C# - Nullable Types And Properties With INotifyPropertyChanged?
Jan 17, 2010It seems like overkill to set the value of a nullable type and implement iNotifyPropertyChanged. Is there a better way of doing this?
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Use INotifyPropertyChanged With Auto-properties?
Jul 27, 2010Is there a way to use INotifyPropertyChanged with auto-properties? Maybe an attribute or something other, not obvious to me.
public string Demo{
get;set;
}
For me, auto-properties would be an extremely practicall thing, but almost always, I have to raise the PropertyChanged-event if the property value has been changed and without a mechanism to do this, auto-properties are useless for me.
Add Together Two Nullable Types?
Aug 27, 2010I have: Dim nVar1 As Long?Dim nVar2 As Long?Dim nVarSum As Long?nVar1 = Nothing nVar2 = 5 nVarSum = nVar1 + nVar2 I would prefer the result to end with nVarSum being 5, instead of Nothing. I understand if you add something to an unknown value, you will end up with "somthing + unknown" or x+5 will always equal "x+5" not "5" because you are still carrying around that unknown "x". However, how can I effectively treat an unknown or Nothing as a zero for the purposes of addition in this case?(What is basically happening is that the end user is sending us a data file, this code parses that file and then sums together about 15 fields. If the user leaves those fields blank instead of assigning a zero to them, I need to treat it as if it was a zero for this one addition operation, but all the rest of the code needs to continue seeing it as a Nothing value since the user did not ACTUALLY submit zero... they submitted blank or nothing)
View 3 RepliesCan Nullable Types Be Used
Jun 27, 2012Can Nullable Types be used in VB.NET? If so, is it possible to have a Nullable Integer that I can use with a field that accepts NULL in SQL Server?
View 4 RepliesHow To Use Nullable Types
Aug 25, 2010I'm converting an Access VBA app to VB.NET. It has dates defined as variants or objects to handle null values. I thought this would be a great chance to use the Nullable type. But I can't get it to work. Either it is inappropriate for what I am trying to use it for, or I am doing it wrong. Anyone know how to use it? Reader is a SqlDataReader.
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I was hoping I didn't have to put a lot of If .. Null statements throughtout the code, but that is my only option unless someone has any other idea.
C# 'AS' Equivalent For Nullable Types
Feb 15, 2011C#'s 'as' keyword will let you do this: int? input = value as int? Here's what I would assume the vb.net equivalent would be: Dim input As Integer? = TryCast(value, Integer?) There's an intellisense error in the TryCast stating the operand must be a reference type but Integer? is a value type.
Intellisense on Nullable(Of Integer) says 'Represents an object whose underlying type is a value type that can also be assigned null like a reference type.' It seems C#'s 'as' handles this like a reference type where TryCast doesn't have this built in. In VB10 I was able to take advantage of the new CTypeDynamic function to do the casting. Conversion.CTypeDynamic Method
Dim input As Integer? = CTypeDynamic(Of Integer?)(value)
Or:
Dim input As Integer? = CTypeDynamic(Value, GetType(Integer?))
There's a cost here as CTypeDynamic examines the type at runtime.
My question is what is the elegant way to handle this without CTypeDynamic?
C# 'AS' Equivalent For Nullable Types?
Nov 15, 2011Dim input As Integer? = TryCast(value, Integer?)There's an intellisense error in the TryCast stating the operand must be a reference type but Integer? is a value type.Intellisense on Nullable(Of Integer) says 'Represents an object whose underlying type is a value type that can also be assigned null like a reference type.'It seems C#'s 'as' handles this like a reference type where TryCast doesn't have this built in.
View 1 RepliesC# - Insertion Of Nullable Types Into Database
Aug 24, 2011I have recently been working on a number of sections of code that deal with the insertion of Nullable types into a database. As I'm sure anyone who has dealt with similar code will be aware of the annoyance of constantly writing conditional logic to deal with the insertion of nulls into a database. I.e.:
MyValue.HasValue ? MyValue.Value : DBNull.Value;
If(MyValue.HasValue, MyValue.Value, DBNull.Value)
Basically I am just wondering why DBNull.Value exists and why Null simply couldn't be used?
Compare Nullable Types In WHERE Clause Of Linq To Sql .NET?
May 4, 2012I am trying to query for records where that column IS NULL:
Dim UnassignedSubSvc =
From c In CurrentContext.SubService
Where c.Product.ProductSubServiceId **is null**
Select c).ToList()
Difference Between Using .GetValueOrDefault(0) And If(variable, 0) With Nullable Types?
