Question

我正在研究新的体系结构ViewModel组件，打算逐个活动地将我的应用迁移到该组件。我的应用程序已使用数据绑定，并具有一些模型对象作为BaseObservable。当前，我有一个活动进行API调用，如果调用失败，我将还原UI中的更改。我为此使用双向绑定。现在，我为该活动创建一个ViewModel类，并将一些业务逻辑和API调用移至该活动。完成此操作后，失败的API调用上的还原序列将不再更新UI。我看到值更改到达了我的BaseObservable模型，该模型调用notifyChanged方法，但是该模型具有mCallbacks == null，因此在模型更改后没有任何侦听器来更新UI。这是碎片：

OnCreate的活动部分

this.dataBinding = DataBindingUtil.setContentView(this, R.layout.activity_settings)
val viewModel = AppSettingsViewModel(this.application)
this.dataBinding.viewModel = viewModel
this.dataBinding.setLifecycleOwner(this)
this.lifecycle.addObserver(this.dataBinding.viewModel!!)
this.dataBinding.context = this

部分布局：

<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto">
   <data>
      <variable name="context" type="letstwinkle.com.twinkle.AppSettingsActivity" />
      <variable name="viewModel" type="letstwinkle.com.twinkle.viewmodel.AppSettingsViewModel"/>
      ...imports...
   </data>

   <androidx.drawerlayout.widget.DrawerLayout
      android:id="@+id/drawer"
      android:layout_width="match_parent" android:layout_height="match_parent"
      >

   ...more nested views...
                  <Switch
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
                     android:layout_marginTop="15dp"
                     android:layout_marginStart="12dp"
                     android:text="@string/new_matches"
                     android:checked="@={viewModel.settings.pnMatches}"
                     android:textColor="@color/settingsItem"
                     android:onClick="@{(v) -> viewModel.toggleNewMatches(((Checkable)v).isChecked)}"
                     android:enabled="@{viewModel.settings != null}"
                     />
</layout>

最后是ViewModel / SettingsModel

internal class AppSettingsViewModel(app: Application) : AndroidViewModel(app), VolleyErrorObservable,
    ResponseHandler<SubmitResult>, LifecycleObserver
{
    var settings: SettingsModel? = null
    val account = User.account
    val demoMessageText = MutableLiveData<String>()
    override val volleyError = MutableLiveData<VolleyError>()

    fun toggleNewMatches(newValue: Boolean) {
        this.twinkleApplication.trackEvent("click:togglesetting", "App Settings Toggle Setting",
                                           Bundle().apply { putString("setting", "pn_match") })
        updateBoolSetting("pn_match", newValue) { set, b -> set.pnMatches = b}
    }

    private fun updateBoolSetting(setting: String, newValue: Boolean, reverter: (SettingsModel, Boolean) -> Unit) {
        val obj = this.settings!!.jsonForSetting(setting, newValue)
        val suh = SettingsUpdateHandler(this.settings!!, setting == "mp_enabled")
            { settings -> reverter(settings, !newValue) }
        APIClient.updateSettings(obj, suh)
    }
    ...
}

private class SettingsUpdateHandler(val settings: SettingsModel,
                                    val isMPEnabled: Boolean = false,
                                    val revertFun: (SettingsModel) -> Unit)
    : ResponseHandler<SubmitResult>
{
    override fun onErrorResponse(error: VolleyError) {
        revertFun(settings)
        if (weakToast?.get()?.view?.isShown == true) {
            weakToast?.get()?.cancel()
        }
        val toast = Toast.makeText(TwinkleApplication.instance,
                                   R.string.failed_save_settings, Toast.LENGTH_LONG)
        ...
    }
    override fun onResponse(response: SubmitResult) {
        ...
    }

}

@Table(database = Database::class, useBooleanGetterSetters = false)
internal class SettingsModel() : BaseObservable(), Model {
    @NotNull @Column @get:Bindable var pnMatches: Boolean = false
        set(value) {
            Log.d("SettingsModel", "set pnMatches: value=$value, field=$field")
            val changed = field != value
            field = value
            notifyIfChanged(BR.pnMatches, changed)
        }
    ...
    private inline fun notifyIfChanged(field: Int, changed: Boolean) {
        if (changed)
            notifyPropertyChanged(field)
    }
}

我希望在将viewModel.settings.pnMatches的值改回时将Switch切换回去，但是不会。

Answer 1

我在数据绑定文档页面之一上找到了答案，其中包括关于ViewModel / LiveData用法的讨论：ViewModel需要实现Observable本身，并在不是LiveData的Observable字段上使用Bindable批注：

internal class AppSettingsViewModel(app: Application) : AndroidViewModel(app), VolleyErrorObservable,
    ResponseHandler<SubmitResult>, NotifiableObservable by BaseNotifiableObservable()
{
    @get:Bindable
    var settings: SettingsModel? = null
.....

NotifiableObservable位是Kotlin惯用语，用于通过委托实现Observable，这是我在网上找到的。

体系结构ViewModel中的BaseObservable字段未添加任何观察者回调

1 个答案: