DataBinding使用篇

﹏ヽ暗。殇╰゛Y 2022-09-12 09:48 219阅读 0赞

> DataBinding 是谷歌官方发布的一个框架,DataBinding 能够省去我们一直以来的 findViewById() 步骤，大量减少 Activity 内的代码，数据能够单向或双向绑定到 layout 文件中，有助于防止内存泄漏，而且能自动进行空检测以避免空指针异常。

**要将应用配置为使用数据绑定，请在应用模块的 build.gradle 文件中添加 dataBinding 元素，如以下示例所示：**

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

## 1、基本使用 ##

### 1.1 布局中的用法 ###

**选中根布局option+回车，点击 “Convert to data binding layout”自动生成如下格式，或者手动写成下面的格式：layout包裹 data 和实际的布局，data 标签的作用就像一个桥梁搭建了 View 和 Model 之间的通道**

<?xml version="1.0" encoding="utf-8"?>
    <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>
    
        </data>
    
        <androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent">
    
    
        </androidx.constraintlayout.widget.ConstraintLayout>
    </layout>

**在 variable 标签里声明要使用到的变量名、类的全路径**

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

**也可以通过import来引入包名**

<data>
            <import type="com.example.myapplication.model.User"/>
    
            <variable name="user" type="User" />
        </data>

**还可以通过alias给类设置别名**

<data>
            <import alias="LoginBean" type="com.example.myapplication.model.User"/>
    
            <variable name="user" type="LoginBean" />
        </data>

**其他类型的数据**

**通过@\{\}的方式来给控件赋值**

**@\{\}中使用表达式**

android:text="@{String.valueOf(age)}"
    android:visibility="@{age < 13 ? View.GONE : View.VISIBLE}"
    android:text='@{"iname:" +user.name}'

### 1.2 代码中的用法 ###

**通过DataBindingUtil获取到Binding对象，创建数据并设置给Binding对象**

public class TestDataBinding extends Activity  { 
        private User user;
        private ActivityDatabindingBinding activityDatabindingBinding;
        
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            activityDatabindingBinding = DataBindingUtil.setContentView(
            this,R.layout.activity_databinding);
            user = new User();
            user.setName("databing");
            user.setPassword("test123456");
            activityDatabindingBinding.setUserBean(user);
        }
    }

**Binding对象的名字是根据布局文件名字+Binding生成的，你还可以在xml中自定义Binding对象的名字**  
**1、设置自定义的名称**

**2、得到Binddings对象**

public class TestDataBinding extends Activity  { 
        private User user;
        private CustomBinding customBinding;
        
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            customBinding = DataBindingUtil.setContentView(this,R.layout.activity_databinding);
        }
    
    }

## 2 单向数据绑定 ##

**单向数据绑定的方式有三种：BaseObservable、ObservableField、ObservableCollection，都能实现数据变化自动驱动 UI 刷新。**

### 2.1 BaseObservable ###

**继承BaseObservable类，通过notifyPropertyChanged和notifyChange()来实现刷新**  
**notifyPropertyChanged:只刷新属于自己的UI**  
**notifyChange:刷新所有UI**

public class User extends BaseObservable { 
        private String name;
        private String password;
        public String anything;
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
            notifyPropertyChanged(BR.userBean);		//只刷新属于自己的UI
        }
    
        public String getPassword() { 
            return password;
        }
    
        public void setPassword(String password) { 
            this.password = password;
            notifyChange();							//刷新所有UI
        }
    }

### 2.2 ObservableField ###

**ObservableField 可以理解为是对 BaseObservable 进行了封装，ObservableField提供了get、set方法，可以拿到值和更新值来达到更新UI效果**

**数据类**

public class User{ 
        private ObservableField<String> name;
        private ObservableField<String> password;
        private ObservableField<Integer> intData;
        private ObservableField<Short> shortData;
        private ObservableField<Boolean> booleanData;
        private ObservableField<Byte> byteData;
    
        public ObservableField<String> getName() { 
            return name;
        }
    
        public ObservableField<String> getPassword() { 
            return password;
        }
    
        public void setName(ObservableField<String> name) { 
            this.name = name;
        }
    
        public void setPassword(ObservableField<String> password) { 
            this.password = password;
        }
    }

**操作**

protected void onCreate(@Nullable Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            customBinding = DataBindingUtil.setContentView(this,R.layout.activity_databinding);
            user = new User();
            user.setName(new ObservableField<String>("databing"));
            user.setPassword(new ObservableField<String>("test123456"));
            customBinding.setUserBean(user);
            customBinding.setListener(new Listenter());
            customBinding.setClickListener(this);
        }
    
        public class Listenter{ 
    
            public void clickListner(){ 
                Toast.makeText(TestDataBinding.this,"点击",Toast.LENGTH_SHORT).show();
                user.getName().set("123456");
                user.getPassword().set("12");
            }
    
            public String getPsw(){ 
                return user.getPassword().get();
            }
        }

