I am trying to dequeue items if they contain a certain string. This is the idea I was hoping would work but does not:
Dim baseUri As String = myuri.GetLeftPart(UriPartial.Authority)
For i = workerURLs.Count - 1 To 0 Step -1
If workerURLs(i).Contains(baseUri) Then
workerURLs.Dequeue(i)
End If
Next
Since the queue method has no "Dequeue at index" option like a list would how can I accomplish this?
One way to implement it would be to wrap a Queue(Of T) and recreate it when an element gets "dequeued" from the middle:
Class IndexableQueue(Of T)
Private _queue As New Queue(Of T)()
Public Sub Enqueue(item As T)
_queue.Enqueue(item)
End Sub
Public Function Dequeue() As T
Return _queue.Dequeue()
End Function
Public Function Dequeue(index As Integer) As T
Dim list = _queue.ToList()
Dim item = list(index)
list.RemoveAt(index)
_queue = New Queue(Of T)(list)
Return item
End Function
End Class
This is the simplest implementation although it's not the most efficient as we are recreating the Queue on every call to Dequeue(Integer). But if it's uncommon and the queue is not massive it should be fine.
The best way would be to completely reimplement the Queue and use a List instead of an array as underlying type.
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.
How do i loop through this class once I add items via this method. Just I am quite new to generic lists so was wonding if someone could point me in right direction in datatables im used to doing the following:
For Each thisentry In dt.rows
Next
What do I use in collections
Calling Code
Calling this in my delciarations of main class
Dim infoNoProductAvail As List(Of infoProductsNotFound) = New List(Of infoProductsNotFound)()
this is how i am adding the files but I have checked in the routine and the count for the list is at 2 products
If medProductInfo.SKU.SKUID = 0 Then
infoNoProductAvail.Add(New infoProductsNotFound(thisenty2.Item("EAN13").ToString(), True))
End If
this is the class itselfs
Public Class infoProductsNotFound
Public Sub New(tbcode As String, notfound As Boolean)
Me.tagbarcode = tbcode
Me.notfound = notfound
End Sub
Private tagbarcode As String = String.Empty
Private notfound As Boolean
Public Property tbcode() As String
Get
Return tagbarcode
End Get
Set(ByVal value As String)
tagbarcode = value
End Set
End Property
Public Property isNotFound() As Boolean
Get
Return notfound
End Get
Set(ByVal value As Boolean)
notfound = value
End Set
End Property
End Class
Tried
I tried using the following
Function BuildExceptionsForEmail()
Dim retval As String = ""
Dim cnt As Int32 = 0
retval = "The following products are not avialable" & vbCrLf
For Each info As infoProductsNotFound In infoNoProductAvail
retval &= info.tbcode
cnt &= 1
Next
Return retval
but for some reason at this point my info noproductAvail is blank even though in the routine above its sitting at count of 2 what gives?
First I'd shrink that declaration a bit:
Dim infoNoProductAvail As New List(Of infoProductsNotFound)
Next, to iterate there are several options. First (and what you're likely most used to):
For Each info as infoProductsNotFound in infoNoProductAvail
If info.tbCode = "xyz" Then
DoSomething(info)
End If
Next
Or you might want to use lambda expressions (if you're using .Net 3.5 and above I think - might be .Net 4):
infoNoProductAvail.ForEach (Function(item) DoSomething(item))
Remember that generics are strongly typed (unlike the old VB collections) so no need to cast whatever comes out: you can access properties and methods directly.
If infoNoProductAvail(3).isNotFound Then
'Do something
End If
(Not that that is a great example, but you get the idea).
The For Each syntax is the same. It works the same way for all IEnumerable objects. The only "trick" to it is to make sure that your iterator variable is of the correct type, and also to make sure that you are iterating through the correct object.
In the case of the DataTable, you are iterating over it's Rows property. That property is an IEnumerable object containing a list of DataRow objects. Therefore, to iterate through it with For Each, you must use an iterator variable of type DataRow (or one of its base classes, such as Object).