Mar 9, 2010Is there any difference between the 2 methods below for calculating c ... specifically boxing/unboxing issues?
Dim a As Integer? = 10
Dim b As Integer? = Nothing
Dim c As Integer
' Method 1
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Error Querying When Nullable Types In Where Clause
Mar 1, 2012I have the following NHibernate Linq query:
From eachLine In myNhSession(Of SamplePoco)()
Where eachLine.SampleIntField = 1234
The property SamplePoco.SampleIntField is type Nullable(Of Int32)
When I run the query, I get the following exception:
System.InvalidCastException: Unable to cast object of type 'NHibernate.Hql.Ast.HqlCoalesce' to type 'NHibernate.Hql.Ast.HqlBooleanExpression'
If I change the property type to Int32, it works. It seems that Nullable types are automatically converted into a coalesce expression by the Linq compiler.
Debugging the NHibernate, I just found out that this Where clause was converted into: {where ((eachLine.SampleIntField == 1234) ?? False)}. As I can understand, the whole condition comparison was translated to be coalesced instead of just the Nullable property.
If I put this way eachLine.SampleIntField.Equals(1234) it doesn't work as well ('Equals not implemented' exception)
If I change the query to the following code, it works:
From eachLine In myNhSession(Of SamplePoco)()
Where {1234}.Contains(eachLine.SampleIntField)
Another code that works as well (coalescing the field properly as I was expecting by the first query):
From eachLine In myNhSession(Of SamplePoco)()
Where If(eachLine.SampleIntField,0) = 1234
Properly Use Nullable With Numeric Types In Constructors?
Jan 9, 2011I have a class that implements a range of numbers....call it NumericRange(Of T). Internally, NumericRange stores T as a Nullable, T?. I have another class that wraps this class as NumericRange(Of UInt16). Call this class MyNumRange (I'm being simplistic here). So In MyNumRange, I have a few constructors defined:
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Use Coalesce With Db Column Values And Nullable Types?
Dec 8, 2011I'm trying to do something similar to what's described here, but with nullable types.
[URL]
int availableUnits = unitsInStock ?? 0;
In VB, it would be this:
Dim availableUnits As Int32 = If(unitsInStock, 0)
However I'm working with db columns, which could be DbNull, and nullable types, which can be Nothing (which is different to DbNull). If a column is DbNull, I want to return Nothing, otherwise return the value. For eg:
Dim availableUnits As Int32? = If(myDataReader("UnitsInStock").Value, Nothing)
The error I'm getting is "Specified cast is not valid" but I'm not sure why. I've tried this as well:
Dim availableUnits As Int32? = If(isDbNull(myDataReader("UnitsInStock").Value), myDataReader("UnitsInStock").Value, Nothing)
Which is messy and just results in the same error. The only thing that works is this:
Dim availableUnits As Int32?
If isDbNull(myDataReader("UnitsInStock").Value) Then
availableUnits = myDataReader("UnitsInStock").Value
Else
availableUnits = Nothing
End If
Which is just silly. Is there a better way of getting nullable db values into nullable variables that I'm not aware of?
VS 2008 BLL - Nullable Types And Crystal Reports .Net
Jul 21, 2011I'm using my data objects in a crystal report. The thing is, when I select my object, it gets added to the field explorer table. My properties are listed except for the Nullable Type properties. Why would this happen. I've had quite a few issues yesterday as this is my first attempt at a crystal report in .Net. I thought I worked around them but now I've hit this snag.
View 11 RepliesC# - Get A Technical Reason For No Implicit Conversion From DBNull To Nullable Types?
Jan 10, 2012Is there a technical reason why there is no implicit conversion from DBNull to the various nullable and/or sql types? I understand why the conversions don't currently happen, but don't understand why an implicit conversion wasn't created at the time or added in subsequent versions of the framework.Just to be clear, I'm looking for technical reasons, not "because that's they way they did it" or "I like it that way".
View 2 RepliesDB/Reporting :: Crystal Reports & Entity Framework 4 With Nullable Types
Jul 6, 2011I have written an application which manages some bookings, and want to use Crystal Reports to provide the reporting engine. I have used it before with datasets with no problems.
I am using EF4, and have a LINQ query and report datasource assignment as below:
Code:
Dim ActiveCustomers = From Customer In FMEntities.Customers
Where Customer.Status = 1
Select Customer
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I have read up that I may need to convert the incoming data, but I am confused as to what it needs to be converted to. Should it be a datatable?
OrderBy Nullable Properties In A Generic List Throwing InvalidCastException?
