.net - Using Child Classes Polymorphically With Differing Return Types?
Apr 10, 2012
I have two Parser classes that inherit from a base class, BaseParser. I want to use either class as a parameter in another Monitor class. The Parser classes, CS600 and TCH600, both have two properties, RawDataList and SummaryDataList. The CS600 class's RawDataList returns a List(of CS600Data); the TCH600 RawDataList returns a List(of TCH600Data). The SummaryDataList returns similar classes in each Parser class. CS600Data and TCH600Data derive from a base class, BaseData.BaseParser also has RawDataList (List(of BaseData)) and SummaryDataList (List(of BaseSummaryData))The Monitor class has a private field, _thisParser which can be either of the two concrete Parsers above. I want to be able to call and use RawDataList and SummaryDataList of _thisParser within Monitor class, but when I construct the concrete Parser classes, Visual Studio notes that the RawDataList property of CS600 cannot override the RawDataList property of the BaseParser because they differ in their return types.
I thought that since CS600Data derived from BaseData (but also adds some new properties of its own) that I could use CS600Data wherever I use BaseData. What am I misunderstanding? How can I correctly construct these classes?
Public MustInherit Class BaseParser
Protected _rawDataList As List(Of RawGasData.BaseData)
Public MustOverride ReadOnly Property RawDataList() As List(Of RawGasData.BaseData)
[code]....
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Jun 9, 2009
I have two objects that are derived from same the base class. ets say ObjA is the base class, and ClassB and ClassC inherits ObjA. f I have a dim lst1 as List(Of ClassB) im list2 as List(Of ClassA)nd and I want to check for the existence of something being in lst1 that it is in list2, now I am only interested in comparing against one key bit of information that it is declared in the base class and is a string. How can I iterate through the lst1 comparing against list2? I thought I could I overload/override the Equals method but I am having no joy for either of the classes and say some thing similar to
Public Overloads Overrides Function Equals(ByVal obj As Object) As Boolean
Dim temp As ClassA = TryCast(obj, ClassA)
If temp.Id = Me.Id Then
[code].....
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Sep 16, 2009
I'm studying for the MCTS exam 70-536 and have come across the following question:Given the following Visual Basic code sample, which interface must the custom class MyClass implement?
Dim a As MyClass, b As Boolean
a = 42
' Convert using ToBoolean.
b = Convert.ToBoolean(a)
Console.WriteLine("a = {0}, b = {1}", a.ToString, b.ToString)
Before even looking at the possible answers, I can't get past WHY on earth would we be converting the number 42 to a Boolean value?? I tried this and as I suspected it did NOT compile! Is this a trick question or am I missing something? I realized that in order for the code to work, I would need to implement one of the interfaces shown in the multiple choices. STILL, would there EVER be a purpose for this particular conversion?
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Jan 3, 2012
I have a nested class, let's call it class1 and it has class2 inside it; VB.Net eg:[code]
1) How can I define X number of Class2 objects[let's call it: Node(x) array]** with NEW() subroutine called?' this raises error: dim cls2(n) as new class2 end sub.
2) How can I return actual number of Node() array? [code]Outside my class in main project I define cls1 object:[code]Now an array of class2 is created inside cls1.
3) Now,How can I access All of them[node(x) array which is created inside cls1] with all properties and methods available?
I remember I wrote a ProcessManager class with this functionality in .net 2003, nearly 4 years age, I don't have the code now.
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Sep 5, 2009
Assuming Anonymous Types are tailored to be used with LINQ, I'd like to use them for simply and fast data aggregation without an explicit class definition, like in this snippet[code]....
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Jul 7, 2011
I have a program with a base class and classes that inherit the base. A Windows Form will call a function of each child class which raises an event from the base class. The function call to the first child class works fine: the event is raised for the first child class.
[Code]...
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Feb 17, 2012
So you know how PHP internal functions usually return a boolean FALSE when a function fails, or some other data type when the function succeeds? Is this possible in VB .Net?For instance, lets say this simple code here Public Function TrySomething(ByVal Param As String) \what would go here??
[Code]...
You see I want to return a BOOLEAN false when a function fails, and a string when the function works. I've looked everywhere, and when I search for "return multiple types" all i find is Tuple.
