I am trying to add rows to a public class that has public fields and am getting an error: Object reference not set to an instance of an object
Public Class EmailRecipient
EmailAddress As String = ""
FullName As String = ""
End Class
Public Class EmailDetails
Public FromEmail As String = ""
Public ToEmails As List(Of Emails) = nothing
End Class
Public Sub SetEmailDetails
'Populate EmailRecipient Class
Dim er As New EmailRecipient
er.EmailAddress = "rodney#norespect.com"
er.FullName = "Rodney Dangerfield"
'Populate EmailDetails Class
Dim ed As New EmailDetails
ed.FromEmail = "sender#danger.com" 'This works fine
ed.ToEmails.Add(er) 'Here error happens
End Sub
I'm guessing I need to create an instance of the EmailRecipient class before I can add an item to it.
Not sure how to do that with a Public Field in a Public Class??
It's been a rough day. I got up this morning, put a shirt on and a button fell off. I picked up my briefcase and the handle came off. I'm afraid to go to the bathroom.
Thanks for the help :-)
I'm guessing I need to create an instance of the EmailRecipient class
You already have an instance of the EmailRecipient class. That's your er variable. You actually have two errors here. First, you explicitly set ToEmails to Nothing:
Public ToEmails As List(Of Emails) = nothing
This means that your ToEmails variable is a Null Reference. It doesn't have an actual object yet.
The second issue is that you shouldn't get that excpetion, because this shouldn't even compile. You define ToEmails as a List(Of Emails), but tried to add an object of type "EmailRecepient" to it. That should be a compiler error. If it's not, you need to turn Option Strict or Option Infer back on.
So what you really need is an instance of a the List(Of EmailRecipient) type. Fix the bad line of code like this:
Public ToEmails As New List(Of EmailRecipient)
Related
I have a weird problem that I can't seem to figure out. Even weirder is that I'm fairly sure it has worked in the past, but not anymore.
I have a class where I define a variable as SortedSet. In a function, I can reference the variable, but its SortedSet attributes are not exposed. If I use them anyway, some of them work, others don't. If I create that variable inside my function, all works as expected.
This is the code:
Public Class MyTest
Public MySortedSet = New SortedSet(Of String)()
Public Sub New()
Dim MySortedSet2 = New SortedSet(Of String)()
'Constructor. To use this, add Dim MyTest As MyTest to the Form1_load sub.
Me.MySortedSet.add("Test")
For Each Item In Me.MySortedSet
MsgBox(Item) 'This does print Test
Next Item
Me.MySortedSet.add '.add not exposed
MySortedSet2.add '.add is exposed
End Sub
End Class
See the screenshot below. The first example only has 4 items, where the 2nd example has a full list of parameters. I need to fix this using the first example, so the ElementAt one works. It works in the second example, but not in the first. It gives the error that ElementAt is not part of this object.
How can I get the full list of parameters for me.MySortedSet.??????
You should declare MySortedSet as a Property:
Public Class MyTest
Public Property MySortedSet As New SortedSet(Of String)()
Public Sub New()
Dim MySortedSet2 As New SortedSet(Of String)()
Me.MySortedSet.Add("Test")
For Each item As String In Me.MySortedSet
Debug.WriteLine(item)
Next item
Me.MySortedSet.Add("Test")
MySortedSet2.Add("Test")
End Sub
End Class
You should also indicate variable types every time you declare a variable, even in a For Each statement.
Dim objects As New List(Of Object)
With New Object
.prop1 = "Property 1"
.prop2 = "Property 2"
objects.add(.instance) 'i mean instance of New Object
End With
is it possible.
I ask new question because last question has mislead information and I don't give right answer. so here code.
No it is not possible. The With statement basically creates an implicit variable. All you can do with that variable is access members and there is no member that returns a reference to the object itself.