Jun 13, 2012I need to return an a generic list in the correct order for my project, and I'm getting InvalidCastException errors. Here is the code:
Dim lDt As List(Of Comment) = RemapCommentsForE1(so.CommentList). _
OrderBy(Function(x) x.CreateDate.Value). _
ThenBy(Function(x) x.Sequence). _
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Cast Value Type To Nullable Enumeration Type In Generic Object If All Types Are Unknown At Write-time?
Dec 14, 2011I have a generic Class I'm using to hold information loaded from a database.I have a method which takes a DataRow as an argument, uses the object's known column name and extracts the data from the DataRow, such that:Dim loadData As T = CType(myDataRow("myColumnName"), T))works as my default assignment in most cases.Unfortunately, due to some horrifying design constraints, some of my columns may be null, and may also be taken from enumerations.This means that when <T> is Nullable(Of SomeEnumeration) the above code does not work because I can't cast 0 directly to SomeEnumeration.Zero.Is there some way to check whether <T> is Nullable(Of [Enum])? Or some way to write a method which allows Integers to be cast to Nullable(Of [Enum])?I feel like I'm forgetting something that would allow me to write one of the other of these, but my weak google-fu is turning up nothing.
EDIT: Okay, thanks to dasblinkenlight's answer below, I can detect when this circumstance is occurring, but what I need to do now is to take a type <T> which I know is Nullable(Of SomeClass), get a type reference to SomeClass and then create a new object of type Nullable(Of SomeClass) and assign that to LoadData.My problem was that I had a lot of difficulty in finding any function which would accept baseType as an actual Type.Parse accepted baseType as a parameter, I knew baseType was an [Enum] type because of dasblinkenlight's code, so I was, in this instance, able to code a solution. It's a solution which is very specific to my problem (i.e., T is Nullable(of SomeEnumeration)), but it's a solution nonetheless.
Error - Soap Serializer Does Not Support Serializing Generic Types : System.Nullable`1[System.DateTime]
Oct 2, 2009Im working on my first n-tier application. I am trying to serialize a structure and Im getting an error"Soap Serializer does not support serializing Generic Types : System.Nullable`1[System.DateTime]."Here is the structure that is being serialized
Namespace Structures
<Serializable()> _
Public Structure structAllergy
Public AllergyID As String
Public ProfileID As String
[code]....
The bold line is the line that is throwing the error.
DropdownList At Properties Level Of ComboBox - Search Field Types
Oct 28, 2009I have a combo box on my application (working with VB.net) called CmbAttendantstatus. I have sent the dropdownstyle = dropdownlist at the Properties level of the combobox.
There are 200 field types e.g;
Current Attendant
Ever Attendant
Never Attendant etc
The issue is I can only select one from the list, fine, but I want to be able to type the first letter on the combobox and it takes me to the nearest field type rather than looking through the entire drop list. For example I want Never Attendant, I just need to type N and the drop list takes me to anything starting from N and if I add E for example any field starting with NE shows up for selection. Presently, when the dropdownlist is selected you are not allowed to type anything...
Using Enums With INotifyPropertyChanged?
Mar 10, 2011I have a public property, "Status" that is an enum. I have a setter method that changes the status and raises the PropertyChanged event. However, the WinForms user interface is not properly updating. I'm pretty sure it's because Status is an enum. Although I was thinking enum was a reference type but I guess it's a value type. Does INotifyPropertyChanged work the same with reference and value types?
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INotifyPropertyChanged And Programmatic Changes To GUI Controls?
Jun 17, 2009Okay say we have a class that implements INotifyPropertyChanged and a property that has code in the setter to raise the PropertyChanged event. On the GUI side we have a text box with the code:
txtFirst.DataBindings.Add("Text", p, "FirstName", True) Where p is a Person object and FirstName is the property that raises the PropertyChanged event.
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.net - Get INotifyPropertyChanged On Multiple Inherited Objects?
Sep 2, 2011I have a class, Vehicle. I created two child classes, Car and Plane. I want to monitor the speed, which is a Vehicle Property, and bind it to a control (label, or image, for example) in WPF. When i create a static Class which only purpose is watching the Speed Property, it works, as far as the INotifyPropertyChanged is declared with the Speed Property name.
But the problem is, I have to create dynamicly multiple Cars and Planes by looking in an XML file and deserializing my objects, and creating multiple Car or Plane UserControl (Let's not discuss this way of working, please). So I have to get the Speed property inside the Vehicle Class (which is normal), and I have to get a INotifyPropertyChanged on each Speed of each Vehicle Created. So, my Cars and Planes are loaded, and I have to get all speeds, but I can't create a static Speed property by Vehicle. By the way, by creating a non-static Speed property (as int, for example) in Vehicle Class with INotifyPropertyChanged raised in the setter, it does not work. The event seems to be raised, but my converter is not fired, and my controls does not update.
