Class concept (a class accessing property then accessing method)

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Hello Everyone

I have a class called Car:

VB

Public Class Car
    'Property
    Public theColor() As Color

    'Method
    Public speed As Double
    Public Function run()
        Return speed
    End Function
End Class

In another class I create an instance of Car Class:

VB

Public Class SUV
    Dim newCar As New Car

    Private Sub setColor()
        'set theColor property
        newCar.theColor = Color.Red
    End Sub

    Private Sub testDrive()
        'call run() function
        newCar.run()
    End Sub
End Class

From the code above,
If I want to set a property of a class I just write an instance and the property:
newCar.theColor = Color.Red
Also if I want to call a method of a class I just write an instance then call the function or sub:
newCar.run()

But I dont understand how can a line of code be like this, for example:

VB.NET

Dim dgv As New DataGridView
dgv.Rows.Add()

The code above show that an instance (dgv) call property (Rows) than call a method (Add())

Back to my class (the Car And SUV)
How to write the code in my class if i want to call the method like this?

VB

newCar.theColor.resetColor()

And another code:

VB

newCar.theColor.setColor() = Color.Red

I am sorry if the question's title isnt match with what i've asked.

Thanks

What I have tried:

I have no idea how to to try to solve my question above

Posted 10-Sep-16 18:42pm

Mang Irpan

Updated 12-Sep-16 23:44pm

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2 solutions

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OriginalGriff · Accepted Answer · 2016-09-10T19:58:00

When you write this:

VB

Dim dgv As New DataGridView
dgv.Rows.Add(obj)

You create an instance of the DataGridView, and then use it:
dgv.Rows is a Property of DataGridView which returns a n instance of the DataGridViewRowCollection class which is the rows in the DGV: MSDN[^]
The DataGridViewRowCollection has a Method Add which adds a row to the collection, and hence to the DGV.
To do something similar, you'd need an extra class:

VB

Public Class MyColor
	Public Sub ResetColor()
	End Sub
End Class
Public Class Car
	Public Property TheColor() As MyColor
		Get
			Return m_TheColor
		End Get
		Set
			m_TheColor = Value
		End Set
	End Property
	Private m_TheColor As MyColor
End Class
...
Public Sub myMethod()
	Dim newCar As New Car()
	newCar.TheColor.ResetColor()
End Sub

Quote:
an we do the similiar way to create property or method in another language? like java or c#. And is this a part of OOP concept? what did i miss in my learning of programming?

Yes. For example, the above in C# is:

C#

public class MyColor
    {
    public void ResetColor()
        {
        }
    }
public class Car
    {
    public MyColor TheColor { get; set; }
    }
...
    public void myMethod()
        {
        Car newCar = new Car();
        newCar.TheColor.ResetColor();
        }

And it's similar code for Java.
Properties aren't strictly part of OOPs - they are just "syntactic sugar" for the method calls involved that let you treat the property as a variable - but most OOPs languages implement them.

What did you miss? :laugh: I don't know, I wasn't there!

Maciej Los · Accepted Answer · 2016-09-12T23:44:00

I'd strongly recommend to read about Inheritance[^] and Polimorphism[^].

A Car class have to be a base class. A Suv class should inherits from Car (as it is a type of Car). Am i right?

For example:

VB.NET

Public Class Car
	
	Private dc As Integer = 5
	Private c As Drawing.Color = Drawing.Color.Gray
	
	Public Sub New ()
		'default constructor
		
	End Sub
	
	Public Sub New (ByVal doorsCount As Integer, ByVal color As Drawing.Color)
		dc = doorsCount
		c=  color
	End Sub
	
	Public Property DoorsCount As Integer
		Get
			Return dc
		End Get
		Set (ByVal value As Integer)
			dc = value
		End Set
	End Property
	
	Public Property Color As Drawing.Color
		Get
			Return c
		End Get
		Set (ByVal value As Drawing.Color)
			c = value
		End Set
	End Property

End Class

Public Class Suv
	Inherits Car
	
	Public Sub New ()
		'default constructor
		MyBase.DoorsCount = 4
                MyBase.Color = Drawing.Color.Green		
	End Sub
	
	Public Sub New (ByVal doorsCount As Integer, ByVal color As Drawing.Color)
		MyBase.DoorsCount = doorsCount
		MyBase.Color =  color
	End Sub
	
	
End Class

[EDIT#1]

Usage:

VB.NET

Dim carcar As Car = New Car()
Console.WriteLine(New String("-", 25))
Console.WriteLine("Car details:")
Console.WriteLine("  - doors: {0}", carcar.DoorsCount)
Console.WriteLine("  - color: {0}", carcar.Color.ToString())


Dim suvcar As Suv = New Suv()
Console.WriteLine(New String("-", 25))
Console.WriteLine("Suv details:")
Console.WriteLine("  - doors: {0}", suvcar.DoorsCount)
Console.WriteLine("  - color: {0}", suvcar.Color.ToString())

suvcar.DoorsCount = 3
suvcar.Color = Drawing.Color.Yellow

Console.WriteLine(New String("-", 25))
Console.WriteLine("Suv details:")
Console.WriteLine("  - doors: {0}", suvcar.DoorsCount)
Console.WriteLine("  - color: {0}", suvcar.Color.ToString())

Result:

-------------------------
Car details:
  - doors: 5
  - color: Color [Gray]
-------------------------
Suv details:
  - doors: 4
  - color: Color [Green]
-------------------------
Suv details:
  - doors: 3
  - color: Color [Yellow]

[EDIT #2]
As you can see, you don't need getter/setter inside custom method. You can achieve that using only properties.

Try! Good luck!

Class concept (a class accessing property then accessing method)

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