If you want succinct code to create, populate and add an object to a list then do this:
myList.Add(New SomeType With {.SomeProperty = someValue,
.SomeOtherProperty = someOtherValue})
Interestingly, you can make it work the way you wanted if you create your own extension method. I was under the impression that you could not extend the Object class but either I was wrong or that has changed because I just tried in VB 2013 and it worked. You can write a method like this:
Imports System.Runtime.CompilerServices
Public Module ObjectExtensions
<Extension>
Public Function Self(Of T)(source As T) As T
Return source
End Function
End Module
and then do something like this:
With New SomeType
.SomeProperty = someValue
.SomeOtherProperty = someOtherValue
myList.Add(.Self())
End With
I'm not sure that that really provides any benefit though, given the availability of the object initialiser syntax that I demonstrated first.
Hmmm... I just realised that that's not actually extending the Object class. It was my original intention to try to do so but then I realised that a generic method was better because it would then return the same type as you call it on. I did just test it with a non-generic method extending type Object and it did still worked though.
You should to create your own class By example :
Public Class Car
Private _NumberCar As Integer
Public Property NumberCar() As Integer
Get
Return _NumberCar
End Get
Set(ByVal value As Integer)
_NumberCar = value
End Set
End Property
Private _ColorCar As Color
Public Property ColorCar() As Color
Get
Return _ColorCar
End Get
Set(ByVal value As Color)
_ColorCar = value
End Set
End Property
Private _OwnerName As String
Public Property OwnerName() As String
Get
Return _OwnerName
End Get
Set(ByVal value As String)
_OwnerName = value
End Set
End Property
End Class
and in the Class where you want to add the cars object do this :
Dim CarList As New List(Of Car)
Dim item As New Car
With item
.NumberCar = 1243
.ColorCar = Color.Red
.OwnerName = "Ibra"
End With
CarList.Add(item)
strong text
I'm trying to teach myself reflection and have been googling but I can't wrap my head around it entirely. I created a class called DataClass which contains a method called GetClassFromDB as you can see below, which will be inherited from multiple classes.
What I am attempting to do is have my dataclass read the TableName property that is defined within objResults. Once I pull in the tablename from objResults I would query the SQL database for a dataset. Once I have the dataset I would create a new object of the same TYPE inheriting this class (Which will be different types) and populate it from the dataset. Once I have the newly populated class I will return it for use.
I believe I have gotten most of the way there properly (Please correct me if there is a better way), but my real question is this. How can I create a new class of the type thats deriving that class from that string name that I getting in my code, or the type. I would want to have all the accessible properties from objResults available.
Namespace MyApp
Public Class DataClass
Private _TableName As String
Private _Name As String
Overridable ReadOnly Property TableName As String
Get
Return _TableName
End Get
End Property
Public Overloads Function GetClassFromDB() As Object
Try
Dim BaseObject As New Object
'Get the object name
Dim objName As String = MyBase.GetType().Name
'Gets the type thats calling this method
Dim objDerived As Type = MyBase.GetType()
'Get the property info to request the tablename from the derived class
Dim TableName As PropertyInfo = objDerived.GetProperty("TableName")
Dim TableNameString As String = TableName.GetValue(Me, Nothing).ToString
'Once I get the table name from objResults I can perform the SQL
Dim QueryResults as DataSet = SQLiteCLass.Query("Select * FROM TableNameString")
'Once I get data from the SQL I want to create a new object of the type deriving this method.
'In this example is objResults
Dim NewObject as objDerived
'Now I can fill my new object with the results and return it as an object
'THIS IS MY QUESTION - How can I create a new object of the TYPE that I receive from Reflection
Return False
Catch ex As Exception
Return False
End Try
End Function
End Class
End Namespace
and this is a sample class that would inherit my dataclass.
Public Class objResults
Inherits MyApp.DataClass
Private _GameID As Guid
Public Property GameID As Guid
Get
Return _GameID
End Get
Set(ByVal value As Guid)
_GameID = value
End Set
End Property
Public Overrides ReadOnly Property TableName As String
Get
Return "This is my tablename"
End Get
End Property
End Class
and this is how I would use this in code.
Dim objResult as New objResults
Dim TodaysResult as objResultsCollection
TodaysResult = objResult.GetClassFromDB()
Is it possible using Reflection or some other method to obtain a reference to a specific class instance from the name of that class instance?
