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。

    buildFeatures{
        dataBinding true
        // for view binding :
        // viewBinding 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", 10);
        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 

常用的方法：

• DataBindingUtil.inflate(inflater, R.layout.daily_data, container, false) 
• DataBindingUtil.bind(root) ,返回可能为空的绑定对象。

    lateinit var binding : DailyDataBinding

    override fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?
        ): View? {
        binding = DataBindingUtil.inflate(inflater, R.layout.daily_data, container, false)

        binding.dailyShare.setOnClickListener(this::onShareClicked)
        //...   
        return binding.root
    }

　　或者

    var binding : DailyBinding? = null
    fun initBinding(root : View){
        binding = DataBindingUtil.bind(root)
        binding?.page = page
        binding?.start = startTime
        //...          
    }

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  < 0){
                    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();
                }
            }
        },1000 * 1,1000 * 1);
    }
    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", 10);
        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 = 10;
        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 = 0 ; i < 32; ++i){
            ItemData item = new ItemData();
            item.title = "item" + i;
            switch (i){
                case 11: case 21:    case 31:
                case 1 : item.icon = R.mipmap.icon1;    break;

                case 12: case 22:    case 32:
                case 2 : item.icon = R.mipmap.icon2;    break;

                case 13: case 23:    case 33:
                case 3 : item.icon = R.mipmap.icon3;    break;

                case 14: case 24:    case 34:
                case 4 : item.icon = R.mipmap.icon4;    break;

                case 15: case 25:    case 35:
                case 5 : item.icon = R.mipmap.icon5;    break;

                case 16: case 26:
                case 6 : item.icon = R.mipmap.icon6;    break;

                case 17: case 27:
                case 7 : item.icon = R.mipmap.icon7;    break;

                case 18: case 28:
                case 8 : item.icon = R.mipmap.icon8;    break;

                case 19: case 29:
                case 9 : 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 ： appuildgeneratedap_generated_sourcesdebugoutcomexampledatabinddatabinding 目录下，

　　comexampledatabind  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

5.4 修改生成的绑定类的名字

<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <data class="AAAAAAA">
        <import type="android.view.View" />
        <import type="com.example.databind.Exts" />
    </data>
    <androidx.constraintlayout.widget.ConstraintLayout
        android:clickable="true"
        android:background="#ffffff"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
...

　　这个示例 在当前模块的 databinding 包中生成绑定类  AAAAAAA 

    <data class=".BBBBBB">
        …
    </data>

　　这个示例 在模块包中生成绑定类  BBBBBB

    <data class="com.example.CCC">
        …
    </data>

　　这个 示例在 com.example 包中创建绑定类 CCC

5.3 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, 3);
        sViewsWithIds.put(R.id.textView, 4);
    }
    // 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, 5, sIncludes, sViewsWithIds));
    }
    private Frgmt1BindingImpl(androidx.databinding.DataBindingComponent bindingComponent, View root, Object[] bindings) {
        super(bindingComponent, root, 0
            , (android.widget.ImageView) bindings[3]
            , (android.widget.TextView) bindings[1]
            , (android.widget.TextView) bindings[4]
            , (android.widget.TextView) bindings[2]
            );
        this.key.setTag(null);
        this.mboundView0 = (androidx.constraintlayout.widget.ConstraintLayout) bindings[0];
        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 != 0) {
                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 = 0;
        synchronized(this) {
            dirtyFlags = mDirtyFlags;
            mDirtyFlags = 0;
        }
        java.lang.String stringValueOfDataValue = null;
        java.lang.String dataKey = null;
        com.example.databind.Data data = mData;
        int dataValue = 0;

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



                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) != 0) {
            // 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
}

5.4 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);
    }