To iterate through a generic List(Of T), the IEnumerable object is the List object itself. You don't need to go to one of it's properties. The type of the iterator needs to match the type of the items in the list:
For Each i As infoProductsNotFound In infoNoProductAvail
' ...
Next
Or:
Dim i As infoProductsNotFound
For Each i In infoNoProductAvail
' ...
Next
Or:
For Each i As Object In infoNoProductAvail
' ...
Next
Etc.
i have 20,000 items in a queue, and i want to process them using the threadpool.
will this be the best way to do it?
for i as integer = 0 to 19999
ThreadPool.QueueUserWorkItem (PerformTask, ListTask(i))
next
Sub PerformTask(i as string)
' do the work here
end sub
How can i return or set ui control from the PerformTask sub?
You cannot.
However, you can allocate a container (array, list) with a different slot for each result, and write into it. Alternatively, you could pass an object into the worker method that holds both the input and the result. I’d use this method:
Class TaskObject
Dim Input As String
Dim Result As Whatever
End Class
Dim tasks As TaskObject() = New TaskObject(20000) { }
For i as Integer = 0 to tasks.Length - 1
ThreadPool.QueueUserWorkItem(PerformTask, tasks(i))
next
Sub PerformTask(arg As Object)
Dim task As TaskObject = DirectCast(arg, TaskObject)
' do the work here
end sub
Unrelated: you should always enable Option Strict in your projects. No exception. Your code has type errors that the compiler should detect.
Rather than giving the very specific case (which I did earlier), let me give a general example. Let's say that I have a function, called callingFunction. It has one parameter, called parameter. Parameter is of an unknown type. Let us then say that I wish to copy this parameter, and return it as a new object. For example, in pseudo code, something along the lines of...
Function callingFunction(ByVal parameter As Object) As Object
Dim newObj As New Object
'newObj has the same value as parameter, but is a distinctly different object
'with a different reference
newObj = parameter
return newObj
End Function
EDIT: Additional Information
The first time I posted this question, I received only one response - I felt that perhaps I made the question too specific. I guess I will explain more, perhaps that will help. I have an ASP page with 10 tables on it. I am trying, using the VB code behind, to come up with a single solution to add new rows to any table. When the user clicks a button, a generic "add row" function should be called.
The difficulty lies in the fact that I have no guarantee of the contents of any table. A new row will have the same contents as the row above it, but given that there are 10 tables, 1 row could contain any number of objects - text boxes, check boxes, etc. So I want to create a generic object, make it of the same type as the row above it, then add it to a new cell, then to a new row, then to the table.
I've tested it thoroughly, and the only part my code is failing on lies in this dynamic generation of an object type. Hence why I asked about copying objects. Neither of the solutions posted so far work correctly, by the way. Thank you for your help so far, perhaps this additional information will make it easier to provide advice?