For example the framework for the applications i develop heavily uses public class instances such as:
Public bMyreference as MyReference = new MyReference
Then throughout the application bMyReference is used by custom controls and code.
One of the properties of the custom controls is the "FieldName" which references a Property in these class instances (bMyReference.MyField) as a string.
What i would like to be able to do is analyze this string "bMyReference.MyField" and then refer back to the actual Instance/Property.
In VB6 I would use an EVAL or something simular to convert the string to an actual object but this obviously doesn't work in VB.net
What I'm picturing is something like this
Dim FieldName as String = MyControl.FieldName ' sets FielName to bMyReference.MyField
Dim FieldObject() as String = FieldName.Split(".") ' Split into the Object / Property
Dim myInstance as Object = ......... ' Obtain a reference to the Instance and set as myInstance
Dim myProperty = myInstance.GetType().GetProperty(FieldObject(1))
I don´t know if I´ve understood you well, but my answer is yes, you can do it by reflection. You´ll need to import System.Reflection namespace.
Here is an example:
' Note that I´m in namespace ConsoleApplication1
Dim NameOfMyClass As String = "ConsoleApplication1.MyClassA"
Dim NameOfMyPropertyInMyClass As String = "MyFieldInClassA"
' Note that you are getting a NEW instance of MyClassA
Dim MyInstance As Object = Activator.CreateInstance(Type.GetType(NameOfMyClass))
' A PropertyInfo object will give you access to the value of your desired field
Dim MyProperty As PropertyInfo = MyInstance.GetType().GetProperty(NameOfMyPropertyInMyClass)
Once you have MyProperty, uou can get the value of your property, just like this:
MyProperty.GetValue(MyInstance, Nothing)
Passing to the method the instace of what you want to know the value.
Tell me if this resolve your question, please :-)
EDIT
This would be ClassA.vb
Public Class MyClassA
Private _myFieldInClassA As String
Public Property MyFieldInClassA() As String
Get
Return _myFieldInClassA
End Get
Set(ByVal value As String)
_myFieldInClassA = value
End Set
End Property
End Class
I've found several aspx codes for forms which include the use of a "Set" function. When I try them out on the hosting server, I get an error message that "Set is no longer supported". Anyone know what replaced the "Set" command?
More specifically, how do I change this:
Dim mail
Set mail = Server.CreateObject("CDONTS.NewMail")
mail.To = EmailTo
mail.From = EmailFrom
mail.Subject = Subject
mail.Body = Body
mail.Send
to be VB.NET compatible?
If you mean the VB6 syntax
Set obj = new Object
then you can simply remove the Set
obj = new Object()
Set is a keyword in VB6, with the intrudction of VB.NET the keyword, as used in this context, was removed.
Formerly, Set was used to indicate that an object reference was being assigned (Let was the default). Because default properties no longer are supported unless they accept parameters, these statements have been removed.
Module Module1
Sub Main()
Dim person As New Person("Peter")
Dim people As New People()
people.Add(person)
'Use the default property, provided we have a parameter'
Dim p = people("Peter")
End Sub
End Module
Public Class People
Private _people As New Dictionary(Of String, Person)
Public Sub Add(ByVal person As Person)
_people.Add(person.Name, person)
End Sub
Default Public ReadOnly Property Person(ByVal name As String) As Person
Get
Return _people(name)
End Get
End Property
End Class
Public Class Person
Private _name As String
Public Sub New(ByVal name As String)
_name = name
End Sub
Public ReadOnly Property Name() As String
Get
Return _name
End Get
End Property
End Class
Some things to remember for .Net:
NEVER use Server.CreateObject() in .Net code. Ever.
NEVER Dim a variable without giving it an explicit type. Except for new Option Infer linq types
NEVER use the Set keyword. Except when defining a property.
In fact, in .Net you can get rid probably of the CDONTS dependancy entirely, as .Net has a built-in mail support:
Dim smtp As New System.Net.SmtpClient()
Dim message As New System.Net.MailMessage(EmailFrom, EmailTo, Subject, Body)
smtp.Send(message)