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].....
Is there a way to pass an optional parameter to a webservice, instead of having to overload the method?If the webservice user is accessing the webservice directly, I want to do ActionA, if the user is accessing the webservice through my web interface, I want to do ActionA + ActionB.
View 1 RepliesHow can you set a function optional argument to null? For example, I want to set the optional argument intCode equal to Null. These arguments are used to send to a stored procedure as parameters.
Public Function pubfnc_SetCommentCode(ByVal strFieldName As String, ByVal lngResultID As Int32, Optional ByVal intCode As Int32 = DBNull.Value) As String
I have a problem during defining a Sub routine in VB.Net. I am defining a sub routine which is as under
Private Sub ActivateControls(rdbutton as RadioButton, Optional txt as Textbox, Optional txt2 as Textbox)
End sub
When I call this sub routine It gives me the Error that Each Optional Parameter must specify a default value. So, Here I can't understand that what can be the default value of a textbox. What default value I can use here to remove this error.
I am hardcoding an insert statement to a database, based on certain details a user enters into a windows form. The form has a few textbox and datetimepicker controls for the purpose. This form enters a single row in a single table in the database.The table has a few possible null columns defined, in those cases where the user does not have any data for those columns at that particular time.
I have to provide controls for passing data to those null columns nevertheless. In my case, I have two such columns that accept null values, and two corresponding controls - a textbox and a datetimepicker. The datetimepicker has a checkbox added to it so that if it is supposed to be null it doesn't pass the default current date value, and remains unchecked to explicitly specify that it is supposed to be null. By default it is unchecked.
My code is structured as follows:
Form1:
'the sub referenced here resides in a dll file in my dataaccesslayer code, and in my actual example is referenced properly.
'I have shortened the code here for simplicity
[code]....
Now it gives me an error whenever the code comes to the executenonquery(), and says something to the tune of "SqlDateTimeOverflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM."
I think the value of 'Nothing' from the subprocedure's paramter is not being assigned to the sqlcommand's parameter as a database NULL, which is what I need to pass to the database.I know instead of using optional parameters I can easily create overloaded subprocedures where one sub allows not passing values where the column(s) is supposed to null and other overloaded subs permit combinations of which column(s) are null or not. But it is simple as long as there is just one, or at the most two null columns in a table. If I have dozens of null values in a table that the user can choose to enter or not in a data entry form?
My problem is this (apologies if this is a little long ... hang in there):I can define a function in VB.NET with optional parameters that wraps a SQL procedure:
Sub Test(OptionalByVal Arg1 As Integer _
Optional ByVal Arg2 As Integer _
Optional ByVal Arg3 As Integer
[code].....
I am trying to have an optional Date value in one of my sub but since you cant set Date to nothing, this doesn't work. And i cant set it to the Date.minvalue inline.
Private Sub abc (ByVal A As String, Optional ByVal B As Date = Nothing)
End Sub
So, i went and set it to some date in the past.
Private Sub abc (ByVal A As String, Optional ByVal B As Date = #1/1/2001#)
End Sub
what would be the proper way to handle the default value for an optional Date?
I tried DbNull.Value but no luck. How do I assign a default value as null to a string parameter that is null in VB.NET? Its litte strange to see that VB does not have anything like plain null as most of the other languages do. Also what is the difference between null and DbNull and Nothing.
View 3 RepliesHow can i create a optional parameter in C# as we create in VB.Net
Public Sub Demo(ByVal a As Integer,Optional ByVal b as integer=3)
End Sub
I want to declare this in C#
[code].....
Is it possible to have an optional parameter of the type list?Ex.
Private Function TestFunction(Optional ByRef MyList As List(Of Double))
The real problem is giving the list a default value. When dimming a new list, you can use the code below to give it a starting value:
Dim MyList As New List(Of Double)(New Double() {1, 2, 3, 4, 5})
But even after trying many variations of the above code, I cannot get it to work as an optional parameter.
how can use color as an optional parameter in a sub/function?This doesn't work.
