Is it possible to set code behind a resource dictionary in WPF for event handling?

I think what you’re asking is you want a code-behind file for a ResourceDictionary. You can totally do this! In fact, you do it the same way as for a Window:

Say you have a ResourceDictionary called MyResourceDictionary. In your MyResourceDictionary.xaml file, put the x:Class attribute in the root element, like so:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    x:Class="MyCompany.MyProject.MyResourceDictionary"
                    x:ClassModifier="public">

Then, create a code behind file called MyResourceDictionary.xaml.cs with the following declaration:

namespace MyCompany.MyProject
{
    partial class MyResourceDictionary : ResourceDictionary
    { 
       public MyResourceDictionary()
       {
          InitializeComponent();
       }     
       ... // event handlers ahead..
    }
}

And you’re done. You can put whatever you wish in the code behind: methods, properties and event handlers.

== Update for Windows 10 apps ==

And just in case you are playing with UWP there is one more thing to be aware of:

<Application x:Class="SampleProject.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:rd="using:MyCompany.MyProject">
<!-- no need in x:ClassModifier="public" in the header above -->

    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>

                <!-- This will NOT work -->
                <!-- <ResourceDictionary Source="/MyResourceDictionary.xaml" />-->

                <!-- Create instance of your custom dictionary instead of the above source reference -->
                <rd:MyResourceDictionary />

            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>

</Application>