WPF: What is between the Initialized and Loaded event?

Question

I want to run some code when the Window or Control is first displayed. I can't use Loaded because that can fire more than once. I can't use Initialized because that is done by the constructor.

Is there an event somewhere between?

Answer 1

Unfortunately there is no such event. You can use a boolean in the Loaded Method to make sure your stuff only fires once -

if(!IsSetUp)
{
   MySetUpFunction();
   IsSetUp = true;
}

Check out the WPF Windows lifetime events here:

http://msdn.microsoft.com/en-us/library/ms748948.aspx#Window_Lifetime_Events

_{(source: microsoft.com)}

Answer 2

Alternatively to storing a boolean flag, you can use an extension method and delegate wrapping to fake Loaded only firing once.

public static void OnLoadedOnce(
    this UserControl control,
    RoutedEventHandler onLoaded)
{
    if (control == null || onLoaded == null)
    {
        throw new ArgumentNullException();
    }

    RoutedEventHandler wrappedOnLoaded = null;
    wrappedOnLoaded = delegate(object sender, RoutedEventArgs e)
    {
        control.Loaded -= wrappedOnLoaded;
        onLoaded(sender, e);
    };
    control.Loaded += wrappedOnLoaded;
}

...

class MyControl : UserControl
{
    public MyControl()
    { 
        InitializeComponent();
        this.OnLoadedOnce(this.OnControlLoaded /* or delegate {...} */);
    }

    private void OnControlLoaded(object sender, RoutedEventArgs e)
    {
    }
}

Answer 3

If you don't want to use the boolean method of doing things, then you can create a method and subscribe to the Loaded event with it, then unsubscribe at the end of that method.

Example:

public MyDependencyObject(){
  Loaded += OnLoaded;
}

private void OnLoaded(object sender, EventArgs args){
  DoThings();
  Loaded -= OnLoaded;
}