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Dec 26, 2010
I have a Clients master object and then a number of child objects whose exact number is not known in advance such as Client-Contacts, Client-Payments etc, all of which have a one-to-many relationship with the Client master object.How do I define classes for such a scenario? Do I for instance create the master Clients class and can then I create an array of class somehow for child objects?
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Feb 29, 2012
I remember seeing somewhere on the net that there are classes in .Net that will return information about your computer. I know that System.Environment returns some of this information like MachineName and some other stuff. Are there other classes that will return information such as hard drive size, free and used space, total memory, used memory?
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Aug 13, 2009
When attempting to create a UserControl type that must be inherited, when I try to edit one of its child classes in the Form Designer, I am not allowed to edit the child UserControl with the message:
To prevent possible data loss before loading the designer, the following errors must be resolved:
1 Error
The designer must create an instance of type "XX_ExpandContentsPanel2.IOCardMaster", but it cannot because the type is declared as abstract.
This error goes away if I remove the "MustInherit" restriction.Is there some way around this or do I just have to accept the (bonkers-mad) restriction, and not declare my class as as MustInherit, even though it's not a useful control in its own right?
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May 12, 2010
I need to provide a DLL that is consumed by a VBA app (Access 2003, late binding) and returns stuff that is retrieved from various WebServices. These WebServices publish methods that not only return a single object, but also arrays of them.
From the Access-app's point of view, it's no problem to consume i.e. an array of strings. However, there's also methods that return an array of a (proprietary) class. I can't seem to be able to consume such an array from VBA.[code]....
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Jan 25, 2010
I have the following statement, I want to turn it into a Public Shared Function :
If isEmployee Then
Dim employeeInstance As New Employee
employeeInstance = GetEmployeeInstanceByUserId(userId)
[Code]....
Public Shared Function GetWorkerInstance(Byval isEmployee as Boolean) As ...(not sure what to write here)...
There two possible return Type. I'm not sure what I should declare for the function return type.
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Jun 8, 2012
Lets say I click a button on a form that calls a function in a data access class. This function inserts a record into a table in a database. The function returns an integer value for the record id of the newly inserted record. Now lets say the insert failed (syntax error, timeout, whatever). I can return a zero to the calling routine to indicate the failure, but not the error message. So in general, what's the most appropriate way to handle getting information back to a calling routine when the return parameter data type doesn't allow it?
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Aug 18, 2011
We are developing a webservice for a client. We are not supose to throw SoapExceptions, so instead, we catch every exception server side, and return a custom Exception class.
Public Class Order
...
End Class
[Code]....
The problem now is, that since my webmethod is returning the type [Object]. The wdsl that is generated does not contain the order, or the exception.
I can change the [Object] to [Order] Or [MyException], but only one of them is generated in the wsdl.
I want both the MyException type and the Order type in my wsdl, but i just cant get it working.
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Aug 16, 2010
I have such a bad habbit of cramming all my code into one form. But i dont know when i should write a class. or dont really understand how to return the information back to form1. when should i even use a class? for example i have some code here
[Code]...
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Jul 21, 2009
I've just been burned again by the fact that there is no compiler warning when you fail to return a result in a Function that returns a Value type. I wrote the function:
Public Function CompareTo(ByVal other As MessageIndex) As Integer Implements System.IComparable(Of MessageIndex).CompareTo
Me._messageIndex.CompareTo(other._messageIndex)
End Function
which performs the CompareTo Function for two integers, then throws the result away and returns 0, because I forgot to either assign a value to CompareTo, or use Return, and that isn't flagged by the compiler because it's valid VB for a Value type.
I happen never to use "FunctionName = ReturnValue" because it hides information from maintenance programmers and also because I think it's insane .
Is there any way I can get the compiler to issue a warning whenever my Functions are missing a Return, whether it's a Value type or not?
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Dec 10, 2011
I have a parent class that is also a factory. For example:
Public Class Factory
Public Function clone() as Factory
' Some logic here
[code].....
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Jul 17, 2010
way to return a collection of treenodes which are children of a selected node? I can't find on MSDN a object of treenodes that is a collection of childnodes.
