WPF : Refresh / Update control on Window load

Question

I want to display time in the Label. The label contents needs to be refreshed automatically as the window is loaded.

I have a simple WPF Window with a Label control in it. As illustrated here

<Window x:Class="shoes.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <Label Margin="12" Name="lblSeconds"></Label>
        <Button Margin="68,22,135,0" Name="button1" Height="24" VerticalAlignment="Top" Click="button1_Click">Button</Button>
    </Grid>
</Window>

I have looked at the code available here : http://geekswithblogs.net/NewThingsILearned/archive/2008/08/25/refresh--update-wpf-controls.aspx

And I modified to fit this way :

public partial class Window1 : Window
{
    private static Action EmptyDelegate = delegate() { };

    public Window1()
    {
        InitializeComponent();

    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        if (IsLoaded)
        {
            LoopingMethod();
        }
    }

    private void LoopingMethod()
    {
        while(true)
        {
            lblSeconds.Content = DateTime.Now.ToLongTimeString();
            lblSeconds.Refresh();
            Thread.Sleep(10);
        }
    }
}
public static class ExtensionMethods
{

    private static Action EmptyDelegate = delegate() { };


    public static void Refresh(this UIElement uiElement)
    {
        uiElement.Dispatcher.Invoke(DispatcherPriority.Render, EmptyDelegate);
    }
}

I have discovered the code works pretty well when it is triggered through a button_Click event. I have tried to get the code to run through a Window_Loaded event like this but in vain. The window content is never displayed.

What I can do to get the label updated automatically when the window is loaded?

Solution 1

Which is perfectly normal, because the OnLoad handler stays in an infinite loop. That loop is on the UI thread, so the Window never shows.

First of all: wrap your loop in a Backgroundworker so that it runs on a separate thread.

I'd also factor out the looping code into a separate object implementing INotifyPropertyChanged which exposes a property with the time (string), have that property raise the PropertyChanged event when it changes (through the loop). You'd still need to do this on a seperate thread of course (eg using BackgroundWorker). Use a Binding to bind your specialized object to the label.

Another tactic would employ a Timer which does a callback at regular intervals, and you can update the label there.

Solution 2

Instead of using an infinite loop use a DispatcherTimer