New Member With MS Access Background?
Aug 2, 2009
I'm a newbie to this forum and want to make sure I don't muck things up and irritate everyone as tends to occasionally happen in some forums.I have a very solid background in MS Access (I use it as a front end to an Oracle database and use DAO methods to create native Oracle statements via pass through queries). I am going through the tutorial on VB 2008 Express download the MS site. I have a number of questions that generally have to do with "I did this with VBA in Access, how do I do the same here?"
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Jun 2, 2011
how do I overcome it? I have created a class and compiled into .dll This code
[Code]...
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Aug 13, 2009
In Visual Studio 2008, if I do this:
[Code]....
Does anyone here know how to get the above to work WITHOUT warnings being generated?
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May 31, 2010
In the following code i get a warning at line 59:Warning 1: Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.and.. At line 78 I get this Warning:
Warning 2 Property 'SelectedCustomer' doesn't return a value on all code paths. A null reference exception could occur at run time when the result is used.
The program compiles and runs well, but i cant' undesrtand the reason for these warnings. Any Idea ?
1: Public Class Form1
2:
3: 'Form level members
4: Private objCustomers As New ArrayList
[code]....
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Apr 28, 2011
Cannot appear to be able to get this function to not have the above error.Private Function GetIncidentActions(ByVal FromAgentID As Integer, ByVal ToAgentID As Integer, ByVal incidentAction As Integer, ByVal ActionDate As Date) As String
[Code]...
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Jun 23, 2009
i changed a class variable to shared so i can access it in all instances of the class, but it caused an error. what is causing this, and how can i fix it?
Private
Shared img As Bitmap
Me
.img = bgImage
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Apr 13, 2011
I've encountered a problem which challenges my understanding of access modifiers in VB.Net. I have a class declared Friend. If I declare its properties Public, the application works. If I declare them Friend, the application fails.
Before this, I believed that, in a class declared Friend, it would make no functional difference whether I declared the members Public or Friend. I thought class access declarations applied their restrictions to all nested entities, so nested properties declared Public were effectively restricted as if they had been declared Friend. Obviously, I was wrong. Can anyone explain how access modifiers really work, or point me to the relevant documentation?
Here is a more detailed description of the situation: I have a Friend class called StripTask with properties called StripDate, HistorianDate, and TaskText. I have a collection of StripTasks (called _StripTasks) which is used as the data source for a Syncfusion GridDataBoundGrid. The way the binding works, I need to pass the name of a StripTask property to each of the grid columns so each column knows what data to display. It ends up looking something like this:_DataBoundGrid.GridBoundColumns(1).MappingName = "StripDate". When the mapped properties are declared Public, it works. When the mapped properties are declared Friend, the grid is populated with the correct number of rows, but every cell is empty.
As a follow-up question, is it a good idea to avoid things, such as this Syncfusion binding method, which require me to pass property names as strings? It just feels as if I'm inviting trouble.
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Nov 29, 2010
I have a combobox that is bound to a BindingSource that contains a custom object with multiple Properties.
Is there a way to access a Datamember that is not displayed in the combo box and display it elsewhere. For example, When a user selects a name from the combo box, texboxes (or Labels) populate with Title, PHone, email, etc. All of this data is loaded in the custom object that is bound to the datasource so the info has already been pulled from the db and is in memory.
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Aug 2, 2011
I've used .NET for a long time but I've never really been sure of this warning :-"Access of a shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated"Whilst this is not causing an issue and I've not really experienced this problem a lot with my own code, converting some code from an old .NET project gives 10's of these errors.
Code:
Protected Function GetContentTypeFromString(ByVal TypeString As String) As MailContentType
Select Case TypeString.ToLower
[code]....
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Nov 6, 2009
After I formatted my laptop and reinstalled Visual Studio 2005, I receive a lot of same error as below message.
"Access of shared member through an instance; qualifying expression will not be evaluated"
If I click the error, it direct me to the line and all 102 error suggest me to add "Windows.Forms." before "DialogResult.OK". Should I add something on "Reference"?
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Nov 29, 2011
I'm wondering if this is possible. In my Test function below I want to
Check if T is of type BaseClass; throw an error if it's not.
Get the value of SomeText property of BaseClass.
Class BaseClass
[code].....