In my Vehicle Class
Private SpeedValue As Integer
<XmlIgnore()>
Public Property Speed() As Short
Get
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The PlaneView Class is almost the same for this part.
I confirm that the converter is fired just once, the first time, when the tabs are created, because I put a breakpoint on the Convert function definition. After that, the converter is never fired again. So the picture img_fonctionnement is displayed, but it is never updated. But the Speed property is updated, I swear. And the INotifyPropertyChanged (in Speed's setter) is raised, as far as i know with the help of the debugger.
And the "an item with the same key has already been added" (which appears in a messageBox, and not as an exception) seems to appear only when I am to long with the debugger. In normal execution mode, it never shows.
C# :: Determining Object Equivalence For Value Types, Reference Types And ILists?
Nov 1, 2009I have a class with a Property called 'Value' which is of type Object.Value can be of any type, a structure, a class, an array, IList etc.My problem is with the setter and determining whether the value has changed or not.This is simple enough for value types, but reference types and lists present a problem.For a class, would you assume that the Equals method has been implemented correctly, or just assume that the value has changed every time the setter is called?If I did assume it's changed, then perhaps I should assume it for value types as well, so that the behaviour is consistent.
View 2 RepliesINotifyPropertyChanged.PropertyChanged Implemented And Not Implemented; Visual Studio Build Error
Jan 2, 2012I'm seeing a strange build bug a lot. Sometimes after typing some code we receive the following build error.
Class 'clsX' must implement 'Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs)' for interface System.ComponentModel.INotifyPropertyChanged'.
And
'PropertyChanged' cannot implement 'PropertyChanged' because there is no matching event on interface 'System.ComponentModel.INotifyPropertyChanged'.
Those error should never go together! Usually we can just ignore the exception and build the solution but often enough this bug stops our build. (this happens a lot using Edit and Continue which is annoying)Removing the PropertyChanged event and retyping the same code! sometimes fixes this.We're using a code generator that causes this error to surface but just editing some files manually triggers this exception too. This error occur's on multiple machines using various setups.
Pass A Nullable Valuetype Into A Non Nullable Valuetype?
Sep 17, 2009I accidently wrote some code today that was like this[code]...
I immediately noticed the issue, but I had already hit the run button. It compiled successfully, I ran it through to the section and it threw an exception.
You can't do this in C#, it gives a compile error "cannot convert from 'int?' to 'int'".
Is there an 'Option Explicit' type switch that I can turn on to ensure that this sort of error does not occur again?
Compare Two Types In Dictionary Of Types .net?
Jun 23, 2012I need to compare two dictionary values if the types stored are equal, this is what i have
if gettype(Args(key)) = gettype(argtypes(key)) then
'' do something
end if
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Make Custom Properties In Properties Window To Refresh Upon Change Via Code?
Apr 26, 2012[code]I want to make the Properties Window to update the properties for X and Y at each MouseMove, so they become immediately visible for the user.
View 2 RepliesUser Control Properties - Finalize My Design Time Properties Grid
Apr 27, 2011I'm making a control and I am trying to finalize my design time properties grid. I have several List(of Class) items as public properties and when I click on the design time menu (while testing the control) there is the word "Collection" and a button with an ellipsis (...) that brings up a neat pop up with the buttons Add/remove and all of the public properties of the collection's class on the right hand side. Basically for a non-collection instance of a class (with public properties) I'd like a similar button to show up. I know I could put all of the properties in the main control class and group them, but I like the pop up box feature. Anyway to duplicate this? (think font grid item etc.)
View 3 RepliesVS 2010 Express - PictureBox Design Properties Box Shows Properties That Cannot Be Accessed?
Mar 5, 2012In the form design I set up a TableLayoutPanel, 20x20 cells and in cell (1,1) a PictureBox (called Target) containing the image of a small target. The properties box for Target shows some very promising properties, Column and Row - and if you overwrite the values in the properties box, the PictureBox obligingly shifts to the corresponding cell position in th design. However in VB it is not possible to refer to Me.Target.Row or .Column - neither appears during coding in the menu of properties, and deliberately coding either of them produces an error like
Error 1 'row' is not a member of 'System.Windows.Forms.PictureBox'.
1. Why does the properties box show properties that cannot be altered programmatically?
2. How can my program move Target around in the TableLayoutPanel?