I have two treeviews, and I am writing code that will copy treenodes from one treeview to another treeview if it is selected. If a parent node is selected, I would also like to copy over all the children. If it is just a childnode, then I would like to copy just that.
Here is what I have so far.
Dim treeobj As TreeNode
treeobj = TreeView2.Nodes.Add(TreeView1.SelectedNode.Text)
If TreeView1.SelectedNode.Parent.Index.ToString Is System.DBNull.Value Then
[Code]...
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Mar 5, 2010
At the moment I'm trying to create a kind of model in vb.net which can be used to create/fetch database entrys.
I created a main class Model with a shared function to fetch the datasets, e.g. Model.find(). Now I'd like to create Classes which inherit the main Model-Class, e.g. a separate one for users: UserModel.find() => "SELECT * FROM users".
What I need now is to find a way to tell the Class which table it should use. I thought about an abstract String "table" which is a constant in each "child-model", but how could this be implemented as it's not possible to override shared members?
Edit: Maybe this will make it a little clearer what I mean:
Public Class Model
Public Shared _controller As Controller
Public Shared table As String
[Code].....
So I want a shared method which finds all database entries and gives back an array of instances of its own type, e.g. Model(). That's why I wanted to keep the find-method shared and not bound to an instance.
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Jan 1, 2012
I have Class1 and class2 which is inside class1, VB.NET code:
Public Class class1
Public varisbleX As Integer = 1
Public Class class2
[code]....
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Mar 9, 2009
how to loop through a zip file and return all the file extensions in the zipped file.
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Feb 18, 2011
Im working with MDI parent/child objects. when closing the child objects i need the child to check to see if it is the last child object before closing. i couldn't find anything on google, maybe im searching for the wrong thing.
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Apr 15, 2010
I have a slight problem With an enumaration of child controls on a form. The following code will not get but about have the controls that are on the form. The controls show that the count is correct but when it goes through the loop it skips over some of the controls. If you run it through the enumeration two or three times it will get all the controls a few at a time. The solution uses two forms, one that has the controls and the other that labels are made and displayed on. The Tx is just a index to add a number to the label.name and rename the label. So each label is identified seperately. This works for all the the controls that are seen in the for each loop.
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Nov 1, 2009
I have a class with a Property called 'Value' which is of type Object.Value can be of any type, a structure, a class, an array, IList etc.My problem is with the setter and determining whether the value has changed or not.This is simple enough for value types, but reference types and lists present a problem.For a class, would you assume that the Equals method has been implemented correctly, or just assume that the value has changed every time the setter is called?If I did assume it's changed, then perhaps I should assume it for value types as well, so that the behaviour is consistent.
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Jan 23, 2012
I have two classes, one nested in the other. [code]Neither "Name" or "ID" are unique between operations and records.I wish to construct a dictionary using LINQ = Dictionary(Of String, Of List(Of Integer), whereby the keys are uniqe examples of Names in my collection and the values are the collective set of distinct IDs that are associated with those names.
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Jun 13, 2012
How can I structure my classes so that the user interfaces though a single class while the supporting classes are hidden from their view? I think its best understood in an example:
Public Class MyInterface
Public Economic as EconomicClass
Public Sub New()
MyBase.New()
[code].....
So you might ask why am I even separating them? It's strictly for others who will be working with this interface. I need to funnel them though a logical structure:
interface.Economic.MyMethod
interface.Currency.MyMethod
etc
This way everything is already handled for them in the background and they only need to run the method they need. I don't know if I can have it both ways in VB.NET.
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Oct 24, 2009
Here is some example code of what I mean:
vb
Public Class Form1
Private Sub Button1_Click(ByVal sender as Object, e as systemEventArgs) Handles Button1.Click
[Code]....
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Jul 10, 2009
I m trying to raise Click event of Textbox explictly but I m getting "Derived classes cannot raise base classes" error.[code]....
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Jun 23, 2012
I need to compare two dictionary values if the types stored are equal, this is what i have
if gettype(Args(key)) = gettype(argtypes(key)) then
'' do something
end if
[Code]....
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May 21, 2012
Dim obj_DataTable As New System.Data.DataTable("Category")
Dim obj_DataSet As New DataSet()
'Declaring the array of DataColum to hold the Primary Key Columns
[code].....
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