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Jul 26, 2010
I recall being told by a professor the following is bad practice. But it makes stepping through code a lot less tedious. I'm just solicting comments on pros and cons:
Friend Class MyClass
Private isEmpty As Boolean
Public Property IsEmpty() As Boolean
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Jun 9, 2012
I have a custom class called "Time" with the following function, for determining if one Time equals another Time.
Public Shared Shadows Function Equals(ByVal Time1 As Time, ByVal Time2 As Time) As Boolean
Dim x(2) As Integer
x(0) = CInt(Time1.Hour)
x(1) = CInt(Time1.Minute)
[code].....
Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.I know it shouldn't do any harm, just let the compiler skip evaluation, but is it a way of getting rid of this warning?
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Dec 4, 2009
Doesn't anyone use the dictionary member access expression? (a.k.a. the bang operator) If so, in what scenarios? url...
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Oct 5, 2011
I created an enumeration in a class library... and compiled it into a dll
Public Enum TestEnum
x = 0
End Enum
I then imported this reference to a windows form project as a referenced dll Public Class Form1 Dim mytestenum As TestPublicEnum.TestEnum Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
[Code]...
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Aug 4, 2010
I'm a newbie to threading, trying to learn it as I go. don't make any assumptions and try to explain threading concepts and rules that might seem obvious. I have a Module (Static class) as follows:
Module Main
Private ReadOnly _dbConn As SqlClient.SqlConnection
Public ReadOnly Property DBConn() As SqlClient.SqlConnection
Get
Debug.Print("Accessing DBConn")
[Code]...
All throughout the application, when i access DBConn on the same thread, it works as expected. howeve, later on I created a background worker that tries to access DBConn and nothing happens, the thread just hanges (the Background worker). I dont get the printout and the application doesnt continue. the background worker thread doesnt continue past that point, and so the thread never exits. I dont get any exceptions, and i Cant debug in Visual Studio (visual studio hangs).I guess its a 2 part question: why cant i access DBConn from the other thread, and why does it hang without giving me a threadAccess exception? also, why does visual studio hang (I'm assuming it hanges because the thread is hanging)?
Please Note: I am not asking about practice. I know I shouldnt be sharing the same connection, rather returning a new connection. in this particular application it is safe since (although i execute it on a background thread) as per the flow of the application, the connection can only be accessed one at a time. I just want to know why it hangs accross the thread.
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Jun 22, 2010
re: Access of shared member constant member enum member or nested type through an instance qualifying expression may not be evaluated I understand that this warning means that you should not reference a shared member via an instance. However, in my test case Test2.t.x("3"), I don't understand why it thinks I'm using an instance, since t is also a shared member. Also, note Test3. See what happens when you change declaration of GetObject() As Object to As Test3. I think I understand the behavior (not eval'd until runtime)
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Mar 3, 2011
Here's an example of what I'm talking about...
Public Class Sample1
Public Shared Function MyValue() As Integer
Return 0
End Function
Public Sub Code()
[Code]...
Me.MyValue gives a warning in VB.NET and (the equivalent code gives) an error in C#. Is there a particular reason for this? I find it more intuitive/natural to access the shared function using 'Me.MyValue' - but I avoid it to keep my warnings at 0. Did someone else just decide 'Nah, it makes more sense to do it the other way' or is there some technical reason I don't understand?
EDIT: I was thinking of it wrong, more like a 'sub class' in OOP. Even if something is declared in the base class, you access it through the instance you have. But that relationship is not the same with shared or static.
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Nov 18, 2009
I'm "cloning" objects in my code. For instance: objClone = objOriginal My question is: Does the assignment operator in VB.NET 1.1 do a member-by-member copy of the objOriginal to objClone or does objClone simply point as a reference to memory referenced by objOriginal?
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Oct 4, 2010
I have an application that I need to load data in a background thread and make available to a combobox or list box on my main form or UI Thread. I am really new to threading in VB and how to best accomplish this. Here is some code from a test project:
[Code]...
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Jan 6, 2011
I have 2 tables Table A & Table B Table A has the table values that I want to be populated in a datagridview control.The challenge is that column 1 in table A contains an ID(foreign key) to a name field that is a located in table B. I need the datagrid to have the first column be a combobox that displays the names(from Table B) that are already in table A via the ID's, but reference the populating values from Table B. So that when you bring down the combobox you would be choosing from Table B data but populating table A with the ID and you would see a name there instead of an ID.[code] How do I populate my DS dataset with Table B? And how can I create a link to these two tables using a bound datagridview control?
