文本框未触发 PropertyChanged 事件

Question

我正在努力弄清楚为什么当我在文本框中输入文本并离开控件时没有触发 propertychanged 事件或 lostfocus 事件。

我正在构建一个通用 Windows 平台应用程序。

我知道我在做一些迟钝的事情，但我只是没有看到。

有什么建议吗？

XAML：

<Page
    x:Class="xxx.Client.FormPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:viewModels="using:xxx.xxx.ViewModels"
    Background="LightBlue"
    mc:Ignorable="d">

    <Page.Resources>
        <Style x:Key="TextBoxStyle" TargetType="TextBox">
            <Setter Property="HorizontalAlignment" Value="Stretch" />
            <Setter Property="TextAlignment" Value="Center" />
        </Style>
    </Page.Resources>

    <Page.DataContext>
        <viewModels:FormViewModel />
    </Page.DataContext>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto" />
            <RowDefinition Height="auto" />
            <RowDefinition Height="auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="auto" />
        </Grid.RowDefinitions>

        <TextBox Grid.Row="0" Text="{Binding InstructorNameInput}" Style="{StaticResource TextBoxStyle}" 
                 PlaceholderText="Instructor Name" />

        <TextBox Grid.Row="1" Text="{Binding InstructorIdInput}" Style="{StaticResource TextBoxStyle}"
                 PlaceholderText="Instructor Id" />

        <TextBox Grid.Row="2" Text="{Binding CourseInput}" Style="{StaticResource TextBoxStyle}"
                 PlaceholderText="Course" />

        <Button Grid.Row="4" Content="Accept" Command="{Binding Submit}" 
                HorizontalAlignment="Stretch"
                Foreground="Black" />
    </Grid>
</Page>

视图模型：

public partial class FormViewModel : ViewModelBase
    {
        public FormViewModel()
        {
            InstructorName = new RequiredField("Instructor's Name:");
            InstructorId = new RequiredField("Instructor's Employee#:");
            Course = new RequiredField("Course:");

            var courses = CourseFactory.Produce();
            var administration = new Administration(courses, null);
            Submit = new DelegateCommand(_=> OnSubmit(), CanSubmit);
        }

        string _instructorNameInput = null;
        public string InstructorNameInput
        {
            get { return _instructorNameInput; }
            set
            {
                if (_instructorNameInput != value)
                {
                    _instructorNameInput = value;
                    OnNotifyPropertyChanged();
                }
            }
        }

        string instructorIdInput = null;
        public string InstructorIdInput
        {
            get { return instructorIdInput; }
            set
            {
                if (instructorIdInput != value)
                {
                    instructorIdInput = value;
                    OnNotifyPropertyChanged();
                }
            }
        }

        string courseInput = null;
        public string CourseInput
        {
            get { return courseInput; }
            set
            {
                if (courseInput != value)
                {
                    courseInput = value;
                    OnNotifyPropertyChanged();
                }
            }
        }

        public RequiredField InstructorName { get; }
        public RequiredField InstructorId { get; }
        public RequiredField Course { get; }

        public ObservableCollection<RequiredField> RequiredFields { get; } = new ObservableCollection<RequiredField>();
    }

ViewModel.internal：

public partial class FormViewModel
    {
        static void OnSubmit()
        {
            var adminsistration = new Administration();
        }

        bool CanSubmit(object obj) => !GetUnsatisfied().Any();

        IEnumerable<RequiredField> GetUnsatisfied()
        {
            if (string.IsNullOrEmpty(InstructorIdInput))
            {
                RequiredFields.Add(InstructorId);
            }
            else
            {
                var result = 0;
                var isNumeric = int.TryParse(InstructorIdInput, out result);

                if (!isNumeric)
                {
                    RequiredFields.Add(new RequiredField(InstructorId.About, "Instructor ID must be numeric"));
                }
            }

            if (string.IsNullOrEmpty(InstructorNameInput))
            {
                RequiredFields.Add(InstructorName);
            }

            if (string.IsNullOrEmpty(CourseInput))
            {
                RequiredFields.Add(Course);
            }

            return RequiredFields;
        }
    }

Answer 1

UWP的默认绑定模式as MSDN says:

默认为 OneWay。

将其设置为 TwoWay：

<TextBox Grid.Row="0" Text="{Binding InstructorNameInput, Mode=TwoWay}" .../>