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?

Answer 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.