Set A Function To Null?
Dec 5, 2011
I'm using VB Express 2010.
I have coded a function (let's call it my_boolean_function) on a form. The last line in the function returns the value, i.e.,
Return my_boolean_function.
The function performs correctly, but I get the warning:
Variable 'my_boolean_function' is used before it has been assigned a value. A null reference exception could result at runtime.
A solution to this has been discussed recently on this forum. One contributor suggested something that would mean initializing my_boolean_function to null
However, wanting to dig a bit deeper, I'm asking why does a function return value have to be initialized (to null)? Variables don't have to be yet the warning calls my_boolean_function a variable.
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Apr 3, 2009
is it possible for a VB.net function with a return type of integer to return null ?
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Apr 2, 2011
i hav two openfilefialogs(1 and 2). So i also have a listbox. the files opened with the openfiledialogs will be added to the listbox. and when i need to open the files i need to see if they are from which openfiledialog. so
it is like this.
Path.GetDirectoryName(OpenFileDialog1.FileName) & "" & Form3.ListBox1.SelectedItem.ToString
'if this returns a null then go to this
Path.GetDirectoryName(OpenFileDialog2.FileName) & "" & Form3.ListBox1.SelectedItem.ToString
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Aug 24, 2010
I am trying to write a generic function that will check each database parameter to see if it is null, and if so, return DBNull; if not, return the object.So here is my function:
Public Shared Function CheckForNull(ByVal obj As Object) As Object
If obj <> Nothing Then Return obj Else Return DBNull.Value
End Function
[code].....
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Nov 21, 2009
I have it set up so that the person hosting an event only has to copy the standardized form from a competitior's post on the forum. The basic format is as follows:
Quote:
Name
ISNAME
Gender
[Code]....
allHorses is a global 2D array for holding each horse as they're added to the roster. Right now I'm trying to get it to add the information for just one horse; once I get it worked out I'll make it dynamic and what not.
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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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Oct 2, 2009
why I am getting a NULL reference error. Form: Public Sub CreateSession() ' This will be the execution function after the date, provider, session type, session number ' and consumers have been entered. Each Consumer will have it's own tabpage and seperate record.
[Code]...
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Jun 16, 2009
.i'm having a slight problem with the following function i wrote
Dim bytes As Byte()
bytes = Convert.FromBase64String(Base64String)
However, it returns me System.OutOfMemoryException error when the Base64String contain large
[code]....
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Apr 25, 2011
I have a several form elements that I am dynamically creating with javascript when a user changes a number value in a textbox, by filling the innerHTML of a div like so:
dfinnerhtml = dfinnerhtml + "<div class='field'> ";
dfinnerhtml = dfinnerhtml + "<textarea name='textbox1" + suffix + "' type='text' id='textbox1" + suffix + "' value='' rows='4' cols='20' class='field'></textarea> ";
dfinnerhtml = dfinnerhtml + "</div> ";
Then, in the aspx.vb code behind, when the user clicks the Save button, I run through a series of Requests to try and add the values that are in these form elements to a SQL string:
Dim DFTestValue1 As String DFTestValue1 = Request("textbox" & c.ToString)
where c is a loop counter to the # of textboxes created (the input value mentioned above that triggers the create) The problem here is that this code works in Internet Explorer but not in Firefox or Chrome. The Request() value returns null and nothing is saved. I hope I've explained this well enough.
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Jun 24, 2011
In the following code an error arises because the date being passed to the cDate function is Null. However, the catch statement is in error and reports index out of range on the Catch Ex as Exception line. The exception helper says the word Exception is in error and advises that it is index out of range.
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Mar 29, 2012
I am trying to call an external C++ function using VB.NET (answers in C# are fine, I can convert back) which returns a list of device names. This comes in the form of a pointer to a null-terminated array of null-terminated char arrays (correct me if I've misunderstood what I'm dealing with) with a function signature:
long GetNames(char*** names)
Most of the answers to similar questions I've found have involved something more like:
long GetNames(char** names, int length)
It appears from what I've read that I need to give it an IntPtr but I'm uncertain as to how this should be initialized, and in my case I don't know the length of the array. At the moment, in the VB module, I have:
<DllImport("MyExternal.dll", CallingConvention:=CallingConvention.Cdecl)> _
Function GetNames(ByRef names as IntPtr) As UInteger
End Function
I've tried calling the function by passing an IntPtr initialized as IntPtr.Zero or using Marshall.AllocHGlobal, but I always get an AccessViolationException.
