More on Commands, Input and the WPF - Code-Based Input Handling Versus Triggers
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The input handling techniques shown in this chapter all involve writing code that runs in response to some user input. If your reason for handling input is simply to provide some visible feedback to the user, be aware that writing an event handler or a custom command is likely to be overkill. It is often possible to create the visual feedback you require entirely within the user interface markup by using triggers. Triggers offer a declarative approach, where WPF does more of the work for you.
Any discussion of input handling in WPF would be incomplete without some mention of triggers. However, trigger-based input handling is radically different from the more traditional approach shown in this chapter, and it depends on aspects of WPF not yet described. Accordingly, it is dealt with later, in Chapters 8 and 9. So, for now just be aware of the two techniques and their intended usage: triggers are best suited for superficial responses, such as making a button change color when the mouse moves over it; event handling is appropriate for more substantive behavior, such as performing an action when the user clicks a button.
Where Are We?
Input is handled through events and commands, which use a routing system to allow simple uniform event handling regardless of how complex the structure of the user interface visuals might be. Input events are the lower level of these two mechanisms, reporting the exact nature of the user’s input in detail. Commands allow us to work at a higher level, focusing on the actions the user would like our applications to perform, rather than the specific input mechanism used to invoke the action.
* Ink is input written with a stylus, whether on a Tablet PC or a hand-held device, although the mouse can be used in a pinch.
* If you write custom elements, you should do the same. Chapter 18 describes how to do this.
* Capturing the mouse does not constrain its movement. It merely controls where mouse events are delivered.
* It is technically possible to provide a different class if you have special requirements. Command sources are happy to use any implementation of the ICommand interface, so you are not obliged to use the normal command routing mechanism. But most applications will use RoutedUICommand.
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 This article is excerpted from Programming WPF, Second Edition, written by Chris Sells and Ian Griffiths (O'Reilly, 2007; ISBN: 0596510373). Check it out today at your favorite bookstore. Buy this book now.
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