I am working on an application to add users to groups in Active Directory, with two classes: ADUser and Student, which inherits from ADUser.
public class ADUser
property UserID as string
property MemberOf as new List(Of String)
(etc)
end class
public class Student inherits ADUser
property subjects as new list(Of Subject) 'Subject is a class of multiple strings
end class
I am attempting to copy the subject name from the subjects list to the MemberOf list, which results in a NullReferenceException (Object reference not set to an instance of an object). The following code generates an error on the me.MemberOf.Add line:
Function ConvertSubjectsToGroupMembership() As Boolean
Try
For Each s As Subject In Subjects
Me.MemberOf.Add(String.Format("t.{0}", s.ShortName).ToString)
Next
Return True
Catch ex As Exception
Return False
End Try
End Function
My understanding of inheritance is that the MemberOf list should be created when the Student object is created, however this does not seem to be the case.
Any assistance is appreciated.
Edit:
I managed to work around the issue by modifying the function to create a list(of String), which is then copied to the MemberOf property:
Function ConvertSubjectsToGroupMembership() As Boolean
Dim SubjectShortNameList As New List(Of String)
For Each s As Subject In Subjects
SubjectShortNameList.Add(String.Format("t.{0}", s.ShortName).ToString)
Next
Try
MemberOf = SubjectShortNameList
Return True
Catch ex As Exception
Return False
End Try
End Function
It works, but I'm sure there's a better way to do it. I look forward to reading the answers/opinions of others!
It looks like you are nulling out MemberOf somewhere else in code. Assuming ConvertSubjectsToGroupMembership is a function on Student I ran the code and it worked fine. You could try expanding the property so you can set a breakpoint. This will allow you to find out where the Null is being introduced.
Public Class ADUser
Property UserID As String
Private _MemberOf As New List(Of String)
Public Property MemberOF As List(Of String)
Get
Return _MemberOf
End Get
Set(ByVal value As List(Of String))
_MemberOf = value ***'breakpoint here***
End Set
End Property
End Class
Related
After creating a List(Of T), I want to create aBoolean function. First, we will ask data to add an object in the list. However, in case this new object has the same "DNI" (String attribute from the class Aspirante), then we cannot include this new Object in the list. Therefore, it should be True when we have an Object with the same attribute and False when we don´t, so we can add the new object.
Below is the code I did:
Public Class Oposicion
Private datos As New List(Of Aspirante)()
Public Function Alta(ByRef objAspirante As Aspirante) As Boolean
If datos.Contains(objAspirante.DNI) Then
Return True
Else
datos.Add(objAspirante)
Return False
End If
End Function
End Class
However it doesn´t work. I have no clue on how to do it. Sorry if I was not clear enough.
This doesn't answer your question directly but it involves a significant amount of code, so it won't work in a comment.
You probably shouldn't be using a List(Of T) in the first place. The HashSet(Of T) already includes functionality to prevent adding duplicate items, so that may be a better option. If you want to compare objects on a specific property value then you need to first create a comparer based on that:
Public Class Thing
Public Property Stuff As String
End Class
Public Class ThingComparer
Implements IEqualityComparer(Of Thing)
Public Overloads Function Equals(x As Thing, y As Thing) As Boolean Implements IEqualityComparer(Of Thing).Equals
Return x.Stuff.Equals(y.Stuff)
End Function
Public Overloads Function GetHashCode(obj As Thing) As Integer Implements IEqualityComparer(Of Thing).GetHashCode
Return obj.GetHashCode()
End Function
End Class
You then create a HashSet(Of T) that uses that comparer to determine equality:
Dim things As New HashSet(Of Thing)(New ThingComparer)
You can then just add items as you please by calling Add. That will either add the new item and return True or it will not not add the duplicate item and return False:
Dim variousStuff = {"One", "Two", "One"}
For Each stuff In variousStuff
Dim something As New Thing With {.Stuff = stuff}
If things.Add(something) Then
Console.WriteLine($"'{stuff}' was added successfully.")
Else
Console.WriteLine($"'{stuff}' is a duplicate and was not added.")
End If
Next
The potential drawback is that HasSet(Of T) does not implement IList(Of T), so you cannot access items by index. It does implement ICollection(OF T) though, so it does have a Count property and you can enumerate it with a For Each loop.
You can create a List(Of String) containing the just the DNI property of each object in datos. Then see if the DNI of objAspirante is contained in lst.
Public Class Oposicion
Private datos As New List(Of Aspirante)()
Public Function Alta(objAspirante As Aspirante) As Boolean
Dim lst As New List(Of String)
For Each a As Aspirante In datos
lst.Add(a.DNI)
Next
If lst.Contains(objAspirante.DNI) Then
Return True
Else
datos.Add(objAspirante)
Return False
End If
End Function
End Class
If you can change the type of datos, this might be easier.
