Visual Studio 2013 WPF UserControl RoutedEvent名称已使用？

Question

I have a WPF project in Visual Studio 2013 which contains a custom control I created, containing a custom event. Whenever I drag the control into my MainWindow.xaml file, it will display once in the designer. As soon as I compile my application (which succeeds), the designer will display something like this, showing my control is broken:

In the XAML code (again, only after the first compile), I get this tip:

However, no matter what I change my event name to (say "EggsAndBaconEvent"), it will always break the designer after the first compile.

Visual Studio will try to help me in this window:

Here is my code which is related to creating an event:

public partial class Settings : UserControl {
    ...

    public static RoutedEvent ExpandEvent;

    public Settings() {
        ...

        ExpandEvent = EventManager.RegisterRoutedEvent("Expanded", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(Settings));
    }

    ...

    public event RoutedEventHandler Exapnd {
        add { AddHandler(ExpandEvent, value); }
        remove { RemoveHandler(ExpandEvent, value); }
    }

    private void expanderChanged(object sender, RoutedEventArgs e) {
        ...

        RoutedEventArgs args = new RoutedEventArgs(ExpandEvent);
        RaiseEvent(args);
    }
}

Does anyone know why Visual Studio is complaining? Is it my code or is this some strange anomaly in VS 2013?

Thank you for your time.

Answer 1

After more researching, I found that it was Design Mode trying to execute code it couldn't evaluate properly. To prevent Design Mode from doing this, wrap the offending code, like this:

if(!DesignerProperties.GetIsInDesignMode(this)) {
    ... Design Mode won't look at this ...
}

So, in my case, if I wrap the event registration, like this:

if(!DesignerProperties.GetIsInDesignMode(this)) {
    ExpandEvent = EventManager.RegisterRoutedEvent(
        "Expanded",
        RoutingStrategy.Bubble,
        typeof(RoutedEventHandler),
        typeof(Settings)
    );
}

... Design Mode will not break, and the application continues to run as expected.

Here are some cases where I found you may need to include such a preventative:

• Event Registration
• Accessing app.config
• Using C# to update any control properties at initialization time

Answer 2

That error means exactly what it says:

There is a RoutedEvent named Expanded that has already been registered with an OwnerType of Settings

That means that you have somehow duplicated this line of code:

ExpandEvent = EventManager.RegisterRoutedEvent(
    "Expanded",                    /* name */
    RoutingStrategy.Bubble,        /* routingStrategy */ 
    typeof(RoutedEventHandler),    /* handlerType */
    typeof(Settings)               /* ownerType <--- Duplicated */
);

You may have copied and pasted it into a different control, but forgot to update the OwnerType value from Settings to the correct class name. If you search for typeof(Settings) , you should find it.