XmlSerializer(Type) Constructor Throws ArgumentNullException
Dec 27, 2010
I've been having problems with following code on some computers, while it's worked super on others (most):
Dim xmlSer As New System.Xml.Serialization.XmlSerializer(GetType(XMLContext))
which produces the stacktrace:
System.ArgumentNullException: Value cannot be null.
Parameter name: type
at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
How can that code throw that exception, when the argument is drawn from a gettype call, and note that it doesn't happen when debugging on my own PC, only when it's installed on some of the client PC's???
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Mar 19, 2012
I wish to put the XMLSerializer behind a 'facade' class of mine so that user wont have to supply type info to the constructor. But doing this has a problem. Consider this class:
Class XmlFormatter
Private Shared xs As XmlSerializer
Public Function Deserialize(ByVal serializationStream As Stream) As Object
Dim o As Object = Nothing
[code]....
The problem is that the user of this class cannot use Deserialize without first using Serialize because the XMLSerializer instance is created in Serialize and it is shared. But using Deserialize without this instance will simply return Nothing.
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Jan 31, 2012
why this gives an error at run-time:
Dim mightBeNothing As List(Of String) = Nothing
Dim a As List(Of String) = IIf(mightBeNothing Is Nothing, New List(Of String)(), New List(Of String)(mightBeNothing))
I am getting ArgumentNullException on the second line. If I replace the last part with:
Dim a As List(Of String) = IIf(mightBeNothing Is Nothing, New List(Of String)(), New List(Of String)())
It works - but the constructor New List(Of String)(mightBeNothing) will never be called if mightBeNothing is nothing, so what is the issue?
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Jan 15, 2009
I'm trying to serialize a user's preferences by means of an XMLSerializer. The preferences class contains Strings, Integers, Booleans and several Color structure variables. The serialization doesn't throw any errors, however the generated xml file has empty values only for the color variables.I tried the following two declarations of the XMLSerializer object, neither workerd.
[Code]...
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Feb 3, 2011
Is there any way to create an XmlSerializer that stores along with the serialized data the data type, then when deserializing, it automatically identifies the type of the serialized object and creates an object of that type (returned as object).
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Mar 7, 2011
What I want to do is pass a Type to another object's constructor, where the other object creates a new instance of Type. I can create a constructor with a parameter declared as System.Type without problem, but when I try to instantiate it tells me there is no such type.
Public Sub New(targettype As System.Type)
Dim Test As System.Windows.Forms.Form = New targettype
End Sub
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Nov 26, 2010
How do I get using reflection the most generic type from a shared constructor in the base class :
Public Class Foo()
Shared Sub New()
'Here we have code to get the type[code]....
I expect the result to be Bar type and not the Foo. Is it possible?
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Jun 18, 2012
I have this code to get the default constructor:
Public Function f(ByVal t As System.Type) As Object
Return t.GetConstructor(New System.Type() {}).Invoke(New Object() {})
End Function
I need to pass values to the Constructor as
Public Function f(ByVal t As System.Type) As Object
Return t.GetConstructor(New System.Type() {someInteger,someString,etc.etc}).Invoke(New Object() {})
End Function
Also I have 3 classes of Type T, with all having different parametric constructor. It's important for me to have it generic as the Classes of type T might increase in future with less or more parameters.
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Jan 29, 2010
I'm passing a type name and some parameters from C# code into a navigation framework written in VB. The navigation framework looks for a constructor on the type that matches the parameters passed in using Type.GetConstructor(Types()). The constructor that I'm looking for expects an array of integers Integer() in vb. But it gets an array of System.Int32. I've gone so far as to try this:
[Code]...
And the VB code still sees System.Int32 on the other end, which means that it doesn't find the constructor.
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Jan 5, 2011
After debugging a particularly tricky issue in VB.NET involving the order in which instance variables are initialized, I discovered that there is a breaking discrepancy between the behavior that I expected from C# and the actual behavior in VB.NET.Nota bene: This question concerns a slight discrepancy in the behaviors of VB.NET and C#. If you're a language bigot that is unable to provide an answer other than "that's why you should use C#, noob", there is nothing for you to see here; kindly move along.Specifically, I expected the behavior outlined by the C# Language Specification (emphasis added):
When an instance constructor has no constructor initializer, or it has a constructor initializer of the form base(...), that constructor implicitly performs the initializations specified by the variable-initializers of the instance fields declared in its class. This corresponds to a sequence of assignments that are executed immediately upon entry to the constructor and before the implicit invocation of the direct base class constructor. The variable initializers are executed in the textual order in which they appear in the class declaration.
