VB Check For Null Reference When Passing ByRef?
Jun 6, 2011
I have a function that accepts a String by reference:Function Foo(ByRef input As String)
If I call it like this:
Foo(Nothing)
I want it to do something different than if I call it like this:Dim myString As String = Nothing Foo(myString) Is it possible to detect this difference in the way the method is called in VB .NET?All the logic is in the second overload, but I want to perform a different branch of logic if Nothing was passed into the function than if a variable containing Nothing was passed in.
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Dec 8, 2009
I am making use of a 3rd party dll and am encountering some strange behavior in VB, which doesn't occur in C# Perhaps someone can explain what is going on. Anyhow, I am making use of a method in this 3rd party library which accepts an array parameter ByRef. The end result is the variable should remain null after the method call, but it is returning initialized for some reason.
[Code]...
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Jun 24, 2010
I have some code which gets child items for a menu via the GetChildren function which takes a list of menuData: Dim builtMenu As New List(Of MenuData)(_rawData.FindAll(Function(item) item.GroupingID = 0))
For Each menuData As MenuData In builtMenu
If menuData.Children IsNot Nothing Then
menuData.Children.AddRange(GetChildren(menuData))
End If
Next
If I check if menudata.children isnot nothing, it always is nothing because the GetChildren function is yet to run (providing the child items, which do exist). If I remove this check and just have this code:
Dim builtMenu As New List(Of MenuData)(_rawData.FindAll(Function(item) item.GroupingID = 0))
For Each menuData As MenuData In builtMenu
menuData.Children.AddRange(GetChildren(menuData))
Next
Then I am presented with a Object reference not set to an instance of an object error on menuData.Children.AddRange(GetChildren(menuData))
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Oct 11, 2011
I am trying to develop a .NET class that updates a VB6 Form and its controls with various new captions (It is in an assembly that is COM visible).
I pass a VB6 form ByRef as an object to the .NET class and then update the caption etc on the form as follows:
Public Sub AddFormRefLegacy(ByRef objForm As Object)
Try
objForm.Caption = "some new caption"
[Code].....
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Jul 23, 2010
I have been working on this for a few days, and I am going around in circles. I can make the program work by including everything in the same sub procedure, but the assignment requires that I do certain tasks by using function procedures.What I need to do is take the contents of a text box, reverse the order of the first and last names, and add them to a list box. I can do that, just not by passing value from a function procedure. Here is my
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Jan 31, 2012
I am trying to create a Library for like code that we use in more than one application. One call involves an array where I need to create a pointer to the array for what I need.
Is there a way to pass a value ByRef, have it increment, and return the value back to the original call?
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Jul 22, 2010
Reading [URL] made me wonder whether the comments in there did apply to Strings in terms of performance. Since strings are copied before being passed, isn't it much more efficient (if the callee doesn't need a copy of string course) to pass strings ByRef?
[Code]...
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Jan 9, 2010
I have a C# interface defined as so:
public interface IMenuSecurityService
{
void SetSecurityFlags(List<MenuItem> items);
}
I need to implement this interface in a VB.Net class. When I implement the SetSecurityFlags method with the items parameter passed ByVal, it compiles.
Public Sub SetSecurityFlags(ByVal items As List(Of L1.Common.Model.MenuItem)) Implements IMenuSecurityService.SetSecurityFlags
' do some work
End Sub
When I try to implement it with the items parameter passed ByRef, I get the following compiler error: Class 'UserRights' must implement 'Sub SetSecurityFlags(items As System.Collections.Generic.List(Of Model.MenuItem))' for interface
Public Sub SetSecurityFlags(ByRef items As List(Of L1.Common.Model.MenuItem)) Implements IMenuSecurityService.SetSecurityFlags
' do some work
End Sub
I can't seem to figure this one out. Does VB.Net not support this or am I doing something wrong?
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Dec 31, 2009
This is the code:
Public Class userDefClass
private b as integer = 1
End class
Public Class Form1
private SomeClass as new userDefClass
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) [Code]...
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Sep 14, 2010
In VB6.0, you could create a sub that took an array byref, and then call it with an argument that was an indexed element of the array, and it would treat that index as the starting point. This was very useful, for example, if you were trying to create a binary string to send over a communication port.The same thing doesn't work in VS 2008,Let us say for example I have the following Sub:
Public Sub HexToAddr(ByRef addr() As Byte, ByVal addrstr As String)
Dim i As Integer
For i = 0 To 7[code]....
Is there some tricky way to make this work, or do I really have to either (a) create a completely separate array of bytes, call the function, and then copy the data, or (b) create a completely separate version of HexToAddr which takes an "offset" argument for the destination array?
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Jun 29, 2009
I create tabpages at runtime each having a flexgrid controls. I need to pass these flexgrids of each tabpage as a parameter to a function byref. This is the code .
[Code]...
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Dec 22, 2010
I have some code that is transforming the coordinates of a line.I want to keep the original coords and I thought passing the line ByVal would be the best way.The original VB6 code used a temporary variable so that the original coords were not updated.I'm confused as when the X & y coords of 'line' are changed 'MyLine' is also changed. I had assumed only 'line' would change and 'MyLine' would remain unchanged'.
Private Sub TransformSaveLine(ByVal MyLine As LineType)
Dim P As Integer
Dim line As LineType
Dim x As Double
[code].....
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Mar 15, 2011
I am experimenting with more effective ways to generate forms. My experiments goes into the possibility to link strings, and other types, directly by their class reference and use it to update the original values without any strongly typed code.
