Invoke HasValue On A Nullable Property Of An Object Via Reflection?
Sep 15, 2010
This function loops all properties of an object to create the updatequery to save te object to the DB.
We had to make some changes to it because of the introduction of nullable properties. If the property is nullable we would like to check the 'HasValue' property. This does works when it has a value. When the property has no value we get an 'Non-static method requires a target'-error at the CBool-line
An other way to check the 'HasValue'-prop of a property using reflection?
Private Function GetUpdateQuery(ByVal obj As Object, ByRef params As List(Of SqlParameter), Optional ByVal excl As String() = Nothing) As String
Dim sql As String = String.Empty
I'm working against a SQL Server database that regularly has DateTime columns that can be null. I'm using LINQ to SQL to connect my WinForms (VB.NET) program to the data. I've extended some of the LINQ objects and added a couple of Nullable(Of DateTime) properties. Basically, I'm calculating whether a particular value exists. The value is a DateTime. If it doesn't exist, I want to create a Nullable(Of DateTime) object (structure, whatever) with the HasValue property set to False.
I searched on the forum / Internet for the solution how a PropetryInfo object (of a Public property) can reveal if it has a Private Protected Setter ... it was all in vain .... all help I found was about how to "Set" value of a public property having a Private Setter.I would like to know if I have a PropertyInfo object of a public property, how would I know if its Setter is Non Public?
I tried, in a exception handling block, where I did a GetValue of the PropertyInfo object and then called SetValue by setting the same value back... but to my surprise it worked well and didn error out.
How to get the object description using reflection. I can get the name, value, etc... but not the decription like in .net.For example the description for .Text is "Gets or sets the text associated with this control." I thought maybe using MethodInfo, but does not give the description.
Dim MethodObj As MethodInfo Console.WriteLine("Methods:") For Each MethodObj In GetType(TextBox).GetMethods() Debug.Print(MethodObj.Name & " " & MethodObj.ReturnType.ToString()) Next
I've created a MyFunc extension (in Module Extensions) for all the base types as well as generic arrays, ICollection(Of T) and Dictionary(Of String,T):
Function MyFunc(Of T)(a() As T) As String Function MyFunc(Of T)(collection As ICollection(Of T)) As String Function MyFunc(Of T)(dict As Dictionary(Of String,T)) As String
I'm trying to check if a variable has been defined as a nullable Guid. eg.
Dim myGuid As Nullable(Of Guid) or Dim myGuid As Guid?
It seems doing a myGuid.GetType returns the underlying type, that is type Guid, not Guid?. So testing myGuid.GetType Is GetType(Guid?) always returns False.How do I find out if myGuid is a nullable type?
Ed: I can do the following, which correctly returns True for "Guid?" and False for "Guid":
Not Nullable.GetUnderlyingType(GetType(Guid?)) Is Nothing
The problem is that I don't know how to retrieve the nullable type from the variable itself, in order to test it. I've only been able to get the underlying (non-nullable) system type.
I've written a db helper function. I pass it an object comprised of public members, representing the row data of a table. The members are the table columns.Using reflection, I loop through these public members to create an INSERT statement for a command object and populate its parameters with the values in those members. So far so good.But now there's a table which has a uniqueidentifier column which I must not populate from the row object, as it defaults to "NEWID()" (using SQL Server 2008). Instead of skipping all Guid columns, which would be easy, I only want to skip ones defined in the row data class as "Guid" (non-nullable).Basically, I'm using the Guid? (Nullable) type to indicate it's ok to populate that uniqueidentifier column with data. If it's non-nullable, that tells me to skip it because the column has a NEWID() default value.
I'm having problems with a program where I've got some multi threaded activities addressing the states of check boxes, which in turn are created by a user definable interface To achieve this I'm using the code below, which works on some occasions and crashes on other occasions when it stops with the following error NullReferenceException was unhandled Object reference not set to an instance of an object.Delegate Sub CBSetCallback(ByVal cb As CheckBox, ByVal value As Boolean)
Private Sub SetCheckBox(ByVal cb As CheckBox, ByVal state As Boolean) If cb.InvokeRequired Then Dim d As New CBSetCallback(AddressOf CBset) Invoke(d, New Object() {cb, state})
I am creating a setup project for my VB application. Everything seems to look fine. However when I tell it to build the solution I get the following error:Property 'keycode' is non-nullable. I have never seen this before in other setup projects and I can't find any help from MS.
In the below sample code, I have tried to use Nullable(of T) for DateTime and I want to use it same of the Dimensions property which is List(of Dimension).