Contrast that with the portion of the VB.NET Language Specification concerning Instance Constructors, which says (emphasis added): When a constructor's first statement is of the form MyBase.New(...), the constructor implicitly performs the initializations specified by the variable initializers of the instance variables declared in the type. This corresponds to a sequence of assignments that are executed immediately after invoking the direct base type constructor. Such ordering ensures that all base instance variables are initialized by their variable initializers before any statements that have access to the instance are executed.
The discrepancy here is immediately obvious. C# initializes class-level variables before calling the base constructor. VB.NET does exactly the reverse, apparently preferring to call the base constructor before setting the values of instance fields.If you want to see some code, this related question provides a more concrete example of the divergent behavior. Unfortunately, it does not provide any hints as to how one might coerce VB.NET into following the model established by C#.
I'm less interested in why the designers of the two languages chose such divergent approaches than I am in possible workarounds for the problem. Ultimately, my question is as follows: Is there any way that I can write or structure my code in VB.NET to force instance variables to be initialized before the base type's constructor is called, as is the standard behavior in C#?
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May 10, 2010
I got 2 classes in a form, and I would like to pass a value from a textbox to the other class, so I decided to use Deligate.
Below is the code.
Public Delegate Sub delPassSize(ByVal text As TextBox)
'To get size from Class Calculate(Class 2)
Public Sub GetSize(ByVal txtForm1 As TextBox)
[code]....
and the error message is 'cls.Getsize is a delegate type and requires a single 'addressof' expression as the only argument to the constructor.'
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Feb 15, 2010
I have an abstract class which requires a delegate to function. I pass the delegate into the constructor. Now that I have a non default constructor I need to call the abstract class's constructors from the concrete class which means that I need to use MyBase.New(...). I have included a quick example below.
Public MustInherit Class BaseClass
Public Delegate Sub WorkMethod()
Private _Work As WorkMethod
[code]....
I have tried to do this but I keep getting the following error: "Implicit reference to object under construction is not valid when calling another constructor".Can I not do what I am trying to do above? I initially had the delegate setup in its own setter method. But then I am creating a deceptive API because it does require a point to a method to work properly.
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Nov 2, 2009
what's the rationale behind this limitation: Constructor call is valid only as the first statement in an instance constructor i want to pass an argument to my constructor which validates this argument and calls mybase.new according to this argument but it doesn't let me
example:
Public Class prob
Inherits System.ApplicationException
Public Sub New(ByVal problem As String, ByRef inner_exception As Exception)
[code]....
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Aug 10, 2010
I have written an MDI text Editor and I have written a "save" sub routine, please see below
'This sub routine updates the current document or calls the save as routine
Private Sub SaveToolStripButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SaveToolStripButton.Click, SaveToolStripMenuItem.Click
[code]....
I am testing this sub routine today and it throws up an error during runtime when a new document is created and the user (me in this case) writes a few lines of text, I click the save toolstrip button and because its a new document, the save as sub routine is supposed to be be invoked, however the application stops running and I get this error message "ArgumentNullException was Unhandled" from Visual Basic.
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May 17, 2010
[code] I'm basically trying to see if a record already exists. My problem is when I run this I get a "ArgumentNullException was unhandled" error It occurs on the line "dbAdapter.Fill(output)" in the sub.
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Feb 3, 2010
I am using 2005 and I am getting a ArgumentNullException when I try and debug my program. I have included the error and a piece of the code. I am not sure how to fix this error at all. If more of the code is needed I can post it.
Public
Class MainForm
Dim sPIServer As String 'PI Server Connection Storage Variable
Dim myServer As PISDK.Server 'Variable to hold the server to work on[code].....
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Jan 5, 2011
i have an ASP.NET page which has a numebr of user controls within it. There are 2 user controls which are of interest. I need to display either one of them or neither of them, depending on the record selected previously.
In the user controls I need to set properties of some controls which are in a FormView. So in my user control code-behind I have a number of properties which look something like this:
[Code]...
