Lesson 1: Creating Composite Controls in .NET framework

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Lesson 1: Creating Composite Controls
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' VB Public Sub DisplayString(ByVal aString As String) Msgbox(aString) End Sub // C# public void DisplayString(string aString) { MessageBox.Show(aString); }
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For methods that return a value, create a Function (Visual Basic) or specify the return type (C#), as shown in this example:
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' VB Public Function DisplayString(ByVal aString As String, ByVal bString As String) As String Return aString & bString End Function // C# public string DisplayString(string aString, string bString) { return aString + bString; }
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Adding Properties to a Control Adding a property is similar to adding a method. You create a property definition and then implement the functionality required to return and set the value represented by the property. Usually, the underlying value for the property is stored in a private member variable. In Visual Basic, you use the Property keyword to create a property. In C#, you simply implement the getter and setter for the property. The following example demonstrates how to implement a property, including a member variable to contain the value.
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' VB Private mUnitsOnHand Public Property UnitsOnHand() As Integer Get Return mUnitsOnHand
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End Get
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Set(ByVal value As Integer)
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mUnitsOnHand = value End Set End Property // C# private int mUnitsOnHand; public int UnitsOnHand {
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get { return mUnitsOnHand; }
set { mUnitsOnHand = value; }
You can create a read-only property by using the ReadOnly keyword in Visual Basic or by simply omitting the setter in C#. An example is shown here:
' VB Private mUnitsOnHand
Public ReadOnly Property UnitsOnHand() As Integer
Return mUnitsOnHand
End Get
End Property
// C# private int mUnitsOnHand;
public int UnitsOnHand
get { return mUnitsOnHand; }
If creating a read-only property, you must set the member variable that represents the property s value in code.
Adding Events to a Control
You can add events to a control that can be raised to notify the rest of the application that something interesting has happened. Once an event has been added to a class or control, it can be raised in code to send a notifica tion to the rest of the application.
In Visual Basic, you can create an event by using the Event keyword and specifying the name and signature of the event, as shown here:
' VB Public Event Bang(ByVal decibels As Integer)
On the other hand, C# requires an explicit delegate to be present to specify the signa ture before the event keyword can be used to create a new event. The following exam ple demonstrates how to create an event in C#:
// C# public delegate void Sound(int decibels);
public event Sound Bang;
Note that you specify the delegate itself, not an instance of the delegate.
Lesson 1: Creating Composite Controls
You can raise an event in code by using the RaiseEvent keyword in Visual Basic or by simply calling the Event like you would a method in C#. An example is shown here:
' VB RaiseEvent Bang(100) // C# this.Bang(100);
Exposing the Properties of Constituent Controls
When constituent controls are added to a composite control, they are given an access level of Friend in by-default Visual Basic and private in C#. In both cases, the constit uent controls will be inaccessible to classes in other assemblies. If you want to allow other assemblies to configure parts of the constituent controls, you must expose the properties of the constituent controls by wrapping them in a property declaration and then writing code in the composite control s property to get and set the value of the constituent control s property. For example, suppose you wanted to expose the BackColor property of a constituent Button. You might create a property in the composite control called ButtonBackColor, in which you return the BackColor property of the con stituent Button in the getter and set the constituent BackColor property of the Button in the setter. An example of how you might implement this is shown here:
' VB Public Property ButtonBackColor() As System.Drawing.Color Get Return Button1.BackColor End Get Set(ByVal value As System.Drawing.Color) Button1.BackColor = value End Set End Property // C# public System.Drawing.Color ButtonBackColor { get { return Button1.BackColor; } set { Button1.BackColor = value; } }
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