wpf - 在WPF应用程序屏幕上看不到日期时间文本

Question

我正在尝试编写一个简单的MVVM应用程序。该示例的期望是在屏幕上显示时间。
xaml设计师曾经在设计师中展示过一次时间


但是当我运行该应用程序时，我根本没有在屏幕上看到时间。
您能帮我找到问题所在吗？
我在这里附加代码。

MainWindow.xaml

    <Window x:Class="WPFDigitalClock.MainWindow"
        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:local="clr-namespace:WPFDigitalClock"        
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:ClockVM/>
    </Window.DataContext>
    <Grid>
        <StackPanel>
            <TextBlock Foreground="White" Background="Black" FontSize="30" TextAlignment="Center" Text="{Binding Path=DisplayTime}"/>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs

using System.Windows;

namespace WPFDigitalClock
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();            
        }
    }
}

ClockVM.cs

using System;
using System.ComponentModel;
using System.Windows.Threading;

namespace WPFDigitalClock
{
    class ClockVM : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private ClockModel clockModel;       

        DispatcherTimer Timer = new DispatcherTimer();
        public string DisplayTime { get; set; }

        public ClockVM()
        {
            clockModel = new ClockModel();
            DisplayTime = "";
            Timer.Interval = new TimeSpan(0, 0, 1);
            Timer.Tick += new EventHandler(Timer_Click);
            Timer.Start();

        }

        private void Timer_Click(object sender, EventArgs e)
        {
            DisplayTime = clockModel.Hour + ":" + clockModel.Minute + ":" + clockModel.Second;
            if (PropertyChanged != null)
            {
                PropertyChanged(sender, new PropertyChangedEventArgs("DisplayTime"));
            }
        }
    }
}

ClockModel.cs

using System;

namespace WPFDigitalClock
{
    class ClockModel
    {
        public string Hour
        {
            get { return DateTime.Now.Hour.ToString(); }            
        }

        public string Minute
        {
            get { return DateTime.Now.Minute.ToString(); }
        }

        public string Second
        {
            get { return DateTime.Now.Second.ToString(); }
        }
    }
}

Answer 1

问题在于您如何引发了属性DisplayTime的更改。在DispatcherTimer.Tick处理程序中使用以下代码:

 private void Timer_Click(object sender, EventArgs e)
    {
        DisplayTime = clockModel.Hour + ":" + clockModel.Minute + ":" + clockModel.Second;
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs("DisplayTime"));
        }
    }

You have passed the sender object as argument in PropertyChanged method. It expect owner class of Property DisplayTime in sender argument.