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Custom Control Overview

Posted By:Shashi Ray       Posted Date: March 25, 2009    Points: 25    Category: C#    URL: http://www.dotnetspark.com  

Custom Control Overview


Embedding user controls in a Windows form is just like adding a simple button or text box that are already provided with .NET. These basic controls were written essentially like you code your own controls. Typically the controls you design are to be used in multiple forms or to modularize your code. These reasons help reduce the amount of code you have to type as well as make it easier for you to change your implementation. There should almost never be any reason to duplicate code because it leaves a lot of room for bugs. So, implementing functionality specific to your control in the control's source code is a good idea. This reduces code duplication as well as modularize your code, which is a good programming guideline.

Custom controls are a key theme in .NET development. They can help your programming style by improving encapsulation, simplifying a programming model, and making user interface more "pluggable" (i.e., making it easier to swap out one control and replace it with a completely different one without rewriting your form code). Of course, custom controls can have other benefits, including the ability to transform a generic window into a state-of-the-art modern interface.


Generally, developers tackle custom control development for one of three reasons:


*   To create controls that abstract away unimportant details and are tailored
for a specific type of data. You saw this model in Chapter 6 with custom
ListView and TreeView examples.


*   To create controls that provide entirely new functionality, or just combine existing UI elements in a unique way.


*   To create controls with a distinct original look, or ones that mimic popular controls in professional applications (like Microsoft's Outlook bar) that aren't available to the masses.


In .NET, creating a custom control is as easy as creating an ordinary class. You simply inherit from the best possible ancestor and add the specific features you need. Best of all, you can create a custom control class as part of an existing project, and then decide later to place it in a separate assembly that can be shared with other programmers.


Types of Custom Controls


Developers often make a distinction between three or four types of controls:


*   User controls are the simplest type of control. They inherit from the System.Windows.Forms.UserControl class, and follow a model of composition.Usually, user controls combine more than one control in a logical unit (like a group of text boxes for entering address information).


*   Inherited controls are generally more powerful and flexible. With an inherited control, you choose the existing .NET control that is closest to what you want to provide. Then, you derive a custom class that overrides or adds properties and methods. The examples you've looked at so far in this book,including the custom TreeViews and ListViews, have all been inherited controls.


*   Owner-drawn controls generally use GDI+ drawing routines to generate their interfaces from scratch. Because of this, they tend to inherit from a base class like System.Windows.Forms.Control. Owner-drawn controls
require the most work and provide the most customizable user interface.


*   Extender providers, which aren't necessarily controls at all. These components add features to other controls on a form, and provide a remarkable way to implement
extensible user interface.


Shashi Ray

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