Maximizing.ASP.dot.NET.Real.World.ObjectOriented.Development [Electronic resources] نسخه متنی

Getting Data In and Out

As fascinating as it might be to make a page display "Hello world," eventually your classes need to do something with data you provide and then return new data. You'll find that there are different ways to do the same thing.Chapter 2, "Classes: The Code Behind the Objects," you can get data in and out through a combination of parameters passed into methods, method return values, and properties. Listing 3.1 shows a class that uses only properties, with no parameters or return values for the methods. Listing 3.2 shows how you would call this class.

Listing 3.1. Methods that don't take parameters or have return values

C#

public class SomeClass
{
public void MyMethod()
{
_myName = "new name";
_myAge = 12;
}
private string _myName;
public string MyName
{
get { return _myName; }
set { _myName = value; }
}
private int _myAge;
public int MyAge
{
get { return _myAge; }
set { _myAge = value; }
}
}

VB.NET

Public Class SomeClass
Public Sub MyMethod()
_myName = "new name"
_myAge = 12
End Sub
Private _myName As String
Public Property MyName() As String
Get
Return _myName
End Get
Set
_myName = value
End Set
End Property
Private _myAge As Integer
Public Property MyAge() As Integer
Get
Return _myAge
End Get
Set
_myAge = value
End Set
End Property
End Class

Listing 3.2. Calling the class from Listing 3.1

C#

SomeClass ThisClass = new SomeClass();
ThisClass.MyName = "Jeff";
ThisClass.MyAge = 30;
ThisClass.MyMethod();
Trace.Warn(ThisClass.MyName); // outputs "new name"
Trace.Warn(ThisClass.MyAge.ToString()); // outputs "12"

VB.NET

Dim ThisClass As New SomeClass()
ThisClass.MyName = "Jeff"
ThisClass.MyAge = 30
ThisClass.MyMethod()
Trace.Warn(ThisClass.MyName) ' outputs "new name"
Trace.Warn(ThisClass.MyAge.ToString()) ' outputs "12"

We can rewrite this code to a similar class that doesn't use properties at all but arrives at a similar result, as shown in Listing 3.3 and Listing 3.4.

Listing 3.3. The refactored class without properties

C#

public class SomeClass
{
public string MyMethod(string oldName)
{
return "new name";
}
public int AnotherMethod(int oldAge)
{
return 12;
}
}

VB.NET

Public Class SomeClass
Public Function MyMethod(oldName As String) As String
Return "new name"
End Function
Public Function AnotherMethod(oldAge As Integer) As Integer
Return 12
End Function
End Class

Listing 3.4. Manipulating the class without properties

C#

SomeClass ThisClass = new SomeClass();
Trace.Warn(ThisClass.MyMethod("Jeff")); // outputs "new name"
Trace.Warn(ThisClass.AnotherMethod(30).ToString()); // outputs "12"

VB.NET

Dim ThisClass As New SomeClass()
Trace.Warn(ThisClass.MyMethod("Jeff")) ' outputs "new name"
Trace.Warn(ThisClass.AnotherMethod(30).ToString()) ' outputs "12"

I know what you're thinking"Wow, the second version sure looks easier. I'm going to do things that way!" Stop and think about it first because these classes don't do much of anything exciting. Imagine now that these classes have a dozen different methods that need to manipulate the same data. In the first example, you'd need to assign the data once to the properties and then execute your various methods. In the second example, you would need to pass in that data on every single method. Not a good use of your time! What's worse is that you can't get a number of different values out of the same method because the method can only return one value. That's why we have two separate methods to alter the name and age values in our example.

Another way to introduce data to the instantiated class right off the bat is to pass in values to the constructor of the class, as in Listing 3.5. Listing 3.6 shows how to pass in the data when you create a class instance. Your constructors can have parameters, just as a method can. You can also overload constructors, just as you would any other method.

Listing 3.5. Constructors with parameters

C#

public class SomeClass
{
public SomeClass(string someString)
{
// do something here with someString
}
}

VB.NET

Public Class SomeClass
Public Sub New(someString As String)
' do something here with someString
End Sub
End Class

Listing 3.6. Instantiating the class and passing in parameters

C#

SomeClass ThisClass = new SomeClass("my string");

VB.NET

Dim ThisClass As New SomeClass("my string")