android 数据绑定(1)Ativity、Fragment、Item绑定数据源

1.简介

官方文档：

　　 https://developer.android.com/topic/libraries/data-binding

官方示例：

　　https://github.com/android/databinding-samples

作用：

　　把layout 与 数据对象关联，将layout上的组件与对象的成员绑定.让layout上的组件的值来自数据对象。如：

    <TextView android:text="@{data.value}" />

2.简单用法:绑定Activity与数据源

2.1 打开绑定选项

　　只能在主module的 build.gradle 中打开，即使主module代码没有使用数据绑定，而他依赖的module使用了数据绑定，也要在主module中打开。

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

2.2 布局 activity_main.xml

 <?xml version="1.0" encoding="utf-8"?>
 <layout xmlns:android="http://schemas.android.com/apk/res/android">
     <data>
         <variable name="data" type="com.example.databind.Data" />      <!--声明的对象data-->
         <variable name="click" type="com.example.databind.Click" />
     </data>
     <androidx.constraintlayout.widget.ConstraintLayout >

         <TextView android:text="@{data.value, default = value}" />      <!--值来自数据对象data-->
         <Button android:onClick="@{() -> click.onStartClick(data)}" />

     </androidx.constraintlayout.widget.ConstraintLayout>
 </layout>

其中

• 跟元素<layout> 包含 元素 <data>和 跟布局<ConstraintLayout >
• <data>元素用来定义layout使用的数据源,可以使用稍微复杂语法，如<import ...>，见第4、5行。
• layout上的组件使用@{数据源名.成员}指定值,@{}内可以使用简单的的绑定表达式,如第10行。

2.3 数据对象 Data.java

 package com.example.databind;

 public class Data {
     public String   key;
     public int      value;

     public Data(String key, int value){
         this.key = key;
         this.value = value;
     }

     @Override
     public String toString() {
         return "key = " + key + " value = " + value;
     }
 }

2.4 建立绑定关系

 package com.example.databind;
 import android.os.Bundle;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.databinding.DataBindingUtil;

 import com.example.databind.databinding.ActivityMainBinding;

 public class MainActivity extends AppCompatActivity {

     private ActivityMainBinding binding;
     private Data                data;

     private void init(){
         data = new Data("time", );
         binding = DataBindingUtil.setContentView(MainActivity.this, R.layout.activity_main);
         binding.setData(data);
         binding.setClick(new Click(binding));
     }

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         init();
     }
 }

关于其中的 ActivityMainBinding ：

• 第15行得到了把一个activity和一个布局关联，得到一个绑定对象 ActivityMainBinding,它是绑定框架生成的，见5。
• 写完layout后 Rebuild Project 一下 就可以生成它。

3. 绑定Fragment与数据源

3.1 布局文件

 <?xml version="1.0" encoding="utf-8"?>
 <layout xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:android="http://schemas.android.com/apk/res/android">
     <data >
         <variable name="data" type="com.example.databind.Data" />
         <variable name="click" type="com.example.databind.Click" />
     </data>

     <androidx.constraintlayout.widget.ConstraintLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:clickable="true"
         >
         <TextView
             android:id="@+id/title"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginTop="16dp"
             android:text="Hello Data Binding !"
             app:layout_constraintLeft_toLeftOf="parent"
             app:layout_constraintRight_toRightOf="parent"
             app:layout_constraintTop_toTopOf="parent" />

         <TextView
             android:id="@+id/key"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginTop="16dp"
             android:text="@{data.key, default = key}"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintEnd_toStartOf="@+id/value"
             app:layout_constraintTop_toBottomOf="@+id/title"
             app:layout_constraintHorizontal_chainStyle="packed"
             />

         <TextView
             android:id="@+id/value"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginStart="16dp"
             android:layout_marginLeft="16dp"
             android:text="@{String.valueOf(data.value),default = value}"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toEndOf="@+id/key"
             app:layout_constraintTop_toTopOf="@+id/key" />

         <Button
             android:id="@+id/start"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginTop="16dp"
             android:onClick="@{() -> click.onStartClick(data)}"
             android:text="start"
             android:textAllCaps="false"
             app:layout_constraintEnd_toStartOf="@+id/stop"
             app:layout_constraintHorizontal_chainStyle="packed"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@+id/key" />

