android - 当 LiveData 在 Android Studio 中的双向数据绑定(bind)中更改时，如何重置 LiveData？

Question

在 layout_detail.xml 中 EditText 使用双向数据绑定(bind)和 Button 使用单向数据绑定(bind)
我希望 Button 将在 aDetailViewModel.aMVoice.name 时启用被改变。
当 EditText 的内容发生变化时，aMVoice 的值在 DetailViewModel也将被更改，我想我可以重置 isChanged 的值，但我不知道怎么办？你可以告诉我吗？
layout_detail.xml

<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>
        <import type="android.view.View" />
        <variable name="aDetailViewModel"
            type="info.dodata.voicerecorder.viewcontrol.DetailViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <EditText
            android:id="@+id/eTName"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPersonName"
            android:text="@={aDetailViewModel.aMVoice.name}" />

        <Button
            android:id="@+id/btnSave"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:enabled="@{aDetailViewModel.isChanged}"
            android:text="Save" />

    </LinearLayout>

</layout>

代码

class DetailViewModel(private val mDBVoiceRepository: DBVoiceRepository, private val voiceId:Int) : ViewModel() {

   val aMVoice=mDBVoiceRepository.getVoiceById(voiceId)     //I hope to reset isChanged when aMVoice is changed

   val isChanged: LiveData<Boolean> = MutableLiveData<Boolean>(false)    
}
  

class DBVoiceRepository private constructor(private val mDBVoiceDao: DBVoiceDao){
    fun getVoiceById(id:Int)=mDBVoiceDao.getVoiceById(id)
}

@Dao
interface DBVoiceDao{      
   @Query("SELECT * FROM voice_table where id=:id")
   fun getVoiceById(id:Int):LiveData<MVoice>
}

@Entity(tableName = "voice_table", indices = [Index("createdDate")])
data class MVoice(
    @PrimaryKey (autoGenerate = true) @ColumnInfo(name = "id") var id: Int = 0,
    var name:          String = "",
    var path:          String = "",  
)

Answer 1

由于您想找出多个属性的值变化，我们应该将每个属性分隔在一个特定的 LiveData 中。通过 map转变。这些新的LiveData s 起到双向绑定(bind)的作用。
最后，要集成更改，最好的方法是使用 MediatorLiveData由每次更改触发，然后检查值。因此，从 DB 检查初始值的相等性就足够了。从 View 中接收到的值。

class DetailViewModel(...) {

    private val aMVoice = mDBVoiceRepository.getVoiceById(voiceId)

    val voiceName = aMVoice.map { it.name } as MutableLiveData<String>
    val voicePath = aMVoice.map { it.path } as MutableLiveData<String>
    // ... (similar for more attributes)

    val isChanged = MediatorLiveData<Boolean>().apply {
        addSource(voiceName) { postValue(currentMVoice != aMVoice.value) }
        addSource(voicePath) { postValue(currentMVoice != aMVoice.value) }
        // ... (similar for more attributes)
    }

    // it collects current values delivered from views as a `MVoice` object.
    private val currentMVoice: MVoice?
        get() = aMVoice.value?.copy(
            name = voiceName.value ?: "",
            path = voicePath.value ?: "",
            // ... (similar for more attributes)
        )
}

然后使用 voiceName , voicePath等在布局中:

<EditText
    android:id="@+id/eTName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="textPersonName"
    android:text="@={aDetailViewModel.voiceName}" />

<EditText
    android:id="@+id/eTPath"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="text"
    android:text="@={aDetailViewModel.voicePath}" />

// ...

使用 map改造别忘了加 lifecycle-livedata-ktx build.gradle 中的依赖项如果你以前没有。

implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.2.0'