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WPF MVVM不更新视图

viewmodel binding mvvm wpf c#

Barta · 技术社区 · 10 月前

我正在开发一个需要秒表的应用程序。我想用文本块显示经过的时间。我的问题是,视图没有更新,但我可以使用ICommands。

我在这里分配 DataContext

public partial class ProgressPage : Grid
{
    public ProgressPage(ProjectInfo projectInfo)
    {
        DataContext = new ProgressViewModel(projectInfo);
        InitializeComponent();
    }
}

这是我的 ViewModel

public class ProgressViewModel : INotifyPropertyChanged
{
    private ProjectInfo projectInfo;
    private ICommand _start;
    private DispatcherTimer timer = new()
    {
        Interval = TimeSpan.FromSeconds(1)
    };

    public event PropertyChangedEventHandler? PropertyChanged;

    public ProjectInfo ProjectInfo
    {
        get { return projectInfo; }
        set
        {
            projectInfo = value;
            NotifyPropertyChanged();
        }
    }

    private string elapsedTimeString;

    public string ElapsedTimeString
    {
        get { return elapsedTimeString; }
        set
        {
            elapsedTimeString = value;
            NotifyPropertyChanged();
        }
    }

    public ICommand StartCommand
    {
        get
        {
            _start ??= new RelayCommand(
                    p => true,
                    p => Start());
            return _start;
        }
    }

    private void Start()
    {
        ProjectInfo.CurrentStartedTime = DateTime.Now;
        timer.Start();
    }

    public ProgressViewModel(ProjectInfo projectInfo)
    {
        ProjectInfo = projectInfo;
        timer.Tick += Tick;
    }

    private void Tick(object? sender, EventArgs e)
    {
        ElapsedTimeString = (DateTime.Now - ProjectInfo.CurrentStartedTime).ToString(@"hh\:mm\:ss");
    }

    private void NotifyPropertyChanged([CallerMemberName] string name = null)
    {
        PropertyChanged?.Invoke(null, new PropertyChangedEventArgs(name));
    }
}

这是我的 XAML

<TextBlock Text="{Binding ElapsedTimeString}"
           Style="{StaticResource ProgressText}" />

这是一张捕捉到断点的图片

命令正在工作,计时器正在工作 NotifyPropertyChanged 方法也在工作(name参数也正确),但视图没有更新。

我该怎么解决这个问题?

3 回复 | 直到 10 月前

Sheriff 10 月前

尝试改变” 无效的 “与这在里面 PropertyChanged?.Invoke(null, new PropertyChangedEventArgs(name)); 到 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));

当我更改它并调用start方法时,文本块Text被更新了。

ezechiel 10 月前

也许试着添加

<TextBlock Text="{Binding ElapsedTimeString, UpdateSourceTrigger=PropertyChanged}"
           Style="{StaticResource ProgressText}" />

EldHasp 10 月前

XAML不正确或没有完全反映逻辑。您在开头指定了数据上下文分配片段 DataContext = new ProgressViewModel(projectInfo); ,但在XAML中,您可以从参考资料中获取源代码。这两种方式有点矛盾。

我还怀疑您没有完全正确地设置将TimeSpan转换为字符串的格式。

看看我的实现示例。它基于以下课程: An example of my implementation of base classes (.Net 8): BaseInpc, RelayCommand, RelayCommandAsync, RelayCommand, RelayCommandAsync.

using Simplified;

namespace SOTopics2025.SO.Barta.question79330621
{
    public class Stopwatch : BaseInpc
    {
        public TimeSpan ElapsedTime { get; private set; }
        public DateTime StartTime { get; private set; }

        public bool IsEnabled { get; private set; }
        private readonly Timer timer;

        public Stopwatch()
        {
            timer = new Timer(OnTick);
            StartCommand = new RelayCommand
            (
                () =>
                {
                    if (IsEnabled)
                        return;
                    StartTime = DateTime.Now;
                    IsEnabled = true;
                    ElapsedTime = TimeSpan.Zero;

                    RaisePropertyChanged(string.Empty);
                    StartCommand!.RaiseCanExecuteChanged();
                    StopCommand!.RaiseCanExecuteChanged();

                    timer.Change(10, 10);
                },
                () => !IsEnabled
            );

            StopCommand = new RelayCommand
            (
                () =>
                {
                    if (IsEnabled)
                    {
                        IsEnabled = false;

                        RaisePropertyChanged(string.Empty);
                        StartCommand.RaiseCanExecuteChanged();
                        StopCommand!.RaiseCanExecuteChanged();

                        timer.Change(Timeout.Infinite, Timeout.Infinite);
                    }
                },
                () => IsEnabled
            );
        }

        private void OnTick(object? state)
        {
            ElapsedTime = DateTime.Now - StartTime;
            RaisePropertyChanged(nameof(ElapsedTime));
        }

        public RelayCommand StartCommand { get; }
        public RelayCommand StopCommand { get; }
    }
}

<Window x:Class="SOTopics2025.SO.Barta.question79330621.StopwatchTestWindow"
        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:SOTopics2025.SO.Barta.question79330621"
        mc:Ignorable="d"
        Title="StopwatchTestWindow" Height="250" Width="400">
    <Window.DataContext>
        <local:Stopwatch/>
    </Window.DataContext>
    <UniformGrid Columns="2">
        <TextBlock Text="{Binding StartTime}" VerticalAlignment="Center" HorizontalAlignment="Center">
            <TextBlock.Style>
                <Style TargetType="TextBlock">
                    <Setter Property="Foreground" Value="Red"/>
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding IsEnabled}" Value="True">
                            <Setter Property="Foreground" Value="Green"/>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBlock.Style>
        </TextBlock>
        <TextBlock Text="{Binding ElapsedTime, StringFormat=hh\\:mm\\:ss\\.ff}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
        <Button Content="Start" Padding="15 5" VerticalAlignment="Center" HorizontalAlignment="Center" Command="{Binding StartCommand, Mode=OneWay}"/>
        <Button Content="Stop" Padding="15 5" VerticalAlignment="Center" HorizontalAlignment="Center" Command="{Binding StopCommand, Mode=OneWay}"/>
    </UniformGrid>
</Window>