Public Class Oposicion
Private datos As New Dictionary(Of String, Aspirante)()
Public Function Alta(objAspirante As Aspirante) As Boolean
If datos.ContainsKey(objAspirante.DNI) Then
Return True
Else
datos.Add(objAspirante.DNI, objAspirante)
Return False
End If
End Function
End Class
If you want to stick with your existing List(Of Aspirante), then simply use .Any() and pass it a Lambda to determine if one already exists. It'd look something like this:
Public Function Alta(ByVal objAspirante As Aspirante) As Boolean
If Not datos.Any(Function(x) x.DNI = objAspirante.DNI) Then
datos.Add(objAspirante)
Return True ' your description and code did not match for these!
End If
Return False ' your description and code did not match for these!
End Function
Note my comment on the Return lines...your code and description did not match here.
Public Class Products
Private zCriteria As String
Public Property Criteria As String
Get
Return zCriteria
End Get
Set(value As String)
zCriteria = value
End Set
End Property
Private zProductList As New List(Of Product)
Public Property ProductList As List(Of Product)
Get
Return zProductList
End Get
Set(value As List(Of Product))
zProductList = value
End Set
End Property
End Class
Public Class Product
Private zCriteriaList As List(Of Criterias)
Public Property CriteriaList As List(Of Criterias)
Get
Return zCriteriaList
End Get
Set(value As List(Of Criterias))
zCriteriaList = value
End Set
End Property
End Class
Public Class Criterias
Private zCrPropName As String
Public Property CrPropName As String
Get
Return zCrPropName
End Get
Set(value As String)
zCrPropName = value
End Set
End Property
Private zCritCode As String
Public Property CritCode As String
Get
Return zCritCode
End Get
Set(value As String)
zCritCode = value
End Set
End Property
Private zcrPropValue As String
Public Property crPropValue As String
Get
Return zcrPropValue
End Get
Set(value As String)
zcrPropValue = value
End Set
End Property
End Class
For Each oProducts As Products In oAssigment.ProductsList
For Each oproduct As Product In oProducts.ProductList
For Each cr As Criterias In oproduct.CriteriaList
cr.CrPropName = "Product Name" 'some object property name
cr.CritCode = "PN"
cr.crPropValue = "" ' Value of property "Product Name"
Next
Next
Next
It is all made to have different properties of some object depending on options set in text file. It is only a sample o usage.
conditions:
Criterias on applications start is same for all objects (=Product) i want to read.
Every time on start, application read options file where is defined few property names and codes (values i want get from objects). So every run can be initiated different quantity of properties to read. It means i can not have hard-coded names of properties.
Someone can advice me how to predefine "CrPropName" and "CritCode" on app start so many times how much property names defined in options and after that populate it so many times as how many objects exist from which i read these property values.
p.s. I am not very professional at coding and sorry for my language
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
table 1. MerchantBusiness
table 2. MerchantServices
i want to display both tables data in a single view.
I want to display the MerchantBusiness details on the view. very basic business name, address etcc.
the MerchantServices is a list of services that the business has.
so i first created the viewModel
Public Class MerchantServicesModel
Public Property MerchantViewModel() As Merchant
Get
Return _Merchant
End Get
Set(value As Merchant)
_Merchant = value
End Set
End Property
Private _Merchant As Merchant
Public Property ServiceViewModel() As IEnumerable(Of MerchantService)
Get
Return _Services
End Get
Set(value As IEnumerable(Of MerchantService))
_Services = value
End Set
End Property
Private _Services As MerchantService
End Class
and in my controller im binding the two tables to the viewModel
Function Index(id As Integer) As ActionResult
Dim db As New MerchantEntities
Dim MerchantDetails As New MerchantServicesModel
MerchantDetails.MerchantViewModel = db.Merchants.Find(id)
MerchantDetails.ServiceViewModel = (From m In db.MerchantServices
Where m.MerchantID = id
Select m).ToList()
Return View(MerchantDetails)
End Function
My View
#ModelType MerchantServicesModel
#Code
Layout = "~/Views/Shared/_Layout.vbhtml"
End Code
#Html.DisplayFor(Function(model) model.MerchantViewModel.BusinessName)
#For Each item In Model.ServiceViewModel
#Html.DisplayFor(Function(model) item.ServiceName)
Next
i was thinking that the MerchantBusiness is not a full list just details of the particular business
but the MerchantServices is a IEnumerable list so i create a table and style blah blah..
now the error im getting is
Additional information: Unable to cast object of type 'System.Collections.Generic.List`1[VBClassMVC.MerchantService]' to type 'VBClassMVC.MerchantService'.
am i missing something, or am i binding incorrectly?
thank you.
