Android_Data_Binding—————–(1)

主要优势

  1.去除Activity/Fragment中的UI代码  2.性能超过手写,安全  3.执行在主线程中

类似方案

  ButterKnife  Android Annotations  RoboBinding

使用- Gradle

  App module - build.gradle  android{    ...    dataBinding{       enabled = true    }  }

消除View的查找

我们需要通过<layout>标签包裹原有的布局<layout xmlns:android="http://schemas.android.com/apk/res/android"        xmlns:tools="http://schemas.android.com/tools">    <RelativeLayout            android:layout_width="match_parent"            android:layout_height="match_parent"            android:paddingLeft="@dimen/activity_horizontal_margin"            android:paddingRight="@dimen/activity_horizontal_margin"            android:paddingTop="@dimen/activity_vertical_margin"            android:paddingBottom="@dimen/activity_vertical_margin"            tools:context=".MainActivity">        <TextView                android:id="@+id/tvLabel"                android:layout_width="wrap_content"                android:layout_height="wrap_content"/>    </RelativeLayout></layout>

使用binding来填充布局

public class MainActivity extends AppCompatActivity {    // Store the binding    private ActivityMainBinding binding;//  ActivityMainBinding类 会根据activity_main.xml自动生成    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        // Inflate the content view (replacing `setContentView`)        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);        // Store the field now if you'd like without any need for casting        TextView tvLabel = binding.tvLabel;        tvLabel.setAllCaps(true);        // Or use the binding to update views directly on the binding        binding.tvLabel.setText("Foo");    }}

一种绑定数据的方法

public class User {   public String firstName;   public String lastName;//   public User(String firstName, String lastName){           this.firstName = firstName;           this.lastName = lastName;       }//       public String getFirstName() {           return firstName;       }//       public String getLastName() {           return lastName;       }}

从对象中加载数据

需要在data下声明 variable节点

<layout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools">    <data>       <variable name="user" type="com.example.User"/>    </data>    <!-- ... rest of layout here --></layout>

对象的属性写在view中

<TextView    android:id="@+id/tvFullName"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text='@{user.getFirstName + " " + user.getLastName}' />

给user赋值bind view

public class MainActivity extends AppCompatActivity {    private ActivityMainBinding binding;//    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        // Inflate the `activity_main` layout        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);        // Create or access the data to bind        User user = new User("Sarah", "Gibbons");        // Attach the user to the binding        binding.setUser(user);    }}

到这里,运行app,你会发现数据绑定在了视图上了.

主要性能

1. 零反射2. findViewById需要遍历整个ViewGroup,现在之需要做一次3. 使用位标记来检验更新4. 数据改变在下一次批量更新才会触发5. 缓存表达式:      a ? (b ? c : d) : e

表达式 - 例子 - 最佳实践

Margin @dimen + @dimenandroid:text = "@{String.valueOf(index + 1)}"visibility = "@{age < 13 ? View.GONE : View.VISIBle}"transitionName = '@{"image_" + id}'{  1.结合ViewModel使用  2.保持表达式简洁简单}

自动空指针检查,避免空指针

{user.name} -> null{user.age} -> 0

github:
https://github.com/chenxinsi/DataBinding