One 、 Preface

DataBinding yes JetPack Part of , Generally speaking, if and JetPack The effect will be better when used in combination with other parts of , Record it here . As mentioned before, if you want to refresh the data in real time when it changes UI It needs to use Observable Subclasses of , such as ObservableInt. Let's introduce if and LiveData、ViewMode Combined with refresh UI The situation of

Two 、LiveData Use

Here is a function , take LiveData Is bound to UI above , Update the value after a period of time , Refresh it UI

class UserViewModel: ViewModel() {
    
    val userName = MutableLiveData<String>(" The default value is ")
}

class MainActivity : AppCompatActivity() {
    
    private val binding: ActivityMainBinding by lazy {
    
        ActivityMainBinding.inflate(layoutInflater)
    }
    override fun onCreate(savedInstanceState: Bundle?) {
    
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
        val viewModel = ViewModelProvider(this).get(UserViewModel::class.java)
        binding.viewmodel = viewModel
        binding.lifecycleOwner = this
        binding.root.postDelayed({
    
            viewModel.userName.value  = " Update value "
        },1000)
    }
}

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:bind="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable name="viewmodel" type="com.example.myapplication.UserViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity">
        <TextView android:id="@+id/update_content" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="20dp" android:text="@{viewmodel.userName}" app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintBottom_toBottomOf="parent" tools:text="value" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

3、 ... and 、ViewMode Use

The following are from official documents

You can use the implementation Observable Of ViewModel Components , Send data change notification to other application components , This is with the use of LiveData Objects behave in a similar way .

In some cases , You may prefer to implement Observable Interface ViewModel Components , Instead of using LiveData object , Even if this will lose the right LiveData The lifecycle management function of does not affect . Use to implement Observable Of ViewModel Component allows you to better control the binding adapter in your application . for example , This pattern gives you better control over the notifications that are issued when data changes , You can also specify custom methods to set property values in bidirectional data binding .

To achieve observable ViewModel Components , You must create one from ViewModel Class inherits and implements Observable The class of the interface . You can use addOnPropertyChangedCallback() and removeOnPropertyChangedCallback() Method provides custom logic for observers to subscribe to or unsubscribe from notifications . You can also notifyPropertyChanged() Method provides custom logic that runs when a property is changed . The following code example shows how to implement an observable ViewModel：

This method and custom implementation Observable Classes are similar , Examples are as follows

ViewModel

class ObservableUserModel : ViewModel(), Observable {
    
    private val callbacks: PropertyChangeRegistry = PropertyChangeRegistry()

    @Bindable
     var name = " The default value is "

    fun updateName(newName : String){
    
        name = newName
        notifyPropertyChanged(BR.name)
    }

    override fun addOnPropertyChangedCallback(
        callback: Observable.OnPropertyChangedCallback) {
    
        callbacks.add(callback)
    }

    override fun removeOnPropertyChangedCallback(
        callback: Observable.OnPropertyChangedCallback) {
    
        callbacks.remove(callback)
    }

    /** * Notifies observers that all properties of this instance have changed. */
    fun notifyChange() {
    
        callbacks.notifyCallbacks(this, 0, null)
    }

    /** * Notifies observers that a specific property has changed. The getter for the * property that changes should be marked with the @Bindable annotation to * generate a field in the BR class to be used as the fieldId parameter. * * @param fieldId The generated BR id for the Bindable field. */
    fun notifyPropertyChanged(fieldId: Int) {
    
        callbacks.notifyCallbacks(this, fieldId, null)
    }
}

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:bind="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable name="observableModel" type="com.example.myapplication.ObservableUserModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity">
        <TextView android:id="@+id/update_content" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="20dp" android:text="@{observableModel.name}" android:paddingStart="10dp" app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintBottom_toBottomOf="parent" tools:text="value" />

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

MainActivity.kt

class MainActivity : AppCompatActivity() {
    
    private val binding: ActivityMainBinding by lazy {
    
        ActivityMainBinding.inflate(layoutInflater)
    }
    override fun onCreate(savedInstanceState: Bundle?) {
    
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
        // Obtain ViewModel from ViewModelProviders
        val viewModel = ViewModelProvider(this).get(ObservableUserModel::class.java)
        binding.observableModel = viewModel
        binding.root.postDelayed({
    
            viewModel.updateName(" The new value --")
        },1000)
    }
}

Four 、 Reference link

1. Binding layout views to architecture components  |  Android developer  |  Android Developers