Event Handlers in WPF - Page 1
       by kirupa  |  1 March 2007

Whenever you click on a button or type some text into a form in your browser, you are using events. More than likely, you never think about this, because it just works. You don't worry about how the mouse click is recognized, how your application knows which key was pressed, etc. The reason is that many of these lower level details are handled by your graphics framework itself. Even as a developer, your work with events is largely on the surface of what really goes on behind the scenes, but there is plenty of surface area to cover though! So, in this tutorial, I will explain how to use event handlers in the Windows Presentation Foundation (WPF).

Event Handlers
Don't let the introduction scare you though. Event handling is extremely common, and if you've ever made your application do something when a button was clicked, you already know most of what is to know about using event handlers.

An event handler is simply a method (function) that receives the input from a device such as a mouse or keyboard and does something with it. Like its name implies, it handles events - more specifically, input events. For example, the following code shows an event handler called ButtonOkClicked that is fired when a button is clicked:

private void ButtonOkClicked(object sender, RoutedEventArgs e)

{

this.Close();

}

There are really two things that need to be done when using events:

1. You need to bind an event handler to a Control (button, text field, menu, etc.).
2. You need to specify an event handler that receives and reacts to an event.

In this article, I will go over event handlers and how to use them with events. I will provide code examples to reinforce what I will be explaining, but this is more of an article explaining event handlers as opposed to a tutorial where you create a small application using event handlers.

Binding a Event to a Event Handler
Let's first look at how to bind an event to an event handler. There are two ways of doing this. You can (1) either use an IDE such as Expression Blend or Visual Studio's WPF Designer (see blog post), or (2) you can bind a control to an event using code itself. The end result is the same, so let's look at both the visual as well as code-based approaches.

Visual Approach
The visual approach is what most of you will use because there are great tools for designing GUIs using WPF. I won't go into the details of either Visual Studio or Blend in this tutorial, but if you have, for example, a button, you can view a list of the events and assign an event handler next to the event you wish to fire:

[ assigning a click event to an event handler called ButtonOkClicked ]

In the visual view, you simply find the event that you wish to bind your control to such as Click, and specify the name your event handler will take. When you press Enter you will be taken to the code view where you can see the event handler displayed with the name you provided.

Trivia - Look at the XAML!

If you look at the XAML for the above event-binding, you will see both the Click event as well as our event handler ButtonOkClicked appear:

<Button HorizontalAlignment="Left" Margin="130,92,0,86" x:Name="btnOK" Width="80" Content="OK" Click="ButtonOkClicked"/>

It is the above XAML definition that tells your final application to route all Click events attached to the button to the ButtonOkClicked event handler. A program like Blend or Visual Studio's Designer serves primarily to provide a nice interface for creating the XAML snippet I posted above.

On the next page, let's take a look at the code based approach.

Onwards to the next page!

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