changed.
         */
        public void notifyChange() {
            synchronized (this) {
                if (mCallbacks == null) {
                    return;
                }
            }
            mCallbacks.notifyCallbacks(this, 0, null);
        }

        /**
         * Notifies listeners that a specific property has changed. The getter for the property
         * that changes should be marked with {@link Bindable} to generate a field in
         * <code>BR</code> to be used as <code>fieldId</code>.
         *
         * @param fieldId The generated BR id for the Bindable field.
         */
        public void notifyPropertyChanged(int fieldId) {
            synchronized (this) {
                if (mCallbacks == null) {
                    return;
                }
            }
            mCallbacks.notifyCallbacks(this, fieldId, null);
        }
    }

  • 在getter()添加@Bindable注解,在setter()中添加notifyPropertyChanged(BR.lastName);

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     private static class User extends BaseObservable {
       private String firstName;
       private String lastName;
       @Bindable
       public String getFirstName() {
           return this.firstName;
       }
       @Bindable
       public String getLastName() {
           return this.lastName;
       }
       public void setFirstName(String firstName) {
           this.firstName = firstName;
           notifyPropertyChanged(BR.firstName);
       }
       public void setLastName(String lastName) {
           this.lastName = lastName;
           notifyPropertyChanged(BR.lastName);
       }
    }

    上面user例子，实现自动刷新UI

    @Bindable
    public boolean isAdult() {
          return isAdult;
    }

    public void setAdult(boolean adult) {
          isAdult = adult;
          notifyPropertyChanged(BR.adult);
     }
    user.isAdult = !user.isAdult;
    binding.setUser(user);

  • Observable Fields 不需要写setter() getter(),需要初始化new Observable***()

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    public class ObservableParcelable<T extends Parcelable> 
        extends ObservableField<T> implements Parcelable, Serializable

  • 实例

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     private static class User {
       public final ObservableField<String> firstName =
           new ObservableField<>();
       public final ObservableField<String> lastName =
           new ObservableField<>();
       public final ObservableInt age = new ObservableInt();
    }

    user.firstName.set("Google");
    int age = user.age.get();

  • Observable Collections

    • ObservableArrayMap

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      ObservableArrayMap<String, Object> observableMap = new ObservableArrayMap<>();
      observableMap.put("firstName", "Google");
      observableMap.put("lastName", "Inc.");
      observableMap.put("age", 17);
      binding.setObservableMap(observableMap);

      android:text='@{String.valueOf(observableMap["age"])}'

    • ObservableArrayList

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      ObservableArrayList<Object> list = new ObservableArrayList<>();
      list.add("Google");
      list.add("Inc.");
      list.add(17);
      binding.setObservableList(list);
        
      android:text="@{String.valueOf(observableList[index])}"
Advanced Binding 高级绑定

  • 动态变量
    RecyclerView.Adapter中在onBindViewHolder(VH, int)设置值,其中BindingHolder有一个getBinding()方法

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    public void onBindViewHolder(BindingHolder holder, int position) {
       final T item = mItems.get(position);
       holder.getBinding().setVariable(BR.item, item);
       holder.getBinding().executePendingBindings();
    }

  • 立即绑定
    当变量或观察者发生变化时，绑定会在下一帧绘制时发生改变，然而有时候需要强制重新绑定

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    android.databinding.ViewDataBinding.executePendingBindings()

  • 后台线程 可以在后台线程改变数据model，只要不是集合，数据绑定本地化每个变量，规避线程并发问题

属性设置

  • 自动设置属性
    布局文件

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    <ImageView
      android:layout_width="200dp"
      android:layout_height="200dp"
      android:scaleType="centerCrop"
      app:imageUrl="@{user.imageUrl}"
      app:placeHolder="@{@drawable/place}" />

  • 可以在任意类中绑定属性值设置方法，通常以模块，view自定义命名的Bindings类

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    @BindingAdapter(value = {"imageUrl", "placeHolder"}, requireAll = false)
    public static void setImageUrl(ImageView imageView, String url, Drawable placeHolder) {
       if (!TextUtils.isEmpty(url)){
    Glide.with(imageView.getContext()).load(url).into(imageView).onLoadStarted(placeHolder);
       } else {
          imageView.setImageDrawable(placeHolder);
       }
    }

  • 重命名setters，Android 实现了很多BindingAdapters,查看TextViewBinding

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    @BindingMethods({
            @BindingMethod(type = TextView.class, attribute = "android:autoLink", method = "setAutoLinkMask"),
            @BindingMethod(type = TextView.class, attribute = "android:drawablePadding", method = "setCompoundDrawablePadding"),
            @BindingMethod(type = TextView.class, attribute = "android:editorExtras", method = "setInputExtras"),
            @BindingMethod(type = TextView.class, attribute = "android:inputType", method = "setRawInputType"),
            @BindingMethod(type = TextView.class, attribute = "android:scrollHorizontally", method = "setHorizontallyScrolling"),
            @BindingMethod(type = TextView.class, attribute = "android:textAllCaps", method = "setAllCaps"),
            @BindingMethod(type = TextView.class, attribute = "android:textColorHighlight", method = "setHighlightColor"),
            @BindingMethod(type = TextView.class, attribute = "android:textColorHint", method = "setHintTextColor"),
            @BindingMethod(type = TextView.class, attribute = "android:textColorLink", method = "setLinkTextColor"),
            @BindingMethod(type = TextView.class, attribute = "android:onEditorAction", method = "setOnEditorActionListener"),
    })