Code:
Public Sub WriteLog(ByVal sText As String, Optional ByVal lColor As Color = Color.Blue)
'Code
End Sub
I have come across something confusing or potentially a bug in Visual Studio 2010 when defining an interface in my VB application: When defining an interface method with a default parameter of type Double, using the Double.NaN constant as the default value causes the code editor/intellisense/precompiler some issues.The following code underlines "INaNTest" and "INaNTest.DoSomething" claiming that 'DoSomething' cannot implement 'DoSomething' because there is no matching sub on interface 'INaNTest':
[code]...
where now "NaN" has been divorced from the "Double." prefix and underlined ('NaN' is not declared. It may be inaccessible due to its protection level.) The code editor has inserted invalid code again.Is there a correct solution to using Double.NaN as the default value for a method as defined on an interface, in VB.net, or is there a fundamental reason why this is impossible?
Public Function Foo(ByRef a As AClass, _
Optional ByRef b As BClass = Nothing, _
Optional ByRef c As CClass = Nothing) As XClass
Error : Optional parameters must specify a default value.
I have an object, called 'PERSON' This person object has a title, firstName & Surname property as well as many other which are at the moment irrelevant. It also has a read only property called Fullname which concatenates the two or three parameters mentioned above depending on an optional parameter 'withTitles' passed over when you call PERSON.FULLNAME
PERSON.FULLNAME(true) <- Will add titles if there are any
PERSON.FULLNAME(false) <- Will give the name without the title
Public ReadOnly Property FullName(Optional ByVal withTitle As Boolean = False) As String
[Code]...
I get an error: PERSON does not contain a property of 'FullName'. If I change this to any other property that does not take a parameter it works as expected. Now I'm guessing that the binding procedure can't handle optional or mandatory parameters for object properties, is this right? Is there a better way to do it? I thought about looping through the collection to add them manually but that kinda defeats the object of DataBinding!
I have traditionally coded empty strings like this "", but for a couple of years now, I have been using String.Empty.I also normally never use optional parameters, but I'm refactoring a solution that's tied into my ERP, and I don't want to break anything. One of the changes was to add a parameter to proc, which pushes a new parameter into the method from which it is called. I coded it like this:
Optional BackReferenceID As String = String.Empty
But I got a syntax error "Constant expression is required." I guess String.Empty is non-deterministic??? Anyway, it seems like a bug. The workaround is of course to use double quotes.
I tried the following, but i get the error
constant expression is required
Public Sub ExampleSub(ByVal Test as string,
Optional ByVal fromDate As System.Nullable(Of DateTime) = Date.Today)
'A Great sub!
[Code].....
How can I create a nullable numeric optional parameter in VB.NET?
View 3 RepliesI am using Stanav's PdfManipulation2.AddImageToPage(..., Pages) for iTextSharp library (v5.1.3) and was not able to add the image to specific pages: e.g. to add to only page 1 and 3 of a five pages PDF
Dim Pages() As Integer
Pages = New Integer() {1, 3}
PdfManipulation2.AddImageToPage(..., Pages)
Calling AddImageToPage() with the the optional Pages parameter will add the image to all pages though.
I just got upgraded from VB6.0 to VB2010. I'm trying to move some of my program functions over and I'm getting an error on the ones where I use optional... Public Function GetFolder(ByRef FTT As String, Optional InitFile As String)
I get the error at the end of the line, after the close par...the error is "optional parameters must specify a default value".
I want to pass an optional parameter to a function of type System.Drawing.Color. The problem I am having is that when I declare the function it says "Constant expression is required" but I have tried variations of the following, including integers, full qualified indentifiers, even old vbWhite constants to no avail.
[Code]...
I am calling a crystal xi report from a windows form and passing 2 date parameters and a customer name. In some cases this customer name contains '&' eg Brown & Williams
In these cases my report fails and errors. if the name doesn't contain '&' it works. How can I pass the parameter with a & in it ?
I am getting an error when I write a value to the database. it tells me "Key cannot be null. Parameter name: key". However the key is an auto-increment value and i'm not even writing to that field. I have verified that there is a value being sent to the SQL. I also created a seperate program that writes the same SQL statement to the db and it writes just fine. I also have other places within the same program that write to the database without any problems.[code]
View 17 Repliesi'm having some problems here.i try to put in some data into sql server by using vb code. the data types are small integer and unsigned tinyint.i would like to assign the value as NULL instead of '0' because my reading takes 0 and 1.i tried in this way.