Any ideas on how I should be calling this function and how I get the return value into a managed string array would be greatly appreciated.
EDIT: I've found a sample function call in native C as follows:
char **tmplist;
GetNames(&tmplist)
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Feb 7, 2012
I am trying to implement a function for my SSRS report which will return a color value depending on the values of three dates.
[Code]...
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Jul 7, 2009
I am using following code in rowdatabound fn.
Protected Sub gvwMileStone_RowDataBound(ByVal sender As System.Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs)
[code]...
ddlEProjectLevels is dropdownlist in edititemtemplate.Whwn i click edit in 1st row ddlEProjectLevels gets loaded with data from database.But in 2nd row dropdownlist does not contain values.Again in 3rd it gets loaded from db.Means in alternate rows,when i click edit dropdownlist(ddlEProjectLevels) doesnot load values.Can anybody help?
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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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Aug 12, 2009
When I put a break point to the last if clause in the sub ("If (backOrder < 0) Then", see below) it runs until the break point, if I put the break point further below, I get the following error:
Cannot insert the value NULL into column 'OrderID', table 'WHM.dbo.OrderDetails'; column does not allow nulls. INSERT fails. The statement has been terminated.
I've discovered first hand that it only happens when prodqty is bigger then qtyOnStock, thus executing the if clause.
The code:
Private Sub NCOSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NCOSubmit.Click
Dim sqlText As String = ""
[Code]....
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Oct 20, 2011
I am trying to create a treeview in VB.net, the data has to be loaded from MSAccess 2010 database. When I try to run this program I get error : Argument Null Exception was unhandled, 'column' argument cannot be null and the program crashes. I have pasted the code as under:
Imports System.Data.OleDb
Public Class frmRating
Private Sub frmRating_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles
[code].....
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Oct 12, 2011
I want to make an numerical integration method with takes in an analytic function and integrate it over a specific interval. For the numerical integration procedure I want to use some procedures in nr.com. The problem is that these are programmed in C++ and they uses functors to pass a function to the integration method. How can I do this in VB 2010?
I want to initialize the function (i.e. set a=1,b=0 for function y(x)=a*x+b) and then pass the function to the integration method. Then when the integration method call the function it only calls the function with one parameter (i.e. x since a,b is already set)
What is the best way to do this in VB2010?I want to make a general integration method where I can pass any single valued function and integration limits.
I have just started using VB, and from what I have found so far it seems like the tools you have is
- to us a delegate for the function
- to use a lambda expression for the function
- send a pointer/adressOf
- to create a function class/structure and submit this to the function
As for now I am most inclined to create a function-class. But I am not really sure how.F.ex. I make different classes for each "uniqe function" I want to integrate, but how can I pass them to the integration function when I need to specify the argument type in the integration-function-call?This seems like a basic problem which applies to many Math operations, so I think it would be very useful to clarify this.
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Apr 1, 2010
I'm trying to undersatnd the syntax of calling a funciton and it seem confusing when I'm using a web service in ASP.net. Maybe this question should be in an ASP forum, but it is a VB question. This simple web service allows you to type in your name and it response with an alert box with you name.
My question is, How can you call a function with 2 arguments when the function is only defined for one. I understand that the second argument is actually a method that handling the respons, but how can you interchange function arguments for methods and how do you know that there are methods for
Here's my call:
<script type="text/javascript">
function HelloWorld()
{
var yourName = $get('txtYourName').value;
[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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May 25, 2012
I am trying to convert a DLL function call which has the Callback function routine called within the DLL function call.The DLL function call signature is like this:
typedef void *HANDLE;
typedef HANDLE HACQDESC;
DECLARE_HANDLE (HWND);
[code]....
how to convert this DLL call to VB.NET and also how to create the callback function and send it as parameter to this function
call.
