本机绑定不适用于AutoCompleteTextView

Question

我要做的是：在this article中所示的android（原生）小部件Text上为AutoCompleteTextView属性分配双向绑定。

它失败的地方尽管如此，完全相同的方法适用于Switch，但EditText和AutoCompleteTextView都失败了。我尝试在绑定表达式中使用TextChanged，AfterTextChanged和FocusChange作为UpdateSourceEventName的事件。每个都失败了。在TextChanged的情况下，值会反向更新，因为光标位置会一直恢复到起始点，而在FocusChange中，事件似乎根本不会被触发。

重新创建问题的示例代码：

XAML

<ContentPage 
    xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    xmlns:local="clr-namespace:NativeViewTest"
    xmlns:androidWidget="clr-namespace:Android.Widget;assembly=Mono.Android;targetPlatform=Android"
    xmlns:formsAndroid="clr-namespace:Xamarin.Forms;assembly=Xamarin.Forms.Platform.Android;targetPlatform=Android"
    x:Name="_parent"
    x:Class="NativeViewTest.NativeViewTestPage">

    <StackLayout Margin="10">

        <Label TextColor="Green" Text="Switch + CheckedChange: Binding works as expected." />
        <androidWidget:Switch x:Arguments="{x:Static formsAndroid:Forms.Context}" Text="Is Switch On?"
            Checked="{Binding Path=IsSwitchOn, Source={x:Reference _parent}, Mode=TwoWay, UpdateSourceEventName=CheckedChange}" />
        <Label Text="{Binding Path=IsSwitchOn, StringFormat='IsSwitchOn: {0}', Source={x:Reference _parent}" />

        <Label TextColor="Navy" Text="AutoCompleteTextView + TextChanged: Value is updated in reverse." />
        <androidWidget:AutoCompleteTextView x:Arguments="{x:Static formsAndroid:Forms.Context}"
            Text="{Binding Path=TextChangedText, Source={x:Reference _parent}, Mode=TwoWay, UpdateSourceEventName=TextChanged}" />
        <Label Text="{Binding Path=TextChangedText, StringFormat='TextChangedText: {0}', Source={x:Reference _parent}" />

        <Label TextColor="Red" Text="AutoCompleteTextView + FocusChange: Value is never updated." />
        <androidWidget:AutoCompleteTextView x:Arguments="{x:Static formsAndroid:Forms.Context}"
            Text="{Binding Path=LostFocusText, Source={x:Reference _parent}, Mode=TwoWay, UpdateSourceEventName=FocusChange}" />
        <Label Text="{Binding Path=LostFocusText, StringFormat='LostFocusText: {0}', Source={x:Reference _parent}" />

        <Label TextColor="Navy" Text="AutoCompleteTextView + AfterTextChanged: Same issue as text-changed" />
        <androidWidget:AutoCompleteTextView x:Arguments="{x:Static formsAndroid:Forms.Context}"
            Text="{Binding Path=AfterTextChangedText, Source={x:Reference _parent}, Mode=TwoWay, UpdateSourceEventName=AfterTextChanged}" />
        <Label Text="{Binding Path=AfterTextChangedText, StringFormat='AfterTextChangedText: {0}', Source={x:Reference _parent}" />

        <Button Text="Update" />

    </StackLayout>

</ContentPage>

代码隐藏

public partial class NativeViewTestPage : ContentPage
{
    public NativeViewTestPage()
    {
        InitializeComponent();
    }

    string _afterTextChanged;
    public string AfterTextChangedText
    {
        get { return _afterTextChanged; }
        set { 
            _afterTextChanged = value; 
            OnPropertyChanged(nameof(AfterTextChangedText)); 
        }
    }

    string _textChangedText = "initial value";
    public string TextChangedText
    {
        get { return _textChangedText; }
        set
        {
            _textChangedText = value;
            OnPropertyChanged(nameof(TextChangedText));
        }
    }

    string _lostFocusText;
    public string LostFocusText
    {
        get { return _lostFocusText; }
        set
        {
            _lostFocusText = value;
            OnPropertyChanged(nameof(LostFocusText));
        }
    }

    bool _isSwitchOn = false;
    public bool IsSwitchOn
    {
        get { return _isSwitchOn; }
        set
        {
            _isSwitchOn = value;
            OnPropertyChanged(nameof(IsSwitchOn));
        }
    }
}

编辑 - 1

我尝试将绑定模式更改为OneWayToSource，假设可以解决游标问题 - 但仍会导致完全相同的问题。