I was under the impression that any time I set a Nullable(Of Something) to Nothing, it will take the value of Nothing.In a class, I have;
Private _something As Nullable(Of Double) Public Property Something() As Nullable(Of Double) Get Return _something End Get
[Code]...
In my page, using this class I set Something = Nothing, but as I step into the Set method, value = 0.0.Am I doing something wrong here? Or do I just not understand Nullable types yet?
I tried to build my project but it has 1 build error :Property 'Keycode' is non-nullable. I double click it but it points nowhere. I'm really desperate. My project consists of Crystal Report. It had just been upgraded from version 8.5 to version 11. Is it possible that this is the source of error?
How to get property.value from reflection.assembly?
Dim assembly As Assembly = assembly.GetExecutingAssembly() For Each assemblyType As Type In assembly.GetTypes() If assemblyType.IsSubclassOf(GetType(Form)) Then
[Code] Now the problem is that after i put this user-control in a form, I have to set a value for the Handled file. Otherwise it gives me a value cannot be null exception. Is there a way that i can set code that would execute in the case of the value being null? [Code]
I know its unlikely but I was wondering if there is any way to get the comments (i.e. the bits after the ''') of a class or property..? I have managed to get a list of properties of a class using the PropertyInfo class but I cant find a way to get the comments / description.. I need it for a guide I am writing for the administrators of my site - it would be great if it could automatically update if new properties are added, so there is no need to worry about updating it in the future too much.
I am retrieving several properties of a control. Here is how I used to retrieve properties (with pinfo of type PropertyInfo):
value = pinfo.GetValue(obj, nothing)
That worked well, but now I am facing a property that has a optional value, and I get an error message telling me that the number of parameters is incorrect. So I changed my code by this one:
Dim index As Object() = {Nothing} value = pinfo.GetValue(obj, index)
At this point, I didn't get any error message, but this code doesn't retrieve the good value. It only works if I replace Nothing by the default value provided by the property accessor...
But I don't know in advance what this default value is! And this code is within a function that retrieves properties that doesn't have optional values, so I cannot change the code especially for one case or another..
I am working on .NET 2.0
EDIT: More precisions about the case leading to the problem
Here is an example of property leading to the problem:
ReadOnly Property Foo(Optional ByVal Number As Integer = -1) As String Get If Number = -1 Then
[Code]....
With this kind of property, none of the codes above retrieve the good string.
My best guess would be to try the first code for general purposes, catch the appropriate exception, and then dynamically retrieve the default value of the parameter (Number in that case) and its type, so that I can call getValue with this default value.
So, How can I retrieve the default value of the optional parameter?
When I got a fieldsinfo-array of a class I know all of it's fields. Now, how can I access all of the fields of an instance of the same class by using the fieldsinfo-array? [code]I'm sure there exists a possiblity to get the value of the instance, but how?
Okay, none of the previous questions I have seen with this error seem to apply in this situation.tEmp is a class that contains (among other things) two nullable date fields.[code]During a routine on my form, I am attempting to see if the following conditions are true[code]I get the above error (the title of question), but when I hover over the debugger, NextReview and InsuranceEligibleDate are both Nothing (which is correct for the employee I am looking at).I am using VB2010, and the Properties in the Employee class are using the new way of declaring Properties (i.e. no set/get)
Is there a way for a property to access its own name and type at runtime using reflection? I want to access this info without hard coding the name or index of the property in the class.
Simple Example Code:
Private ReadOnly Property MyProperyName() As String Get Console.WriteLine((Get Current Property Info).Type.ToString) Console.WriteLine((Get Current Property Info).Name)
how to invoke methods, but how does one change a simple property?
For demonstration-sake, here's a very simple set of code that should help. Let's say I need to set the visible property from a child form, and thus, it needs to be invoked:
Friend Sub activateItem(ByVal myItem As PictureBox) If myItem.InvokeRequired = True Then ????
I have written a .Net 4.0 Winforms Numeric Editor control (which inherits from TextBox), and I have added a Value property that is a nullable decimal type, as follows:
Public Class NumericEditor Inherits TextBox Private _value As Decimal? = Nothing
[code]....
how to get around this exception, particularly when I'm databinding a number field to a number property, and there should be no string conversion happening. (To further complicate things, I'm using a similar technique for another control where I databind a DateTime field to a nullable DateTime property, and that control works just fine.)
I'm trying to assign a date object to nullable but my code error on CBDate1 = nullDate. The message indicates that I need to assign a value to a nullable. This is my first time using nullable[code\]...
I'm trying to assign a date object to nullable but my code error on CBDate1 = nullDate. The message indicates that I need to assign a value to a nullable. This is my first time using nullable.
