Assign Nothing To The Structure And Not To Its Members
Jul 2, 2010
I'm having some headaches using Structures and functions that return Nothing in VB.NET. [Code] In the previous code, when I return Nothing as result of Foo function I'd expect that st is Nothing. But this is not what happens. Then I found in MSDN documentation: Assigning Nothing to a variable sets it to the default value for its declared type. If that type contains variable members, they are all set to their default values.
So I discovered that when I assign Nothing to a structure, all its members are set to their default values, instead of the structure itself.
Also, I tried to make st a Nullable type by declaring: Dim st As Nullable(Of Test) = Foo()
but, still I can't check if st is Nothing by using: If st Is Nothing Then
or If st.Equals(Nothing) Then
So, questions:
1 - Is it possible to assign Nothing to the structure and not to its members?
2 - How can I check if a return structure value is Nothing?
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Jun 21, 2010
i've created a 2-dim image array but cannot assign images its members. i have done as follows
[Code]...
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Aug 11, 2009
In VB.NET, why can't I see a member of a structure when I make it a nullable type?
Example:
Public Structure myNullable
Dim myNullVar As Integer
End Structure
Sub Main()
[Code]...
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Oct 12, 2010
In Vb.net I am trying to assign an array of structure to another array of same structure[code]...
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Dec 5, 2011
I have a structure written in vb.net with all shared members. I need to override 'Equals', '==' and '!=' to avoid a warning.
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May 1, 2009
I am trying to figure out how to print specific members of a structure when I only have to pass the structure itself i.e.
Dim Point1 as PointF = New PointF(15,30)
Debug.Print(Point1) ' This will output "{X = 15, Y = 30}" by default
I am trying to figure out how I can do the same with my own strucutres, for example:
Dim Point2 as PointF2D = New PointF2D(15,30)
Debug.Print(Point2) ' This will output "ClassName.PointF2D.Point2"
How can I get my structures, when passed to a print statement, to print specific members of that structure by default? P.S. Please give another way other than overloading the .ToString function.
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Jul 15, 2011
how you init a variable when it is created by assigning the value on the same line in which it is declared. Is there a way to do this with members of a structure?
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Jan 19, 2012
When it comes to constructors in a Structure type ,it is fact that we can not explicitly provide the default constructor .It is provided by the runtime. Ok, another point that is applicable to C# language is that if we are defining a parametrized constructor then it is compulsory to initialize all fields . We can not leave any field uninitialized , since the runtime will not call default constructor if we are calling parametrized constructor .Its logically right , but in VB.NET language , actually you are free to leave any of the fields uninitialized in your parametrized constructor.
[Code]...
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Mar 2, 2010
I have a main array that is a structure with three fields which consists of id_code(int)members(int) and annual_income(dec). I've get everything entered and I want to go to a procedure that prints a report giving the total percentage of families below a particular income and the level is different depending on how many members there are in the family.
Option Strict On
Public Class Form1
[code].....
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Aug 19, 2011
I have a user defined structure in a list that I am trying to change the value for in an individual element within the list of structures. Accessing the element is not a problem. However, the compiler complains
"Expression is a value and therefore cannot be the target of the assignment"when I try to update the value.For example:
Public Structure Person
Dim first as String
Dim last as String
Dim age as Integer
[code]....
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Jan 5, 2010
ok this is annoying, i've got a structure RInteger.
Private VAR_Value As Integer
Private VAR_Max As Integer
Private VAR_Min As Integer
[code]......
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Jan 5, 2012
Module Module1
Public Structure structure1
Public TRANS() As structure2
End Structure
Public Structure structure2
Public X() As Integer
End Structure
End Module
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Jan 5, 2010
I'm new to VB 2008 after having spent a long time with VB6, so I apologize if this is a stupid question. But I'd really like to have this straightened out.
Let's say I have a pretty large structure that has lots of properties.
Code:
Now say that I want an internal database with about 10 instances of this structure total, describing, say, 10 different products that a store sells. When these values are loaded from a database, they remain totally static. (However, they can be different each time a program loads)
Now say that I have a class. Each instance of this class is a type of that BaseProduct structure. Meaning, each instance of the class pertains to one of the 10 types of products that the store sells. However, this class has additional properties that pertain specifically to each instance, which are not static.
Code:
Now, the problem here is... If I have 200 different transactions, each one contains an instance of BaseProduct. BaseProduct is HUGE, and is largely redundant (only 10 types possible), so I think it's a little silly to include a whole copy of it with EVERY transaction. However, the Transaction class really needs information regarding the base product it pertains to. Is there a way to, instead of declaring a New BaseProduct in the Transaction class, to simply make one of the properties of the Transaction class a pointer to a BaseProduct variable?
In VB6, I would accomplish this by making a BaseProduct(10) array, and then giving each Transaction an ID number referring to an entry in that array. But in VB 2008, using class structure, this is impossible. I can't define the BaseProduct(10) array outside of a class in a namespace, and if I define it in the actual application's form, then the class loses modularity since it relies on the application that's using it.
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Aug 29, 2009
I am trying to communicate with an external device and i am trying to send a byte array to the external device via sockets but i am always getting a response the message size is too small so i am not sure what i have done wrong. Between the data type there should be no alignment present and all numbers are represented in little endian format. The char array is not null terminated as mentioned in the protocol specifications.
I have to send data based on a struct that embeds 2 other struct. So here's my vb.net code for the struct used to convert to byte array and the sending part.
Public Structure MESSAGETYPE_OIP_Login
Dim Header() As COMMANDHEADER
Dim UserName() As PSTRING
[Code]....