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Feb 25, 2011
I'm getting the following exception when I try to run up my Winforms app and haven't been able to find a solution to it:
System.ArgumentNullException was unhandled
Message=Value cannot be null.
Parameter name: activationContext
[code]....
I've added a handler for the "unhandled error" event in the applicationevents class but it never reaches that stage and there is no source code running that I can break into and diagnose.
The application was fine until I added a user control (nothing fancy, just a standard windows user control) and then dragged it onto a form in the app (user control and form were in the same application). The application builds and compiles without any errors or warnings but when I attempt to run it up I get the above error straight away.
Does anyone have any idea what it could be or even how I can go about investigating it? I'm a bit stumped on this one as I'm not sure how to investigate it. I removed the user control from the form and then I removed the user control from the application entirely but the error hasn't gone away. In all honesty the addition of the user control might be a red herring but the problem manifested straight after adding it.
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Apr 15, 2010
I have not yet tested this..but before I do that, I am just wondering, let's say you have a byte stream, and you want to deserialize that into an object?[code]...
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Oct 15, 2009
I am using the XMLSerializer to create an XML Schema. In one part of the XML, I have an element called 'parameters', which returns a collection of strings. The output is supposed to look like this:
[Code]...
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Aug 24, 2010
0I Have a vb6 application that uses .net objects via COM. When one of this objects calls code which instantiates XmlSerializer vb6 aplication crashes.Just this line fails: Dim x as new XmlSerializer(GetType(CustomClass))I agregate that these objects load assemblies dinamically but only it crashes over vb6 aplication. In .net 100% aplication this not happens.
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Jul 11, 2009
Why won't XMLSerializer process my generic list?
Sub Main()
Serializing()
End Sub
[Code]....
I get an exception on the "Dim ser" line, saying "Testing.Module1 is inaccessible due to its protection level. Only public types can be processed." ("Testing is the name of the application, and "Module1" is the name of the module; this is a console application).
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May 26, 2010
I have a custom class that has one property as a collection.For some reason XmlSerializer doesnt like the class having a collection property and the Serialize Fails!If I remove the collection property it works! Is there a special way of getting the collection in the class to work?
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Apr 8, 2011
I am trying to deserialize an Xml file content into a specific object. Everything runs fine but when I include empty tag of type date or time in my xml(having xsd that describes my xml structure) the deserialization fails. What can I do to make deserialization working when empty date tags are appear?
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Dec 8, 2011
I have the following class which I want to serialize to XML:
[Code]...
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May 6, 2012
I use DataGridView in my project. Everything worked fine until I added some code in the RowValidating event. During the form_load event exception is thrown on the statement that set the datasource of the DataGridView.The project uses bindingsource for the datasource of the DataGridView. My validating code is shown below:
Dim currentRow As DataGridViewRow = Me.dgExpenditure.Rows(e.RowIndex)
Dim incexpCell As DataGridViewCell = currentRow.Cells(0)
If Not Me.closingBoolean Then
[code]....
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Apr 24, 2011
I debated whether or not to ask in the database section, but decided this was probably more of a VB question, than DB.I'm performing a query on my database and add its value to a DGV. At the moment, I'm just running tests to make sure the base example works so I can expand on it for more advanced tests.[code]It doesn't matter how I add the row, just adding it causes the error. And yes, the AllowUsersToAddRows property of the DGV is set to True, which wouldn't cause this problem anyway, but I decided to be extra careful.
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Jan 14, 2011
I am using a dataset to pull data from a DB. One of the fields in a row is NULL. I know this. However, the following vb.net code throws a StrongTypingException (in the autogenerated get_SomeField() method in the dataset designer):
If Not IsDBNull(aRow.SomeField) Then
'do something
End If
According to documentation and this question it should be fine.
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Nov 14, 2009
i want to run a query and use the result for something else in my vb.net code. I have, opened the connection, passed the query and the connection object to the SqlCommand object and read it with the datareader object. The DataReader's HasRows property's value evaluates to true but i get an InvalidOperationException when i want to access the results of the query with the DataReader.[code]
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Jan 17, 2011
I'm currently building an application in C#, using a basic design I came up with in VB.net for applications involving openGL. Using the Tao framework in VB, I have the following method:
Private Sub checkForGlutInit()
If glut_initialized = False Then
Glut.glutInit()
[code].....
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