### 2.3 ObservableCollection ###

**如果用到 Map 或者是 List，同样 DataBinding 还提供了 ObservableMap 和 ObservableList**

**ObservableMap 的使用  
1、声明mapkey和value类型的时候不支持尖括号<>,用符号代替  
2、使用变量的时候单引号包裹 android:text=’@\{map\[“name”\]\}'**

**初始化map**

private ObservableMap<String,String> observableMap;
     observableMap = new ObservableArrayMap<>();
            observableMap.put("name","databing");
            observableMap.put("psw","test123456");
            customBinding.setMap(observableMap);
    
     public class Listenter{ 
    
            public void clickListner(){ 
                Toast.makeText(TestDataBinding.this,"点击",Toast.LENGTH_SHORT).show();
                user.getName().set("123456");
                user.getPassword().set("12");
                observableMap.put("name","chage");
                observableMap.put("psw","chage123");
            }
    
            public String getPsw(){ 
                return user.getPassword().get();
            }
        }

**ObservableList 的使用  
1、声明List类型的时候不支持尖括号<>,用符号代替**

**初始化list**

private ObservableList<String> observableList;
     observableList = new ObservableArrayList<>();
            observableList.add("databing");
            observableList.add("test123456");
            customBinding.setList(observableList);
    
     public class Listenter{ 
    
            public void clickListner(){ 
                Toast.makeText(TestDataBinding.this,"点击",Toast.LENGTH_SHORT).show();
                
                observableList.clear();
                observableList.put("name","chage");
                observableList.put("psw","chage123");
            }
        }

## 3 双向数据绑定 ##

**双向绑定：数据改变UI跟新，UI更新同时数据也要更新**  
**使用方式@\{\}“改成了”@=\{\}"，**

public class User extends BaseObservable{ 
        private ObservableField<String> name;
        private ObservableField<String> password;
        
        public ObservableField<String> getName() { 
            return name;
        }
    
        public ObservableField<String> getPassword() { 
            return password;
        }
    
        public void setName(ObservableField<String> name) { 
            this.name = name;
        }
    
        public void setPassword(ObservableField<String> password) { 
            this.password = password;
        }
    }

## 4 事件使用 ##

**声明事件**

public  class Listenter{ 
    
            public void customClickListener(User user){ 
                Toast.makeText(TestDataBinding.this,"点击",Toast.LENGTH_SHORT).show();
                user.getName().set("change");
                user.getPassword().set("change123456");
    
            }
    
            public void customAfterTextChanged() { 
                customBinding.tvChangePsw.setText(user.getPassword().get());
            }
    
    
            public void onClick(View v) { 
                Toast.makeText(TestDataBinding.this,"点击",Toast.LENGTH_SHORT).show();
                user.getName().set("change");
                user.getPassword().set("change123456");
    
            }
    
            public void afterTextChanged(Editable s) { 
                customBinding.tvChangePsw.setText(user.getPassword().get());
            }
    
    
            public String getPsw(){ 
                return user.getPassword().get();
            }
        }

**在xml中使用**

<EditText ... android:afterTextChanged="@{()->listener.customAfterTextChanged()}" android:text="@={userBean.password}" />
    
    <Button ... android:text="@{listener.psw}" android:textSize="18dp" android:onClick="@{()->listener.customClickListener(user)}" />
    
    
    <EditText ... android:afterTextChanged="@{listener.afterTextChanged}" android:text="@={userBean.password}" />
    
    <Button ... android:text="@{listener.psw}" android:textSize="18dp" android:onClick="@{listener.onClick}" />

## 5 include布局 ##

**要被include的布局**

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
        
        <data>
            <import type="com.example.myapplication.model.User"/>
            <variable name="xxxxx" type="User" />
        </data>
        
        <RelativeLayout android:id="@+id/rl_title_bar" android:layout_width="match_parent" android:layout_height="50dp" >
        <TextView android:id="@+id/tv_title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@{userBean.name}" android:textColor="#333333" android:textSize="20dp" android:gravity="center" android:layout_centerInParent="true" />
        </RelativeLayout>
    </layout>

**父布局**

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
        
        <data class="CustomBinding">
            <import type="com.example.myapplication.model.User"/>
            <variable name="userBean" type="User" />
        </data>
        
        <androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent">
            
            <include app:xxxxx="@{userBean}" layout="@layout/activity_databinding_include" />
            
        </androidx.constraintlayout.widget.ConstraintLayout>
    </layout>

## 6 在列表中使用 ##

**Activity**

public class TestRecyclerViewBinding extends Activity { 
        private RvBinding rvBinding;
        private RvAdapter mAdapter;
        private List<NewsBean> data = new ArrayList<>();
    
        public static void intentTo(Context context) { 
            Intent intent = new Intent(context, TestRecyclerViewBinding.class);
            context.startActivity(intent);
        }
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            rvBinding = DataBindingUtil.setContentView(this,R.layout.activity_databinding_rv);
            initRv();
        }
    