I have been using GCHandle.AddrOfPinnedObject to get the memory address of the string, but it gives the the memory address of the string data, not the string class/reference that i need to change to allow me to use this approach.I am aware that strings are immutable and can not be changed (Actualy, you can, but its not recomended), but I do not want to change the actual strings, but change the reference to it (the string object).Is there some other way to get the address of a string object reference?
[Code]...
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Dec 15, 2011
I have a fairly simple piece of code:
Private _PurchaseDelivery as PurchaseDelivery
Protected Overrides Sub InsertItem(ByVal index As Integer, ByVal item As PurchaseDeliveryItem)
[Code]....
Which is inside a class which overrides a custom list base. The code is occassionaly throwing an unhandled exception, System.NullReferenceException, on this line when used in production:
If _PurchaseDelivery IsNot Nothing AndAlso _PurchaseDelivery.DefaultSKUBinID.HasValue Then
DeafultSKUBinID is declared as an Integer? (Nullable Int) in the PurchaseDelivery class. I cannot see what might be causing this error, why would this be returning an error?
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Jul 15, 2011
How to check whether a column is null i use the following code but I got this error "Input string was not in a correct format."
[Code]....
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Sep 27, 2010
I have code, shown below, that works all except for 1 thing: The variables being passed byRef get passed, but once modified in the else section of the "if me.invokerequired" code of RecordData, the variables are never updated in the calling function. To reiterate, the calling function does not receive the updated data that is in the variables custid and amt.When debugging, I see the data change in the else section of "if me.invokerequired", but once it returns from the callback the data is missing.[code]
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Jan 12, 2011
I'm using an interop dll in a VB.NET project to get access to some functions in a MFC project.
Dim bIsSupposedToWork As Boolean = True
Dim api As API = GetObject(, "MyProject.API")
[CODE]...
Why?
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Feb 8, 2011
I have a function that takes in a number of parameters.. it then does a db insert.i have a foreign key on one of the fields (modelID)i want to pass a NULL if no model ID is selected.[code]but now i get an error saying: Nullable object must have a value.if i pass in a 0, it does not insert because it breaks the DB constraints.
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Jul 20, 2010
I have a Function within a data access layer, which accept a number of parameters. Among these is a decimal value, but in some cases the decimal value with be NULL, here is the code from the function
I am using the following code in my code file to pass the value to the function...
Convert.ToDecimal(textbox1)
How can I pass a NULL value to my function?
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Sep 22, 2010
I think this is a pretty basic question, but I just want to clarify. If I have a variable with a null value, and pass it as a parameter that is optional, will the parameter get the null value, or the default value?
dim str As String = "foo"
dim obj As Object
//call 1
[code].....
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Apr 9, 2012
i have a stored procedure to insert data into table create procedure insertdata
[Code]...
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Mar 25, 2009
i'm not 100% sure about sql server but i think it doesn't accept null value for date type columns but in oracle, a date column can accept a null value. and since i'm using oracle, this is causing some problems because in my form, a textbox item bound to a date column will not accept a null value. reading thru some threads, it would seem that it is not possible to pass a null value to a date type in .Net.
[Code]...
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Jun 2, 2010
This is related to my previous question but it is a different problem.I have two classes: Server and Database.
[Code]...
The problem is in the LoadTables in the Server class. When it hits Databases.Add(db) it gives me a NullReference error (Object reference not set). I don't understand how it is getting that, all the objects are set.
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Jan 8, 2011
I have been trying to use sockets in VB.NET and once I cannot understand how to avoid a null reference. [code] I have tried introducing sock as 'New Socket', but this gives me 'Overload resolution failed because no accessible New can accept this number of arguments'.I also cannot simply add '= Nothing' onto the end of my declaration since this still gives a null reference.
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Jan 29, 2011
I'm practicing on this one, and I know it would be better to just use a string variable instead of a class. I have another working program using a string variable, but on this one I wanted to make it use an array of class objects.
I keep getting null reference exceptions at the line where the object is assigned the textbox text.[code...]
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Dec 16, 2010
How do I check for a null object in a subroutine handle?
Private Sub Form1_KeyDown( _
ByVal sender As Object, _
ByVal e As System.Windows.Forms.KeyEventArgs) _
[code]......
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Mar 21, 2011
I have a null reference warning. Dummy code as follows:
Dim poo As IEnumPooTypes
Toilet.GetPooInBowl(poo)
The variable 'Poo' says it may result in an object reference not set error but I cannot use the 'New' keyword with an instance. How do I make the warning go away?
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Jun 27, 2012
visual basic application prompting me a message "Object reference not set to an instance of an object". i have 2 project in one solution. One is developed in c# and other is in vb. i am calling a method of c# project in vb project. the vb code is:[code]when i debug vb project individually it works properly and when i call vb application from c# application, it prompting error. is i missed out any .net framework reference? [code]
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Jan 4, 2010
Im trying to write code that will insert 'records' into an xml file, but everytime i click the button to make the changes to the XML file, it throws a null reference exception, ive gone through this code must be 100 times and cannot find what needs to be declared as 'new' as i know nodes can't be 'new' and the doc is 'new'
Imports System.Xml
Public Class frmuseradmin
[code]......
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Jul 19, 2011
Let's says I have a class called Customer :-
Code:
Dim Cust as New Customer("Fred")
I also have a function in a seperate class :-
Code:
Shared Function Example(Example As Customer)
How do I refer to the class itself from within itself? For example :-
Code:
' from within the Customer class, call the Example function
AnotherClass.Example(Me??)
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