Dim Ignition As Integer = Nothing
Dim ADCCount1 As Integer = Nothing
Param = New SqlClient.SqlParameter("@Ignition", Ignition)[code].....
when i viewed my sql table i found that the Ignition and FuelRead1 show 0.previously i tried to set the value to NULL but it showed error.What should i assign the ignition and ADCCount1 so i will obtain NULL in database?
Following is the code where i am getting the "Value cannot be null. Parameter name: Key" exception.
I cant see anything wrong in this code.
ReadOnly Property dvMeasurements() As DataView
Get
Dim dvMeasurementsRet As DataView = Nothing
[Code]....
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.
View 4 RepliesI created a dataset that is getting data from an access database. Now i would like to go further and make the dataset query accept a parameter from a form datepick value. the query in my table adapter I have changed it as follows to accept a parameter on date1.[code]The code I am using in my form is as below. I get a null reference exception on the second line(Object reference not set to an instance of an object). it seems as if my selectCommand is bringing nothing.[code]
View 4 RepliesI have a bound DataGridView (dgvBuild) that contains data based on a "ProductID" that is derived from selecting the value from a ComboBox. How do I pass the ComboBox Value to the DataAdapter to retrieve records to reload the dgvBuild? Below is the code for theDataAdapter.This is the line that was created when I bound the DataGridView to a DB Table.
View 8 RepliesI need to pass an event as a parameter to a function and I'm wondering if there is any way of doing this.The reason why I need to do this is because I have a sequence of two lines of code that is littered all over my program, where I dynamically remove the handler to an event, then set the handler again. I'm doing this for several different events and event handlers, so I've decided to write a function that does this. As an example, let's say I have a combobox in my code called combobox1, and I have the handler called indexChangedHandler. In several places of my code, I have the following two lines:[code]Now, I don't want to keep on repeating the above two lines of code (or similar) all over my program, so I'm looking for a way to do this:[code]So far, the "evt as Event" part of the argument of the setHandler function is giving an error. Any ideas on the right way to do this will be very welcomed.
View 2 RepliesI need to pass an event as a parameter to a function and I'm wondering if there is any way of doing this.
The reason why I need to do this is because I have a sequence of two lines of code that is littered all over my program, where I dynamically remove the handler to an event, then set the handler again. I'm doing this for several different events and event handlers, so I've decided to write a function that does this.
As an example, let's say I have a combobox in my code called combobox1, and I have the handler called indexChangedHandler. In several places of my code, I have the following two lines:
RemoveHandler combobox1.SelectedIndexChanged, AddressOf indexChangedHandler
AddHandler combobox1.SelectedIndexChanged, AddressOf indexChangedHandler
Now, I don't want to keep on repeating the above two lines of code (or similar) all over my program, so I'm looking for a way to do this:
Private Sub setHandler(evt As Event, hndler As eventhandler)
RemoveHandler evt, hndler
AddHandler evt, hndler
End Sub
so that everywhere where those two lines of code(or similar) occur in my program, I can just replace them with:
setHandler(combobox1.SelectedIndexChanged, AddressOf indexChangedHandler)
So far, the "evt as Event" part of the argument of the setHandler function is giving an error.
P.S I've asked this question on a couple of other forums and keep getting asked why I would want to set the handler immediately after removing it. The reason is because dynamically adding an event handler n-times causes the handler to be executed n-times when the event occurs. To avoid this, i.e to ensure that the handler is executed just once when the event occurs, I first remove the handler each time I want to add the handler dynamically.
You might be asking why the handler would be added several times in the first place... The reason is because I add the handler only after a particular event, say E1, in my form has occured (I add the handler within the handler of event E1). And event E1 can occur several times within my form. If I do not remove the handler each time before adding it again, the handler gets added and thus executed several times.
Whatever the case, the processing occuring within the function is not of ultimate importance to me at this time, but rather just the means of passing an event as a parameter.
I'd like to create a function myFunc with one parameter, which is a delegate. I should be able to call it with a delegate as parameter.E.g.[code]But how do I code myFunc, in other words, how do I enable myFunc to have it passed a delegate so that it can be called using myFunc(addressof test Func)?
View 4 Replies