        private void initRv(){ 
            rvBinding.rv.setLayoutManager(new LinearLayoutManager(this));
            data.add(new NewsBean("中方回应阿富汗塔利班成立新政府","9月7日，阿富汗塔利班宣布成立新政府。8日，外交部发言人汪文斌回应：阿塔成立新政府，是恢复国内秩序和战后重建必要一..."));
            data.add(new NewsBean("江西“皮箱藏尸案”嫌疑人被抓获","9月7日，江西吉安泰和县发生一起重大刑事案件，陕西宁强县男子谢磊有重大作案嫌疑。目前，犯罪嫌疑人已抓获."));
            data.add(new NewsBean("人民日报评论明确三个“没有变”","9月8日，《人民日报》头版推出评论员文章《坚持监管规范和促进发展两手并重、两手都要硬》，明确指出非公有制经济三个“没有变”。 "));
            data.add(new NewsBean("国庆节放假调休安排来了","2021年国庆节放假安排：10月1日（星期五）至7日（星期四）放假调休，共7天。9月26日（星期日）、10月9日（星期六）上班。"));
            mAdapter = new RvAdapter(this,data);
            rvBinding.rv.setAdapter(mAdapter);
        }
    }

**Adapter**

public class RvAdapter extends RecyclerView.Adapter<RvAdapter.ItemViewHolder> { 
        private Context mContext;
        private List<NewsBean> mData;
    
        public RvAdapter(Context context, List<NewsBean> data){ 
            mContext = context;
            mData = data;
        }
    
        @NonNull
        @Override
        public ItemViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) { 
            ViewDataBinding binding = DataBindingUtil.inflate(LayoutInflater.from(mContext), R.layout.layout_rv_item,parent,false);
            return new ItemViewHolder(binding);
        }
    
        @Override
        public void onBindViewHolder(@NonNull ItemViewHolder holder, int position) { 
            ViewDataBinding binding = holder.getBinding();
            binding.setVariable(BR.news,mData.get(position));
    // binding.executePendingBindings();//强制绑定同步更新数据
        }
    
    
    
        @Override
        public int getItemCount() { 
            int size = 0;
            if(mData!=null){ 
                size=mData.size();
            }
            return size;
        }
    
        public static class ItemViewHolder extends RecyclerView.ViewHolder{ 
            private ViewDataBinding mBinding;
    
            public ItemViewHolder(ViewDataBinding binding) { 
                super(binding.getRoot());
                mBinding = binding;
            }
    
            public ViewDataBinding getBinding(){ 
                return mBinding;
            }
    
        }
    
    }

**Item布局**

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
        <data>
            <variable name="news" type="com.example.myapplication.model.NewsBean" />
        </data>
    
        <androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="100dp">
    
            <ImageView android:id="@+id/iv_news" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="15dp" android:background="@mipmap/ic_launcher_round" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintLeft_toLeftOf="parent" app:layout_constraintTop_toTopOf="parent" />
    
            <TextView android:id="@+id/tv_title" android:text="@{news.title}" android:layout_width="0dp" android:layout_marginLeft="15dp" android:layout_marginRight="15dp" android:layout_height="wrap_content" app:layout_constraintLeft_toRightOf="@+id/iv_news" app:layout_constraintTop_toTopOf="@+id/iv_news" />
    
            <TextView android:id="@+id/tv_sub_title" android:layout_width="0dp" android:text="@{news.subTitle}" android:lines="2" android:maxLines="2" android:layout_marginLeft="15dp" android:layout_marginRight="15dp" android:layout_height="wrap_content" app:layout_constraintTop_toBottomOf="@+id/tv_title" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintRight_toRightOf="parent" app:layout_constraintLeft_toRightOf="@+id/iv_news" />
    
    
        </androidx.constraintlayout.widget.ConstraintLayout>
    
    </layout>

## 7 @BindingAdapter自定义属性注解 ##

dataBinding中自定义属性依赖于注解@BindingAdapter

1.  作用于方法，这个方法可以写在任何地方
2.  这个注解面向一个public static方法
3.  \{\}内部表示使用时这个属性的名字。例如：@BindingAdapter(\{“imageUrl”\})，imageUrl为属性的名称

用加载图片做例子

**java代码**

public class ImageHelper { 
        @BindingAdapter({ "imageUrl"})
        public static void loadImage(ImageView imageView,String url){ 
            Glide.with(imageView.getContext())
                    .load(url)
                    .error(R.mipmap.ff)
                    .placeholder(R.mipmap.ff)
                    .into(imageView);
        }

public class MainActivity extends AppCompatActivity { 
    
        private String Url = "https://c-ssl.duitang.com/uploads/item/201908/27/20190827152805_sfsxr.thumb.700_0.jpg"；
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            ActivityMainBinding binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
    
            binding.setUrl(Url);
          
        }
    }

**布局**

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">
    
        <data>
    
            <variable
                name="url"
                type="String" />
    
        </data>
        <LinearLayout
            xmlns:tools="http://schemas.android.com/tools"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            >
    
            <ImageView
                android:layout_width="90dp"
                android:layout_height="90dp"
                android:scaleType="centerCrop"
                app:imageUrl="@{url}"/>
    
        </LinearLayout>
    </layout>

@BindingAdapter自定义属性注解还可设置多个参数，很多场景都能使用，具体用法结合自己自己的应用场景来定义吧。