.NET EventHandlers - Generic or no?

Question

Every time I start in deep in a C# project, I end up with lots of events that really just need to pass a single item. I stick with the EventHandler/Event

Answer 1

I do believe that the recent versions of .NET have just such an event handler defined in them. That's a big thumbs up as far as I'm concerned.

/EDIT

Didn't get the distinction there originally. As long as you are passing back a class that inherits from EventArgs, which you are, I don't see a problem. I would be concerned if you weren't wrapping the resultfor maintainability reasons. I still say it looks good to me.

Answer 2

To make generic event declaration easier, I created a couple of code snippets for it. To use them:

• Copy the whole snippet.
• Paste it in a text file (e.g. in Notepad).
• Save the file with a .snippet extension.
• Put the .snippet file in your appropriate snippet directory, such as:

Visual Studio 2008\Code Snippets\Visual C#\My Code Snippets

Here's one that uses a custom EventArgs class with one property:

<?xml version="1.0" encoding="utf-8" ?>
<CodeSnippets  xmlns="http://schemas.microsoft.com/VisualStudio/2005/CodeSnippet">
  <CodeSnippet Format="1.0.0">
    <Header>
      <Title>Generic event with one type/argument.</Title>
      <Shortcut>ev1Generic</Shortcut>
      <Description>Code snippet for event handler and On method</Description>
      <Author>Ryan Lundy</Author>
      <SnippetTypes>
        <SnippetType>Expansion</SnippetType>
      </SnippetTypes>
    </Header>
    <Snippet>
      <Declarations>
        <Literal>
          <ID>type</ID>
          <ToolTip>Type of the property in the EventArgs subclass.</ToolTip>
          <Default>propertyType</Default>
        </Literal>
        <Literal>
          <ID>argName</ID>
          <ToolTip>Name of the argument in the EventArgs subclass constructor.</ToolTip>
          <Default>propertyName</Default>
        </Literal>
        <Literal>
          <ID>propertyName</ID>
          <ToolTip>Name of the property in the EventArgs subclass.</ToolTip>
          <Default>PropertyName</Default>
        </Literal>
        <Literal>
          <ID>eventName</ID>
          <ToolTip>Name of the event</ToolTip>
          <Default>NameOfEvent</Default>
        </Literal>
      </Declarations>
      <Code Language="CSharp"><![CDATA[public class $eventName$EventArgs : System.EventArgs
      {
        public $eventName$EventArgs($type$ $argName$)
        {
          this.$propertyName$ = $argName$;
        }

        public $type$ $propertyName$ { get; private set; }
      }

      public event EventHandler<$eventName$EventArgs> $eventName$;
            protected virtual void On$eventName$($eventName$EventArgs e)
            {
                var handler = $eventName$;
                if (handler != null)
                    handler(this, e);
            }]]>
      </Code>
      <Imports>
        <Import>
          <Namespace>System</Namespace>
        </Import>
      </Imports>
    </Snippet>
  </CodeSnippet>
</CodeSnippets>

And here's one that has two properties:

<?xml version="1.0" encoding="utf-8" ?>
<CodeSnippets  xmlns="http://schemas.microsoft.com/VisualStudio/2005/CodeSnippet">
  <CodeSnippet Format="1.0.0">
    <Header>
      <Title>Generic event with two types/arguments.</Title>
      <Shortcut>ev2Generic</Shortcut>
      <Description>Code snippet for event handler and On method</Description>
      <Author>Ryan Lundy</Author>
      <SnippetTypes>
        <SnippetType>Expansion</SnippetType>
      </SnippetTypes>
    </Header>
    <Snippet>
      <Declarations>
        <Literal>
          <ID>type1</ID>
          <ToolTip>Type of the first property in the EventArgs subclass.</ToolTip>
          <Default>propertyType1</Default>
        </Literal>
        <Literal>
          <ID>arg1Name</ID>
          <ToolTip>Name of the first argument in the EventArgs subclass constructor.</ToolTip>
          <Default>property1Name</Default>
        </Literal>
        <Literal>
          <ID>property1Name</ID>
          <ToolTip>Name of the first property in the EventArgs subclass.</ToolTip>
          <Default>Property1Name</Default>
        </Literal>
        <Literal>
          <ID>type2</ID>
          <ToolTip>Type of the second property in the EventArgs subclass.</ToolTip>
          <Default>propertyType1</Default>
        </Literal>
        <Literal>
          <ID>arg2Name</ID>
          <ToolTip>Name of the second argument in the EventArgs subclass constructor.</ToolTip>
          <Default>property1Name</Default>
        </Literal>
        <Literal>
          <ID>property2Name</ID>
          <ToolTip>Name of the second property in the EventArgs subclass.</ToolTip>
          <Default>Property2Name</Default>
        </Literal>
        <Literal>
          <ID>eventName</ID>
          <ToolTip>Name of the event</ToolTip>
          <Default>NameOfEvent</Default>
        </Literal>
      </Declarations>
      <Code Language="CSharp">
        <![CDATA[public class $eventName$EventArgs : System.EventArgs
      {
        public $eventName$EventArgs($type1$ $arg1Name$, $type2$ $arg2Name$)
        {
          this.$property1Name$ = $arg1Name$;
          this.$property2Name$ = $arg2Name$;
        }

        public $type1$ $property1Name$ { get; private set; }
        public $type2$ $property2Name$ { get; private set; }
      }

      public event EventHandler<$eventName$EventArgs> $eventName$;
            protected virtual void On$eventName$($eventName$EventArgs e)
            {
                var handler = $eventName$;
                if (handler != null)
                    handler(this, e);
            }]]>
      </Code>
      <Imports>
        <Import>
          <Namespace>System</Namespace>
        </Import>
      </Imports>
    </Snippet>
  </CodeSnippet>
</CodeSnippets>

You can follow the pattern to create them with as many properties as you like.

Answer 3

Since .NET 2.0

EventHandler<T>

has been implemented.