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Aug 1, 2009
i wanted to ask how to make picturebox1 ,to which functions are already assigned, perform the same function as picturebox2 ,to which no functions are assigned.For example:I have already made picturebox1 and have assigned it alot of function like when play button is pressed then picturebox1.visible = true and when we press pause button picturebox1.visible = false. So now i decided to make a theme and have to remove the picturebox1 and want to allow the picturebox2 to havefunction of picturebox1.But when i disable the theme the function of picturebox1 should go back to picturebox1.
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Dec 13, 2011
I need to execute a stored function in oracle or sql through vb.net. I created a command object. Depending on the database type(oracle or SQL) i am preparing the Command text as Select functionName(?,?,?,?,?,?,?,?) from dual; (For Oracle) Adding the parameter values of the function. Now performing the ExecuteScalar which is not working saying invalid parameter. This works with ODBC connection string. But ODBC doesn't with 64bit. My Requirement: Code should execute a user defined stored procedure by taking the values at runtime.
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Feb 17, 2011
I'm currently working with a client's VB.Net code, which was developed for them by a small development shop a few years ago and which they purchased and have been maintaining and uprgrading since. This client's primary developer is out on indefinite (likely permanent) medical leave and I'm now filling in until they bring in a full timer (as I'm a contractor here). My current task is to add some functionality to a the VB.Net code they purchased. I'm finding practices and techniques in the code that absolutely baffle me and can't make the code do what I want. I'm starting to wonder if it's me and was hoping to get some thoughts on the code I've encountered.
For example: Setting a variable to accept the result of a function by calling the function with many parameters, clearing the parameters in the function, setting them to some value, calling another function with those new values, then never using the values returned by the functions. I'll add a code snippet in the first comment since this is already getting long.
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Aug 20, 2009
Hi. what is the difference of sleep function and pause function (using timer) between a loop.
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Oct 19, 2010
What does this error mean in VB6? Function or interface marked as restricted, or the function uses an Automation type not supported in Visual Basic.
I keep getting it when i call a particular method of a dll that comes with windows xp and beyond (in system32 called upnp.dll)
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Jan 25, 2010
How can I call a function from inside another function and suspend the calling function until the called function is finished? I hope I can get some replies because I don't know how to ask the question and make sense:).
Anyway what I am trying to do in steps:
1. The user clicks button1 which triggers the click event.
2. From the click event I call a function
3. I then pop-up a form, that has instructions for the user to read.
4. After the user has read the form he will click the "Done" button and return to the calling function.
The problem is the the calling function continues to execute. I want to stop execution of the calling function until the users clicks the "Done" button on the instruction pop=up. I know I can use a msgbox but the instructions can be lengthly and does not look good in a msgbox.
I have tried the Call method with return in the "Done" button click but I can make that work. I also tried a goto statement but I can get that to work either. In the call statement I said call frmInstruction.show() and it got there but as I said the calling function continued to execute.
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Jan 30, 2010
ive two custom controls, which are used to draw and edit etc...(like paint but customized....) i want to save their images with a single click....So im using the Getimageofcontrol function to do it....its code is below:::
Public Function GetImageOfControl(ByVal c As Control) As Image
Dim rc As New Rectangle(c.PointToScreen(c.Location), c.Size)
Dim i As Image = New Bitmap(rc.Width, rc.Height)[code].....
and the code to call this function for saving the images is simply.. ...
GetImageOfControl(pboxd).Save("c:78.jpg")
GetImageOfControl2(pboxf).Save("c:lp.jpg")
but the problem is that both the images have the same content....
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Sep 14, 2010
I have a function where I am performing a lot number of database operations inside a Sub. The operation when called directly like:ExecProcess()
takes about 11 seconds to run.However, if I create a Delegate, and call the sub using BeginInvoke(), the very same process takes over 40 seconds to execute.Here's the threaded code:
Protected del As ProcessDelegate
Protected Delegate Sub ProcessDelegate()
del = New ProcessDelegate(AddressOf SELocal.ExecJob)
Dim cb As New AsyncCallback(AddressOf Me.ExecJobComplete)
del.BeginInvoke(cb, del)
Anyone know what may cause a function to take longer inside a new thread, rather than calling directly?
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Jun 13, 2011
I have 1 string : abc @#ABC.xyz123ZYX
Now I need to encode the string:
The encoding alphabetic characters,
CODE:
With this string, after encoding, the result is: zyx @#ZYX.cba123ABC
About Function Encrypt and Function Decrypt?
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