Windows Phone 8: Moving Event Handlers into the base View class - wpf

Question

I have a number of views in my Windows Phone 8 app that share a lot of similarity, so I created a base class to contain the common logic. In general, this approach has worked great, but with one limitation - I am unable to move the common event handling logic into the base class. Here is the simplified version of what I am trying to achieve:
The base class defines a method which my sub-classes should use to handle a button click event in their respective application bars.
public class BaseView : PhoneApplicationPage
{
protected void OnButtonClick(object sender, EventArgs e)
{
MessageBox.Show("Button Pressed");
}
}
The XAML for the inheriting view looks like this (showing only the relevant part). Note the ApplicationBarIconButton's event handler. My intention is that the OnButtonClick method, defined in the base view, is called.
<base:BaseView
x:Class="EventHandlersInBaseClassBugRepro.MainPage"
xmlns:base ="clr-namespace:EventHandlersInBaseClassBugRepro"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
..... >
<phone:PhoneApplicationPage.ApplicationBar>
<shell:ApplicationBar IsMenuEnabled="False">
<shell:ApplicationBarIconButton
IconUri="/Assets/Tiles/FlipCycleTileSmall.png"
Text="Click"
Click="OnButtonClick"/>
</shell:ApplicationBar>
</phone:PhoneApplicationPage.ApplicationBar>
The application compiles, but at runtime I am getting this exception:
{System.Windows.Markup.XamlParseException: Failed to assign to property 'Microsoft.Phone.Shell.ApplicationBarIconButton.Click'. [Line: 22 Position: 23]
at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
at EventHandlersInBaseClassBugRepro.MainPage.InitializeComponent()
at EventHandlersInBaseClassBugRepro.MainPage..ctor()}
I saw a similar question here Silverlight: Can I set an event to a base class event handler in XAML?. My interpretation of the answer suggests that the approach I am using should work, yet the exception.
Is what I am trying to do possible?

Answer 1

Remember Events are a delegate that should only be invoked in the class that declared them.
In your scenario you havent declared an Event in the BaseView.
Also mark the OnButtonClick invoke method as Virtual so that it can be overridden in derived classes. Try
public class BaseView : PhoneApplicationPage
{
public event EventHandler ButtonClicked;
public virtual void OnButtonClick(object sender, EventArgs e)
{
MessageBox.Show("Base Button Click");
}
}
In your derived class .cs you will need to override OnButtonClick like this
public override void OnButtonClicked(object sender, EventArgs e)
{
// do derived class logic here
MessageBox.Show("Derived class hit");
// calls BaseView event invoke method
base.OnButtonClicked(sender, e);
}
Hope that helps