You can't do this in general. And it won't be a good idea, for example, if parameter is of a type which implements the singleton pattern. If parameter is of a type which supports copying, it should implement the ICloneable interface. So, your function could look like this:
Function MyFunc(ByVal parameter As Object) As Object
Dim cloneableObject As ICloneable = TryCast(parameter, ICloneable)
If Not cloneableObject Is Nothing Then
Return cloneableObject.Clone()
Else
Return Nothing
End If
End Function
You could implement something like this:
Dim p1 As Person = New Person("Tim")
Dim p2 As Object = CloneObject(p1)
Dim sameRef As Boolean = p2 Is p1 'false'
Private Function CloneObject(ByVal o As Object) As Object
Dim retObject As Object
Try
Dim objType As Type = o.GetType
Dim properties() As Reflection.PropertyInfo = objType.GetProperties
retObject = objType.InvokeMember("", System.Reflection.BindingFlags.CreateInstance, Nothing, o, Nothing)
For Each propertyInfo As PropertyInfo In properties
If (propertyInfo.CanWrite) Then
propertyInfo.SetValue(retObject, propertyInfo.GetValue(o, Nothing), Nothing)
End If
Next
Catch ex As Exception
retObject = o
End Try
Return retObject
End Function
Class Person
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
Here's a simple class that will work for most objects (assumes at least .Net 2.0):
Public Class ObjectCloner
Public Shared Function Clone(Of T)(ByVal obj As T) As T
Using buffer As MemoryStream = New MemoryStream
Dim formatter As New BinaryFormatter
formatter.Serialize(buffer, obj)
buffer.Position = 0
Return DirectCast(formatter.Deserialize(buffer), T)
End Using
End Function
End Class
Having a bit of trouble using the List.Find with a custom predicate
i have a function that does this
private function test ()
Dim test As Integer = keys.Find(AddressOf FindByOldKeyAndName).NewKey
here's the function for the predicate
Private Shared Function FindByOldKeyAndName(ByVal k As KeyObj) As Boolean
If k.OldKey = currentKey.OldKey And k.KeyName = currentKey.KeyName Then
Return True
Else
Return False
End If
End Function
by doing it this way means i have to have a shared "currentKey" object in the class, and i know there has to be a way to pass in the values i'm interested in of CurrentKey (namely, keyname, and oldkey)
ideally i'd like to call it by something like
keys.Find(AddressOf FindByOldKeyAndName(Name,OldVal))
however when i do this i get compiler errors.
How do i call this method and pass in the values?
You can cleanly solve this with a lambda expression, available in VS2008 and up. A silly example:
Sub Main()
Dim lst As New List(Of Integer)
lst.Add(1)
lst.Add(2)
Dim toFind = 2
Dim found = lst.Find(Function(value As Integer) value = toFind)
Console.WriteLine(found)
Console.ReadLine()
End Sub
For earlier versions you'll have to make "currentKey" a private field of your class. Check my code in this thread for a cleaner solution.
I have an object that manages a list of Unique Property Types.
Example:
obj.AddProperty(new PropertyClass(PropertyTypeEnum.Location,value))
obj.AddProperty(new PropertyClass(PropertyTypeEnum.CallingCard,value))
obj.AddProperty(new PropertyClass(PropertyTypeEnum.CallingCard,value))
//throws exception because property of type CallingCard already exists
Here is some code to check if properties already exist
Public Sub AddProperty(ByVal prop As PropertyClass)
If Properties.Count < 50 Then
'Lets verify this property does not exist
Dim existingProperty As PropertyClass = _
Properties.Find(Function(value As PropertyClass)
Return value.PropertyType = prop.PropertyType
End Function)
'if it does not exist, add it otherwise throw exception
If existingProperty Is Nothing Then
Properties.Add(prop)
Else
Throw New DuplicatePropertyException("Duplicate Property: " + _
prop.PropertyType.ToString())
End If
End If
End Sub
I haven't needed to try this in newer versions of VB.Net which might have a nicer way, but in older versions the only way that I know of would be to have a shared member in your class to set with the value before the call.
There's various samples on the net of people creating small utility classes to wrap this up to make it a little nicer.
I've found a blog with a better "real world" context example, with good variable names.
The key bit of code to Find the object in the list is this:
' Instantiate a List(Of Invoice).
Dim invoiceList As New List(Of Invoice)
' Add some invoices to List(Of Invoice).
invoiceList.Add(New Invoice(1, DateTime.Now, 22))
invoiceList.Add(New Invoice(2, DateTime.Now.AddDays(10), 24))
invoiceList.Add(New Invoice(3, DateTime.Now.AddDays(30), 22))
invoiceList.Add(New Invoice(4, DateTime.Now.AddDays(60), 36))
' Use a Predicate(Of T) to find an invoice by its invoice number.
Dim invoiceNumber As Integer = 1
Dim foundInvoice = invoiceList.Find(Function(invoice) invoice.InvoiceNumber = invoiceNumber)
For more examples, including a date search, refer to Mike McIntyre's Blog Post