Hay all i manged to fix that. Here is the updated ViewModel
Public Property ServiceViewModel() As IEnumerable(Of MerchantService)
Get
Return _Services
End Get
Set(value As IEnumerable(Of MerchantService))
_Services = value
End Set
End Property
Private _Services As IEnumerable(Of MerchantService)
i needed to add IEnumerable(Of MerchantService) to the _Services Private variable..
I get a null reference exception when I try to use this webservice I'm working on. I have two fields in the object ipadarticle called fullname and tags, which are declared to be lists, so that ipadarticle can return multiple tags and authors. The null reference exception points to
ipadarticle2.FullName.Add(a_var.firstname + " " + a_var.lastname)
ipadarticle2.Tag.Add(a_var.tagtext)
I'm pretty new to vb programming, so I'm not really to sure what is causing this. To clarify, what is going on is that this stored procedure is fetching entries from a db, which has a list of articles with -among other things- tags and authors associated with it. Since articles have multiple tags and authors there are multiple entries for each article. When I return the info in the web service I am trying to make it so that only one ipadarticle object is returned for reach article, and then that contains a list of the multiple tags and authors associated with each article. I'm having a headache trying to figure this out.
Dim lq As New lqDFDataContext
Dim var = lq.mobile_IpadGetSavedArticlesAR(simpuser.UserID, tempParamKW(0), tempParamKW(1), tempParamKW(2), tempParamKW(3), tempParamKW(4), pageNum, pageLen)
Dim ipadarticle2 As New ipadArticle()
For Each a_var In var
If a_var.articleID <> temp Then
If flag = 0 Then
result.add(ipadarticle2)
Dim ipadarticle1 As New ipadArticle()
ipadarticle2 = ipadarticle1
End If
ipadarticle2.ArticleID = a_var.articleID
ipadarticle2.PublishedOn = a_var.publicationdate
ipadarticle2.Title = a_var.title
ipadarticle2.MedAbbr = a_var.medabbr.Replace(" ", "-").ToLower()
ipadarticle2.FullName.Add(a_var.firstname + " " + a_var.lastname)
ipadarticle2.Tag.Add(a_var.tagtext)
flag = 1
Else
ipadarticle2.Tag.Add(a_var.tagtext)
ipadarticle2.FullName.Add(a_var.firstname + " " + a_var.lastname)
flag = 0
End If
temp = a_var.articleID
Next
End If
Return result
ipadArticle class:
Imports Microsoft.VisualBasic
Public Class ipadArticle
Inherits SimpleObject
Public Sub New()
End Sub
Private _ArticleID As Integer
Public Property ArticleID() As Integer
Get
Return _ArticleID
End Get
Set(ByVal value As Integer)
_ArticleID = value
End Set
End Property
Private _Title As String
Public Property Title() As String
Get
Return _Title
End Get
Set(ByVal value As String)
_Title = value
End Set
End Property
Private _PublishedOn As String
Public Property PublishedOn() As String
Get
Return _PublishedOn
End Get
Set(ByVal value As String)
_PublishedOn = value
End Set
End Property
Private _MedAbbr As String
Public Property MedAbbr() As String
Get
Return _MedAbbr
End Get
Set(ByVal value As String)
_MedAbbr = value
End Set
End Property
Private _Tag As List(Of String)
Public Property Tag() As List(Of String)
Get
Return _Tag
End Get
Set(ByVal value As List(Of String))
_Tag = value
End Set
End Property
Private _FullName As List(Of String)
Public Property FullName() As List(Of String)
Get
Return _FullName
End Get
Set(ByVal value As List(Of String))
_FullName = value
End Set
End Property
End Class
The most likely cause is that the objects FullName and Tag have not been created (are Nothing) in ipadarticle2. These should most likely be created as new objects in the class constructor.
EDIT:
Based on the posted class, the above assumption was correct: FullName and Tag are defined as List(Of String), but the backing members are never created.
This can be fixed in a couple of ways:
1) Instantiate the backing member variables directly in their definition, i.e.:
Private _FullName As New List(Of String)
2) Instantiate the backing member variables in the constructor:
Public Sub New()
_FullName = New List(Of String)
_Tag = New List(Of String)
End Sub
3) Instantiate the backing member variable in the getter if it is nothing:
Public Property Tag() As List(Of String)
Get
If _Tag Is Nothing Then
_Tag = New List(Of String)
End If
Return _Tag
End Get
Basically, any variable types other than simple data types must be instantiated before they can be used (unless you test them for Nothingness).