         <Button
             android:id="@+id/stop"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginStart="16dp"
             android:layout_marginLeft="16dp"
             android:onClick="@{() -> click.onStopClicked(data)}"
             android:text="stop"
             android:textAllCaps="false"
             app:layout_constraintBottom_toBottomOf="@+id/start"
             app:layout_constraintEnd_toStartOf="@+id/reset"
             app:layout_constraintStart_toEndOf="@+id/start"
             app:layout_constraintTop_toTopOf="@+id/start" />

         <Button
             android:id="@+id/reset"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginStart="16dp"
             android:layout_marginLeft="16dp"
             android:text="reset"
             android:textAllCaps="false"
             app:layout_constraintBottom_toBottomOf="@+id/start"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toEndOf="@+id/stop"
             app:layout_constraintTop_toTopOf="@+id/start"
             app:layout_constraintVertical_bias="1.0" />

         <Button
             android:id="@+id/list_fragment"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginTop="32dp"
             android:text="list fragment"
             android:textAllCaps="false"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@+id/stop" />

         <EditText
             android:id="@+id/editText"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginTop="32dp"
             android:ems="10"
             android:inputType="textPersonName"
             android:text="Name"
             app:layout_constraintEnd_toEndOf="@+id/list_fragment"
             app:layout_constraintStart_toStartOf="@+id/list_fragment"
             app:layout_constraintTop_toBottomOf="@+id/list_fragment" />

     </androidx.constraintlayout.widget.ConstraintLayout>

 </layout>

3.2 数据类

Data.java

 package com.example.databind;

 public class Data {
     public String   key;
     public int      value;

     public Data(String key, int value){
         this.key = key;
         this.value = value;
     }

     @Override
     public String toString() {
         return "key = " + key + " value = " + value;
     }
 }

click.java

 package com.example.databind;
 import android.util.Log;
 import androidx.databinding.ViewDataBinding;
 import java.util.Timer;
 import java.util.TimerTask;

 public class Click {
     ViewDataBinding     binding;
     private Timer       timer;

     public void onStartClick(final Data data){
         timer = new Timer();
         timer.schedule(new TimerTask() {
             @Override
             public void run() {
                 if (--data.value  < ){
                     cancel();
                     return;
                 }
                 Log.e("ActivityMainBinding","data : " + data);
                 data.key = "left";
 //                binding.setData(data);
 //                binding.notifyChange();
 //                binding.notifyPropertyChanged(R.id.value);
 //                binding.value.invalidate();
                 if (!binding.hasPendingBindings()){
                     binding.invalidateAll();
                 }
             }
         }, * , * );
     }
     public void onStopClicked(Data data){
         cancel();
     }
     private void cancel(){
         if (timer != null){
             timer.cancel();
             timer = null;
         }
     }
     public Click(ViewDataBinding binding){
         this.binding = binding;
     }
 }

3.3 绑定

 package com.example.databind;

 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;

 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.databinding.DataBindingUtil;
 import androidx.databinding.ViewDataBinding;
 import androidx.fragment.app.Fragment;

 import butterknife.ButterKnife;
 import butterknife.OnClick;

 public class MainFrgmt extends Fragment {

     ViewDataBinding             binding;
     private Data                data;

     private void init(){
         data = new Data("time", );
         binding.setVariable(BR.data,data);
         binding.setVariable(BR.click,new Click(binding));
     }
     @Nullable
     @Override
     public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
         binding = DataBindingUtil.inflate(inflater,R.layout.frgmt_main,container,false);
         View view = binding.getRoot();
         ButterKnife.bind(this,view);
         init();
         return view;
     }

     @OnClick(R.id.reset)
     public void onResetClicked(View view){
         data.key = "time";
         data.value = ;
         binding.invalidateAll();
     }
 }

其中：

• 第31行创建绑定对象 binding
• 第24、25行设置绑定的数据对象，其中的BR是绑定库生成的一个类，其中包含<data>中声明的变量的id。如data的id就是BR.data
• 第41行更新数据对象

