Show current time WPF

Question

The only way to show current time updating regularly I found is to use timer. Of course, I can implement INotifyPropertyChanged and some special property to be

Answer 1

WPF is a static markup language. As far as I am aware there is not a mechanism available in pure XAML to provide the functionally you are looking for.

If you want to avoid using a timer directly you can abstract it away using Tasks.

MainWindow XAML:

<Window x:Class="AsyncTimer.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:AsyncTimer"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Label Content="{Binding CurrentTime}"></Label>
    </Grid>
</Window>

Code behind:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        DataContext = new CurrentTimeViewModel();
    }
}

public class CurrentTimeViewModel : INotifyPropertyChanged
{
    private string _currentTime;

    public CurrentTimeViewModel()
    {
        UpdateTime();
    }

    private async void UpdateTime()
    {
        CurrentTime = DateTime.Now.ToString("G");
        await Task.Delay(1000);
        UpdateTime();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public string CurrentTime
    {
        get { return _currentTime; }
        set { _currentTime = value; OnPropertyChanged(); }
    }
}

This is probably one of the more succinct and certainly as "Modern" WPF you are going to get.

Answer 2

Here is a little code sample that works without a timer:

public DateTime CurrentTime
{
    get => DateTime.Now;
}

public CurrentViewModelTime(object sender, RoutedEventArgs e)
{
    _ = Update(); // calling an async function we do not want to await
}

private async Task Update()
{
    while (true)
    {
        await Task.Delay(100);
        OnPropertyChanged(nameof(CurrentTime)));
    }
}

Of course, this Update() function never returns, but it does its loop on a threadpool thread and does not even block any thread for long.

You can perfectly also implement this in the window directly without a viewmodel.

Answer 3

Using Task.Delay can produce an high CPU usage!

In the XAML code write this:

<Label Name="LiveTimeLabel" Content="%TIME%" HorizontalAlignment="Left" Margin="557,248,0,0" VerticalAlignment="Top" Height="55" Width="186" FontSize="36" FontWeight="Bold" Foreground="Red" />

Next in the xaml.cs write this:

[...]
public MainWindow()
{
    InitializeComponent();
    DispatcherTimer LiveTime = new DispatcherTimer();
    LiveTime.Interval = TimeSpan.FromSeconds(1);
    LiveTime.Tick += timer_Tick;
    LiveTime.Start();
}

void timer_Tick(object sender, EventArgs e)
{
    LiveTimeLabel.Content = DateTime.Now.ToString("HH:mm:ss");
}
[...]