  • 自定义设置方法

    • 有下面的方法setPadding(int left, int top, int right, int bottom)
      没有setPaddingLeft()，但是有android:paddingLeft属性

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      @BindingAdapter("android:paddingLeft")
      public static void setPaddingLeft(View view, int oldPadding, int newPadding) {
         if (oldPadding != newPadding) {
             view.setPadding(newPadding,
                             view.getPaddingTop(),
                             view.getPaddingRight(),
                             view.getPaddingBottom());
         }
      }

    • 一个抽象方法的接口或抽象类的事件处理,注意，此方法必须在自定义View中编写，下面的是官方文档代码示例

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       @BindingAdapter("android:onLayoutChange")
      public static void setOnLayoutChangeListener(View view, View.OnLayoutChangeListener oldValue,
             View.OnLayoutChangeListener newValue) {
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
              if (oldValue != null) {
                  view.removeOnLayoutChangeListener(oldValue);
              }
              if (newValue != null) {
                  view.addOnLayoutChangeListener(newValue);
              }
          }
      }

    • 如果是多个抽象方法的事件处理

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       @TargetApi(VERSION_CODES.HONEYCOMB_MR1)
      public interface OnViewDetachedFromWindow {
          void onViewDetachedFromWindow(View v);
      }

      @TargetApi(VERSION_CODES.HONEYCOMB_MR1)
      public interface OnViewAttachedToWindow {
          void onViewAttachedToWindow(View v);
      }
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     @BindingAdapter("android:onViewAttachedToWindow")
    public static void setListener(View view, OnViewAttachedToWindow attached) {
        setListener(view, null, attached);
    }

    @BindingAdapter("android:onViewDetachedFromWindow")
    public static void setListener(View view, OnViewDetachedFromWindow detached) {
        setListener(view, detached, null);
    }

    @BindingAdapter({"android:onViewDetachedFromWindow", "android:onViewAttachedToWindow"})
    public static void setListener(View view, final OnViewDetachedFromWindow detach,
            final OnViewAttachedToWindow attach) {
        if (VERSION.SDK_INT >= VERSION_CODES.HONEYCOMB_MR1) {
            final OnAttachStateChangeListener newListener;
            if (detach == null && attach == null) {
                newListener = null;
            } else {
                newListener = new OnAttachStateChangeListener() {
                    @Override
                    public void onViewAttachedToWindow(View v) {
                        if (attach != null) {
                            attach.onViewAttachedToWindow(v);
                        }
                    }

                    @Override
                    public void onViewDetachedFromWindow(View v) {
                        if (detach != null) {
                            detach.onViewDetachedFromWindow(v);
                        }
                    }
                };
            }
            final OnAttachStateChangeListener oldListener = ListenerUtil.trackListener(view,
                    newListener, R.id.onAttachStateChangeListener);
            if (oldListener != null) {
                view.removeOnAttachStateChangeListener(oldListener);
            }
            if (newListener != null) {
                view.addOnAttachStateChangeListener(newListener);
            }
        }
    }
    • 自定义View实现自定义监听事件处理
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       public class ColorPicker extends View {
          private int color;

          public ColorPicker(Context context) {
              super(context);
          }

          public ColorPicker(Context context, @Nullable AttributeSet attrs) {
              super(context, attrs);
          }

          public ColorPicker(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
              super(context, attrs, defStyleAttr);
          }

          public int getColor() {
              return color;
          }

          public void setColor(int color) {
              this.color = color;
              invalidate();
          }

          @Override
          protected void onDraw(Canvas canvas) {
              super.onDraw(canvas);
              canvas.drawColor(getResources().getColor(color));
          }

          public void removeListener(OnColorChangeListener oldListener) {
              oldListener.onColorChange(this, color);
              Log.e("color", "remove");
          }

          public void addListener(OnColorChangeListener newListener) {
              newListener.onColorChange(this, color);
              Log.e("color", "add");
          }

          public interface OnColorChangeListener {
              void onColorChange(ColorPicker view, int newColor);
          }

          @BindingAdapter("onColorChange")
          public static void setColorChangeListener(ColorPicker view,
                                                    ColorPicker.OnColorChangeListener oldListener,
                                                    ColorPicker.OnColorChangeListener newListener) {
              Log.e("oldListener", "="+oldListener);
              Log.e("newListener", "="+newListener);
              if (oldListener != null) {
                  view.removeListener(oldListener);
              }
              if (newListener != null) {
                  view.addListener(newListener);
              }
          }
      }

       布局引用
       <com.willkernel.www.databindingdemo.ColorPicker
                      android:id="@+id/colorPicker"
                      android:layout_width="100dp"
                      android:layout_height="100dp"
                      app:color="@{color}"
                      app:onColorChange="@{(v,color)->main.colorChanged(v,color)}" />
                      
      MainActivity handler中
      public void colorChanged(int color) {
                  Log.e(TAG, "colorChanged=" + color);
              }
          
      binding.setColor(R.color.colorAccent);
    转换

  • 对象类型转换,需要使用public static修饰方法

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    @BindingConversion
    public static String convertDateToText(Date date){
         DateFormat dateFormat=DateFormat.getDateInstance();
         return dateFormat.format(date);
    }

  • 自定义转换 颜色值int color转换为ColorDrawable,转换发生在setter level,不允许两种类型混合使用，int和drawable在同一个三元运算符中

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    <View
       android:background="@{isError ? @color/red : @color/white}"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>

    @BindingConversion
    public static ColorDrawable convertColorToDrawable(int color) {
       return new ColorDrawable(color);
    }
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