08 gui 11

GUI Applications Development Using .NET Framework
Objectives

In this session, you will learn to:
Work with user-defined components in the .NET applications

Ver. 1.0 Session 11 Slide 1 of 20

Creating a .NET Component

To create a component in .NET, the user needs to identify
the type of component and its properties and methods.
While creating a component, a user needs to:
Use constructors
Add properties
Add methods


Creating a .NET Component (Contd.)

Using Constructors:
.NET allows the passing of arguments to the object constructor
by adding a constructor to the component's class module.
A component can have the following types of constructors:
Public constructors
Internal constructors
Private constructors



Adding Properties:
– Declaring a property allows you to control how a value is
changed or read.
– You can declare a private variable that cannot be accessed
from outside a class.
– You can create a property where you can have the Get and
Set accessors to read and set the value of a private variable.



Adding Methods:
A method in a class can be:
a procedure that performs an operation on the data within the
class.
a function that performs some operation on the data and returns
the data from the class.
The method must be declared public to call a method from an
instance of this class.
If a method is declared private, only methods within the same
class can call that method.


Just a minute

Name the two main categories of .NET components.

Answer:
1. In-process components
2. Out-of-process components


Creating User-Defined Controls in .NET Applications

There may be situations when you require a control, which
performs actions that are not provided by any built-in control
or need some enhanced feature.
The .NET Framework provides three types of user-defined
controls. These are:
User control
Controls inherited from an existing control
Custom control


Creating User-Defined Controls in .NET Applications (Contd.)

User Controls:
– You combine two or more controls to create a new control.
– User controls are also called as composite controls.
– All user controls inherit the
System.Windows.Forms.UserControl class.
– The UserControl class can be used to combine the
functionality of various controls into one unit, which can be
reused.
– The UserControl class presents a single and unified
interface.
– This interface contains members inherited from the control
classes.



Controls Inherited from an Existing Control:
You can inherit from an existing control and then add
additional features to it.
When you inherit a control from an existing control, the new
control will have all the features of the inherited control.


Just a minute

Name the method that has to be overridden to change the
appearance of the control that is inherited from an existing
control.

Answer:
– The OnPaint() method



Custom Controls:
– Custom controls have the highest degree of customizability.
– Users can build a control that has very little resemblance with
the built-in controls in terms of both appearance and
functionality.
– All custom controls inherit from the
System.Windows.Forms.Control class.


Just a minute

Name the class to be inherited for creating a custom
control.

Answer:
System.Windows.Forms.Control


Demo: Implementing a .NET Component

Problem Statement:
Build a nonvisual .NET component called TimeComponent. It
should get the current date and time from the host computer. In
addition, create an application that will use this component and
display the time returned.


Demo: Implementing a .NET Component (Contd.)

Solution:
To use a component, you need to perform the following tasks:
1. Create a .NET component.
2. Create a user application.


Demo: Creating a User Control

Problem Statement:
Build a user control called DigitalClock. This should contain a
label control that displays time. In addition, create an
application that will use this control.


Demo: Creating a User Control (Contd.)

Solution:
To build a user control and an application, you need to perform
the following tasks:
1. Create a user control.


Demo: Creating Inherited Controls

Problem Statement:
Build a NumericTextBox control that contains a TextBox
control. The latter should accept only a numeric value as input.
In addition, create an application that will use this control.


Demo: Creating Inherited Controls (Contd.)

Solution:
To create the NumericTextBox control and an application,
which will implement the NumericTextBox control, you need to
perform the following tasks:
1. Create an inherited control.


Summary

In this session, you learned that:
To create a component in .NET, the user needs to identify the
type of component and its properties and methods.
While creating a component, a user needs to:
• Use constructors
• Add properties
• Add methods
In .NET programming environment, you can have the following
types of constructors:
Public constructor
Internal constructor
Private constructor


Summary (Contd.)

The .NET Framework provides three types of user-defined
controls. These are:
User controls
Controls inherited from an existing control
Custom controls


08 gui 11

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