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Mar 9, 2010
Admin assigns the authority and get a new form to the new assign in with vb.net & access. I am not sure about this,I need a way to do the new form assigned? How?Actually, this project is the admin will assign the authority to a manager, and the manager will get the password to log in. Then, the manager once log in and will get a form to set the rooms who is going to use and date, etc, this is multi-manager to handle the room setting jobs.But, I think, I got stuck, I am not sure how to do the new form, HOW DO YOU ASSIGN THIS NEW FORM FOR EACH NEW MANAGER?????? THIS IS VB.NET WITH ACCESS.
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Apr 14, 2012
I'm experiencing a problem with the following c-structure:
typedef struct tagTEXTUREPROP
{
DWORD dwSize;
[Code].....
The Marshal.SizeOf obviously calculates a size of 76 and it works with the DLL function, but it leaves me with some bad feelings.
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Apr 25, 2010
I'm having a problem that's driving me crazy; I can't understand how to convert the XML structure into a class structure (that I want to use to hydrate a XML document).
The XML document looks like this:
xml
<?xml version="1.0" encoding="utf-8"?>
<artists xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/" xmlns="http://www.spotify.com/ns/music/1">
[code]....
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May 23, 2010
I want to make a structure within a structure. Basically it will appear like this:
Structure ID
dim CardType as string
im CardCode as string
[code]......
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Oct 24, 2011
Im trying to search the entire active directory to look for a group and then see if the current logged on user is listed, then take an action based on that result.So far i have the below code which doesnt return the users who are members of the group MyTestGroup. Could anyone assist or guide me to see how i achieve this?
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Sep 12, 2011
I have two structrures
Public Structure PhoneScheduleEntries
Dim Count As UInteger
Dim PhoneSchedule() As PhoneScheduleEntry
End Structure
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Nov 29, 2010
According to this post the code below should compile, while it is not.
class Base
protected m_x as integer
end class
[code].....
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Oct 25, 2009
I migrate between C++ and VB.NET in my coding ventures... which leads to the occasional confusion about when something is by value or by reference in VB.NET.Let's say for example that I have an array of MyObject which is populated with a bunch of objects.
dim MyArr(5000) of MyObject. let's say that the information from this array travels throughout various data structures:
dim MyList as new List(of MyObject)
for i as integer = 0 to 5000 step 1000
Mylist.add(MyArr(i))
next
Under the above scenario, I believe everything is by reference. If I extract an entry from "MyTable" and modify its MyObject Members, I think that the original in MyArr will be modified.However, I have run into situations where I thought something was by reference, and it was by value. Are items always added to containers by reference, or are they sometimes added by value?
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Apr 16, 2010
I'm trying to change the data binding of a listbox when the value of a combo box changes.Here is the ComboBox change code - [code]...
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Jan 23, 2011
According to a mspress book (MCTS for Exam 70-536 .NET 2.0): You might have version compatibility issues if you ever attempt to deserialize an object that has been serialized by an earlier version of your application. Specifically, if you add a member to a custom class and attempt to deserialize an object that lacks that member, the runtime will throw an exception. In other words, if you add a member to a class in version 3.1 of your application, it will not be able to deserialize an object created by version 3.0 of your application.
Now... As curious as I am I went and created a project, serialized a class, added a new member and attempted to deserialize the class to the new object. To my surprise it worked and the newly created member was set to null by default (even if it had another default value).
[Code]...
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Oct 25, 2010
I wrote some code to add the Name and Value to Combobox.
dt = New DataTable
dt.Columns.Add("Name")
dt.Columns.Add("Value")
[Code]....
Now i want to enumerate all the ValueMemer (11,22,33,44) and all the DisplayMember (AA,BB,CC,DD) from Combobox1, how to do?
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Nov 23, 2010
i have to develop API in .Net 4.0 which can be used in VB 6.0,i know how to use this and currently i am using my this API in VB successfully.but Stuck at one place,i have collection class and i have to expose it to VB with having functionality of List class of .Net.[code]i know that generic is not supported in VB, but i think with this declaration in VB 6.0 it creates interface class for class B as IList.but in VB using object creation of class B it doesn't provides me members of LIST in intellesense like (Add,Remove of List Class)
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Jun 7, 2011
How to list Enum's members in code? I have following Enum:
Public Enum TestEnum As int32
First = 0
Second = 2
Third = 4
Fourth = 6
End Enum
And I try to list all members of TestEnum via following code but it failed:
Public Class Form1
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
[Code].....
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Jun 22, 2010
Why does intellesense show shared members? e.g:Dim x as doublex.epsi 'Epsilon will show up as a valid member in intellesenseIs there a way to change this behavior?
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Apr 21, 2010
When I pass an an object 'MyObject' which implements 'IMyInterface' to a method parameter declared as IMyInterface, I understand that this method parameter 'sees MyObject through the eyes of its interface'.
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Jun 4, 2011
I have an EggSac object which contains references to >100 000 Egg objects. Some variables in the Eggs have to be maintained to be consistent with EggSac, so I want to make these only changeable by EggSac. However EggSac passes references to its Eggs all over the application, so if I use public methods then any other code could modify the secure parts of the Eggs by accident.
What's a proper OO way to make sure only the EggSac object can call the "secure" methods of the Eggs, but still make the "safe" methods available to everyone?
My idea is to split Egg's class into a base class containing only safe methods and a derived class containing the secure methods that only EggSac should have access to. Then EggSac has members of the type of the derived class, but it casts them to their base class whenever something else wants one.
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