Andriod --- JetPack ：BaseObservable 与 ObservableField 双向绑定

Andriod — JetPack ：初识 JetPack

Andriod — JetPack ：LifeCycle 的诞生

Andriod — JetPack ：ViewModel 的诞生

Andriod — JetPack ：BaseObservable 与 ObservableField 双向绑定

Andriod — JetPack ：DataBinding + LiveData +ViewModel 简单实例

Andriod — JetPack ：Room 增删改查

Andriod — JetPack ：Room + ViewModel + LiveData 增删改查实例

Andriod — JetPack ：LiveData setValue 和 postValue 的区别

一、什么叫单向绑定与双向绑定

单向绑定：对象变化的时候 TextView 自动更新 双向绑定：对象变化的时候 EditView 自动更新。EditText 变化的时候对象的值也发生变化。

二、BaseObservable 双向绑定代码实例

build.gradle

android { compileSdkVersion 29 buildToolsVersion "30.0.3" dataBinding { enabled = true } } 

MainActivity.java

import androidx.appcompat.app.AppCompatActivity; import androidx.databinding.DataBindingUtil; import androidx.databinding.ViewDataBinding; import android.os.Bundle; import com.example.baseobservable.databinding.ActivityMainBinding; public class MainActivity extends AppCompatActivity { @Override
    protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ActivityMainBinding activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main); activityMainBinding.setUserViewModel(new UserViewModel()); } } 

activity_main.xml

<?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> <variable name="userViewModel" type="com.example.baseobservable.UserViewModel" /> </data> <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <EditText
            android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@={userViewModel.userName}" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintLeft_toLeftOf="parent" app:layout_constraintRight_toRightOf="parent" app:layout_constraintTop_toTopOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout> </layout> 

User.java

package com.example.baseobservable; public class User { public String userName; public User(String userName) { this.userName = userName; } } 

UserViewModel.java

package com.example.baseobservable; import android.util.Log; import androidx.databinding.BaseObservable; import androidx.databinding.Bindable; // 并不是真正的 ViewModel public class UserViewModel extends BaseObservable { private User user; public UserViewModel() { this.user = new User("Jack"); } /*
     * 用 Bindable 进行绑定
     * 只要对象发生变化 EditText 就会发生变化
     */ @Bindable public String getUserName() { return user.userName; } // EditText 中的内容发生变化就会调用 setUserName public void setUserName(String userName) { if(userName != null && !userName.equals(user.userName)) { user.userName = userName; Log.d("liang", userName); notifyPropertyChanged(BR.userName); // 通知属性发生变化 , build 之后自动生成 } } } 

结果：

三、ObservableField 双向绑定代码实例

需要修改的文件： UserViewModel.java

package com.example.baseobservable; import android.util.Log; import androidx.databinding.BaseObservable; import androidx.databinding.Bindable; import androidx.databinding.ObservableField; // 并不是真正的 ViewModel public class UserViewModel { private ObservableField<User> userObservableField; public UserViewModel() { User user = new User("Jack"); userObservableField = new ObservableField<>(); userObservableField.set(user); // userObservableField 与 user 关联起来 } public String getUserName() { return userObservableField.get().userName; } public void setUserName(String userName) { Log.d("liang", userName); userObservableField.get().userName = userName; } }