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Feb 24, 2009
I can't seem to find a good tutorial on how to access uithread components from the background thread.. It seems like there is different means of accomplishing this. I'm not picky about which one I use.
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Jul 27, 2009
I want to access a 3rd Party application in the background with the SendMessage method. It just needs to send a "space" to the software to trigger an action. It is important that this is done in the background because its a periodic event (ca. every 10 seconds), and it should be possible to simultaneously work on the same machine.
I tried to use the same approach which is shown in [URL]
The code I used is as follows:
Const WM_CHAR = &H102
Const BM_CLICK As Long = &HF5&
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd
[Code].....
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Dec 31, 2011
I have a drop downList and I have it listing colors. When a color is selected I want to change the background color of the page itself.
I am using Visual Studio 2008 and using VB.Net.
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Mar 23, 2012
I created a background thread that get's data and returns it to the main thread; this works. Now I want to be able to stop the SQL request from the main thread (probably on a button click). This is my test code for creating the thread (working):
[Code]....
How can I access the background thread to stop the query on demand? Do I need to set a flag on the main thread telling the background thread to stop running then have the background thread poll the main thread at intervals? I was trying to look for an example but I wasn't able to find a good one.
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Dec 16, 2011
I'm creating an executable that will run as a background service.I want to communicate with this executable with a browser - similar to how you talk to sophisticated copiers in a big office.and was told to build an HTTP interface in that app.All the examples of httprequest and httpresponse I can find are about talking to web sites - or public services.How would I go about having my app "fire an event" when an async POST is made from a browser page? How do I wait on a port in the app?
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Jan 3, 2011
I get this error if I follow these steps: Change property Y of an object (an associated entity property)
Attempt to submit changes At this point the value of Y and the value of X (the underlying key) are not in agreement -- LINQ to SQL apparently doesn't synchronize these until GetChangeSet is called.An expected error occurs due to some business logic or database level constraint during the update operation.At this point the value of Y is in agreement with X because GetChangeSet was called.Change the value of Y to Nothing (aka null).Call GetChangeSet.
The error occurs on the last step because the value of X and the original value of X (returned by GetOriginalEntityState) are different, and the new value does not agree with Y? Is that why? Is this a bug in LINQ to SQL. Must be because I don't see the same behavior if I change Y to another (non-null) value instead during step 5. What's the right way around this? I can see a few ways:
Discard the DataContext when an error occurs and leave the UI as-is. I don't like this because then optimistic cocurrency change conflicts cannot be detected. The new context doesn't have the original values in it that were populated at the same time the UI was populated, so if the UI has any stale values in it, they will cause data in the database to revert.Refresh the datacontext (OverwriteCurrent) and leave the UI as-is. I don't like this for the same reason as #1.Refresh the datacontext (OverwriteCurrent) and re-populate the UI. I don't like this because then the error message just presented to the user does not show the user the error they made and allow them to correct it. It also discards all the other changes the user may have made.When the error occurs, explicitly retrieve the key for Y that corresponds to the original value of X and reset Y, then call GetChangeSet to re-synchronize X (X is read-only or private so I can't reset it directly). This seems to work, but seems like a hack, and may require lots of code for other similar errors.
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Aug 31, 2011
I know I have done this before and as I remember it should be really easy. But for some strange reason I can't do it now and I am about to jump off the building.I will make it simple:Two tables, one is just a list of products and their code.The other table: "details" has a field named product. I want to store only the code there.In the second table's entry form, I am putting a combobox. This combo box should display the list of products, their names, but depending on which one is selected, the code is what is passed to the table "details". Currently If I set the display member to product and the value member to code it still pases the product to the binded data source.
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Dec 6, 2010
I have a database that holds information about a particular job. One of those things is a customerID. CustomerID links to another table containing customer details. I have a combo box attached to a custom object that holds customerID as the valuemember and CustomerName as the displaymember.The JobDetails holds the customerID info. How do I set the default selection in the combobox based on the ValueMember of the combo box?
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Oct 18, 2011
I have a small problem that I am sure is due mostly to my inexperience with threading. I have used simple entirely self-contained threads before, but not to a great extent. I understand the basic laws that surround them, such as how a thread cannot access another thread's member directly, and must use delegates.
[Code]...
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