4.Item绑定数据源

4.1 item布局

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

     <data>
         <variable name="item" type="com.example.databind.list.ItemData" />
     </data>

     <LinearLayout
         android:orientation="horizontal"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         >
         <ImageView
             android:id="@+id/item_icon"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginLeft="16dp"
             android:layout_marginStart="16dp"
             android:layout_marginTop="8dp"
             android:layout_marginBottom="8dp"
             android:layout_gravity="center_vertical"
             android:layout_weight="1"
             app:imageSrc="@{item.icon}" />
         <TextView
             android:id="@+id/item_title"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_weight="5"
             android:layout_marginLeft="32dp"
             android:layout_marginStart="32dp"
             android:layout_marginRight="8dp"
             android:layout_marginEnd="8dp"
             android:layout_gravity="center_vertical"
             android:gravity="left|center_vertical"
             android:textAllCaps="false"
             android:textSize="16sp"
             android:layout_marginTop="8dp"
             android:layout_marginBottom="8dp"
             android:text="@{item.title,default = item}" />
     </LinearLayout>

 </layout>

4.2 数据类

 package com.example.databind.list;

 public class ItemData {
     public String   title;
     public int      icon;
 }

4.3 adapter

 package com.example.databind.list;

 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.ImageView;

 import androidx.annotation.NonNull;
 import androidx.databinding.BindingAdapter;
 import androidx.databinding.DataBindingUtil;
 import androidx.recyclerview.widget.RecyclerView;

 import com.example.databind.R;
 import com.example.databind.databinding.ListItemBinding;

 import java.util.ArrayList;
 import java.util.List;

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

     private List<ItemData>  datas = new ArrayList<>();

     public void initData(){
         for (int i =  ; i < ; ++i){
             ItemData item = new ItemData();
             item.title = "item" + i;
             switch (i){
                 case : case :    case :
                 case  : item.icon = R.mipmap.icon1;    break;

                 case : case :    case :
                 case  : item.icon = R.mipmap.icon2;    break;

                 case : case :    case :
                 case  : item.icon = R.mipmap.icon3;    break;

                 case : case :    case :
                 case  : item.icon = R.mipmap.icon4;    break;

                 case : case :    case :
                 case  : item.icon = R.mipmap.icon5;    break;

                 case : case :
                 case  : item.icon = R.mipmap.icon6;    break;

                 case : case :
                 case  : item.icon = R.mipmap.icon7;    break;

                 case : case :
                 case  : item.icon = R.mipmap.icon8;    break;

                 case : case :
                 case  : item.icon = R.mipmap.icon9;    break;
                 default: item.icon = R.mipmap.icon0;    break;
             }
             datas.add(item);
         }
     }

     @BindingAdapter({"imageSrc"})
     public static void setImage(ImageView view, int icon){
         view.setImageResource(icon);
     }

     @NonNull
     @Override
     public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
         LayoutInflater inflater = LayoutInflater.from(parent.getContext());
         View view = inflater.inflate(R.layout.list_item,parent,false);
         BindHolder holder = new BindHolder(view);

         return holder;
     }

     @Override
     public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
         BindHolder bh = (BindHolder) holder;
         ItemData item = datas.get(position);
         ListItemBinding binding = DataBindingUtil.bind(bh.itemView);
         binding.setItem(item);
     }

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

     public static class BindHolder extends RecyclerView.ViewHolder{

         public BindHolder(@NonNull View itemView) {
             super(itemView);
         }
     }
 }

5.ActivityMainBinding 等绑定类哪来的？

5.1 他们是绑定框架生成的接口

位置：

以 Frgmt1Binding 为例，它的实现在 ： app\build\generated\ap_generated_sources\debug\out\com\example\databind\databinding 目录下，

　　com\example\databind  是包名，如下：

默认的命名规则：

　　布局文件名按Pascal命名方法(忽略下划线_) + Binding , 如布局文件是 Frgmt1.xml 那么生成的类就是 Frgmt1Binding

5.2 代码

 package com.example.databind.databinding;
 import com.example.databind.R;
 import com.example.databind.BR;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import android.view.View;
 @SuppressWarnings("unchecked")
 public class Frgmt1BindingImpl extends Frgmt1Binding  {

