To understand the IEnumerable interface in VB.NET, I will create Student class and Course class. Since course has students I can use For...Each loop to get students from the course
First I will create the Student class. It has the FirstName and LastName property
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Public Class Student Private m_firstName As String Private m_lastName As String Public Property FirstName() As String Get Return m_firstName End Get Set(value As String) m_firstName = value End Set End Property Public Property LastName() As String Get Return m_lastName End Get Set(value As String) m_lastName = value End Set End Property End Class |
Then I will create the Course class which implements the IEnumerable interface
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Public Class Course Implements Collections.IEnumerable Private students() As Student Public Sub New(ByVal students() As Student) Me.students = students End Sub Function GetEnumerator() As IEnumerator Implements Collections.IEnumerable.GetEnumerator Return New StudentsEnum(students) End Function End Class |
Code explanation
- Line 9: You can see the
GetEnumerator()function which return theIEnumeratortype
Now I am going to create StudentEnum class which implements the IEnumerator
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Public Class StudentsEnum Implements IEnumerator Dim position As Integer = -1 Dim students() As Student Public Sub New(ByVal students() As Student) Me.students = students End Sub Public Sub Reset() Implements IEnumerator.Reset position = -1 End Sub Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext position = position + 1 If (position >= students.Length) Then Return False Else Return position < students.Length End If End Function Public ReadOnly Property Current() As Object Implements IEnumerator.Current Get Return (students(position)) End Get End Property End Class |
In this class you have to implement Reset(), MoveNext(), Current()
Code explanation
- Line 4: Position variable is used as the index of an array
- Line 5: students() array to hold students
- Line 10: Reset() function is used to reset the index position
- Line 15: MoveNext() function is used to increase the position
- Line 26: Current() function is used get the current object when you iterate
Now we can write the code to create some students objects and to the Course constructor method. Finally you can do the iterations
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Module Module1 Sub Main() 'Create two students Dim students(1) As Student Dim s1 As New Student() s1.FirstName = "John" s1.LastName = "Doe" students(0) = s1 Dim s2 As New Student() s2.FirstName = "Mark" s2.LastName = "Taylor" students(1) = s2 'Create VBCouse with Students Dim VBCourse As New Course(students) 'Now iterate to get students For Each stu As Student In VBCourse Console.WriteLine(stu.LastName) Next Console.ReadLine() End Sub End Module |