UWP 应用程序未更新视图

Question

一个简单的练习：在 UWP 应用的文本块中显示当前时间。我正在使用 MVVMlight 和 PropertyChanged.Fody.

作为这个例子的基础，我使用这个 article and the MVVMlight / Fody implementation from here: Article 2

我有一个 MainViewModel。在这里，我正在创建 DateTimeModel class 的一个实例，如果引发属性更改事件（工作），我已经添加了调试输出。

using System.Diagnostics;
using GalaSoft.MvvmLight;
using Logic.Ui.Models.DateTime;
using PropertyChanged;

namespace Logic.Ui
{
    public class MainViewModel : ViewModelBase, INotifyPropertyChanged
    {

        public DateTimeModel DateTimeModel;

        [DependsOn(nameof(DateTimeModel))]
        public DateTime CurrentDateTime => DateTimeModel.CurrentDateTime;

        public MainViewModel()
        {
            DateTimeModel = new DateTimeModel();

            DateTimeModel.PropertyChanged += (s, e) =>
            {
                Debug.WriteLine("DateTime PropertyChanged");
            };
        }

        #region Events

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion

    }
}

还有一个 DateTimeModel class，我在其中使用 ThreadPoolTimer 更新时间：

using System;
using System.ComponentModel;
using System.Diagnostics;
using Windows.System.Threading;
using Windows.UI.Core;

namespace Logic.Ui.Models.DateTime
{

    public class DateTimeModel : INotifyPropertyChanged
    {
        private ThreadPoolTimer _clockTimer;

        public System.DateTime CurrentDateTime { get; set; }
        
        public DateTimeModel()
        {
            _clockTimer = ThreadPoolTimer.CreatePeriodicTimer(ClockTimerTickAsync, TimeSpan.FromMilliseconds(1000));
        }

        private async void ClockTimerTickAsync(ThreadPoolTimer timer)
        {
            await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
            {
                CurrentDateTime = System.DateTime.Now;
                Debug.WriteLine("Time updated");
            });

        }

        #region Events

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }
}

XAML 代码如下所示：

<Page
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MirrorV2.Ui.Raspberry"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    x:Class="MirrorV2.Ui.Raspberry.MainPage"
    mc:Ignorable="d"
    DataContext="{Binding Main, Source={StaticResource Locator}}">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

        <TextBlock Text="{Binding CurrentDateTime}"/>
        
    </Grid>
</Page>

这里的问题是 UI 没有更新，而正在引发属性Changed 事件。我在这里缺少什么？

编辑：如果我使用 CurrentDateTime 作为标准属性:

public DateTime CurrentDateTime { get; set; }

并在绑定起作用的构造函数中分配当前 DateTime。

CurrentDateTime = System.DateTime.Now;

Answer 1

每当引发 DateTimeModel 的 PropertyChanged 事件时，引发绑定到 MainViewModel 的 CurrentDateTime 的 PropertyChanged 事件：

public class MainViewModel : ViewModelBase, INotifyPropertyChanged
{
    public DateTimeModel DateTimeModel;

    [DependsOn(nameof(DateTimeModel))]
    public DateTime CurrentDateTime => DateTimeModel.CurrentDateTime;

    public MainViewModel()
    {
        DateTimeModel = new DateTimeModel();

        DateTimeModel.PropertyChanged += (s, e) =>
        {
            Debug.WriteLine("DateTime PropertyChanged");
            this.RaisePropertyChanged(nameof(CurrentDateTime)); //<---
        };
    }

    #region Events
    public event PropertyChangedEventHandler PropertyChanged;
    #endregion
}

或者您可以 DateTimeModel 属性在 MainViewModel class:

public DateTimeModel DateTimeModel { get; private set; }

...并直接绑定到 DateTimeModel 的 CurrentDateTime 属性:

<TextBlock Text="{Binding DateTimeModel.CurrentDateTime}"/>

Answer 2

您面临的问题是 MainViewModel.CurrentDateTime 仅在您分配 MainViewModel.DateTimeModel 时收到通知，而不是在 DateTimeModel 的属性更改时收到通知。

This is a known Fody limitation and a guy here found a walkaround 允许您通知 sub属性更改，如下所示：

public class MainViewModel : ViewModelBase, INotifyPropertyChanged
{

    // ... snip ...

    [DependsOn(nameof(DateTimeModel))]
    [DependsOn("DateTimeModel.CurrentDateTime")]
    public DateTime CurrentDateTime => DateTimeModel.CurrentDateTime;
}

但我认为删除 MainViewModel.CurrentDateTime 并直接绑定到 MainViewModel.DateTimeModel 更优雅

<TextBlock Text="{Binding DateTimeModel.CurrentDateTime}"/>

这需要按照的建议将 DateTimeModel 更改为属性:

public DateTimeModel DateTimeModel { get; }

UWP 应用程序未更新视图

UWP app not updating view

c#

mvvm-light

fody-propertychanged

uwp