     @Nullable
     private static final androidx.databinding.ViewDataBinding.IncludedLayouts sIncludes;
     @Nullable
     private static final android.util.SparseIntArray sViewsWithIds;
     static {
         sIncludes = null;
         sViewsWithIds = new android.util.SparseIntArray();
         sViewsWithIds.put(R.id.imageView, );
         sViewsWithIds.put(R.id.textView, );
     }
     // views
     @NonNull
     private final androidx.constraintlayout.widget.ConstraintLayout mboundView0;
     // variables
     // values
     // listeners
     // Inverse Binding Event Handlers

     public Frgmt1BindingImpl(@Nullable androidx.databinding.DataBindingComponent bindingComponent, @NonNull View root) {
         this(bindingComponent, root, mapBindings(bindingComponent, root, , sIncludes, sViewsWithIds));
     }
     private Frgmt1BindingImpl(androidx.databinding.DataBindingComponent bindingComponent, View root, Object[] bindings) {
         super(bindingComponent, root,
             , (android.widget.ImageView) bindings[]
             , (android.widget.TextView) bindings[]
             , (android.widget.TextView) bindings[]
             , (android.widget.TextView) bindings[]
             );
         this.key.setTag(null);
         this.mboundView0 = (androidx.constraintlayout.widget.ConstraintLayout) bindings[];
         this.mboundView0.setTag(null);
         this.value.setTag(null);
         setRootTag(root);
         // listeners
         invalidateAll();
     }

     @Override
     public void invalidateAll() {
         synchronized(this) {
                 mDirtyFlags = 0x4L;
         }
         requestRebind();
     }

     @Override
     public boolean hasPendingBindings() {
         synchronized(this) {
             if (mDirtyFlags != ) {
                 return true;
             }
         }
         return false;
     }

     @Override
     public boolean setVariable(int variableId, @Nullable Object variable)  {
         boolean variableSet = true;
         if (BR.click == variableId) {
             setClick((com.example.databind.Click) variable);
         }
         else if (BR.data == variableId) {
             setData((com.example.databind.Data) variable);
         }
         else {
             variableSet = false;
         }
             return variableSet;
     }

     public void setClick(@Nullable com.example.databind.Click Click) {
         this.mClick = Click;
     }
     public void setData(@Nullable com.example.databind.Data Data) {
         this.mData = Data;
         synchronized(this) {
             mDirtyFlags |= 0x2L;
         }
         notifyPropertyChanged(BR.data);
         super.requestRebind();
     }

     @Override
     protected boolean onFieldChange(int localFieldId, Object object, int fieldId) {
         switch (localFieldId) {
         }
         return false;
     }

     @Override
     protected void executeBindings() {
         long dirtyFlags = ;
         synchronized(this) {
             dirtyFlags = mDirtyFlags;
             mDirtyFlags = ;
         }
         java.lang.String stringValueOfDataValue = null;
         java.lang.String dataKey = null;
         com.example.databind.Data data = mData;
         int dataValue = ;

         if ((dirtyFlags & 0x6L) != ) {

                 if (data != null) {
                     // read data.key
                     dataKey = data.key;
                     // read data.value
                     dataValue = data.value;
                 }

                 // read String.valueOf(data.value)
                 stringValueOfDataValue = java.lang.String.valueOf(dataValue);
         }
         // batch finished
         if ((dirtyFlags & 0x6L) != ) {
             // api target 1

             androidx.databinding.adapters.TextViewBindingAdapter.setText(this.key, dataKey);
             androidx.databinding.adapters.TextViewBindingAdapter.setText(this.value, stringValueOfDataValue);
         }
     }
     // Listener Stub Implementations
     // callback impls
     // dirty flag
     private  long mDirtyFlags = 0xffffffffffffffffL;
     /* flag mapping
         flag 0 (0x1L): click
         flag 1 (0x2L): data
         flag 2 (0x3L): null
     flag mapping end*/
     //end
 }

5.3 可以直接使用 ViewDataBinding

     private ViewDataBinding binding;

     private void init(View view){
         binding = DataBindingUtil.bind(view);
         MainActivity main = (MainActivity) getActivity();
         binding.setVariable(BR.data,main.data);
     }