Im using VB in VS 2005.I have found several methods of testing if a value from a dataset is null. Are there differences between these two ways of doing it:
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Is one faster than the other? From some searching online, there seems to be debate about the best way to handle null values.
ok, I've finally got my test database issues sorted out, however now I need to actually modify my existing report to add the two new fields from my test database. I have made a copy of the report so that I am not modifying the original. I have deleted the two old fields and now want to add my two new fields in there. In the Field explorer window, I see an object called "dataset1" and when I expand it, it is using a view that includes fields from the table that I added my two new fields to.
The problem I see here is that I have gone in and modified the view to include these two new fields in my test database - but again, they are not showing up as selectable fields here. I am just assuming that "dataset1" is somehow pointing to the live database again and that I need to change the datasource location.In my solution explorer, I see an object called "dataset1.xsd" but the properties of that do not tell me much about where it is actually pointing to...
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I've got the following LINQ Statement:[code]invRecord.Pack_Num is a field of type Integer. This means that when I try to access it, if it is DBNull I get a StronglyTypedException. The above code throws this exception. If, however, I remove the "invRecord.Pack_Num = PSNum" and in its place put something like "True", the code works fine. So I guess my question is, why is that that invRecord.IsPack_NumNull() returns False when the value is in fact DBNull and what can I use as a conditional instead? I've been beating my head against the wall for a while now and I can't find a solution to this problem.
View 1 Replieshow to set a field in a dataset table back to <DBNULL>?
View 4 RepliesI've got the following LINQ Statement:
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invRecord.Pack_Num is a field of type Integer. This means that when I try to access it, if it is DBNull I get a StronglyTypedException. The above code throws this exception. If, however, I remove the "invRecord.Pack_Num = PSNum" and in its place put something like "True", the code works fine. So I guess my question is, why is that that invRecord.IsPack_NumNull() returns False when the value is in fact DBNull and what can I use as a conditional instead? I've been beating my head against the wall for a while now and I can't find a solution to this problem.
This is what I'm doing to select and display 3 columns of my datatable in GridView:
Dim myCustomers = From Cust In myDataset.Customers _
Select CustomerId = Cust.CustomerId, _
CustomerName = Cust.CustomerName, _
ExpiryDate = Cust.ExpiryDate
DataGridView1.DataSource = myCustomers.ToList
The expiry date has null values in many records whose expiry date is not set.On executing the query I get runtime error:System.Data.StrongTypingException "The value for column 'ExpiryDate' in table 'Customers' is DBNull."
Obviously, my LINQ query is wrong or incomplete, but I am not able to figure the way to do it correctly.
I am trying to work programmatically with a dataset. The tableAdapter was created by dragging and dropping the dataset on my form, and then deleting the binding navigator and dataviewgrid. The problem I am having is when I am trying to delete a record that is DBNull. The dataset.delete( ) call creates fields for each of the fields, along with their data type (say Description as String). but I get an error whenever the field has a DBNull value.
CourseTableAdapter.Delete(DBDataSet.Course.Item(1).CourseID, DBDataSet.Course.Item(1).CourseDescription)
The error is Throw New Global.System.Data.StrongTypingException("The value for column 'Description' in table 'Course' is DBNull."I do have Option Strict On, but the problem exists even if I turn it off.
I have the following query
Dim get_rmf_2 = From rmf In t_rmf _
Where rmf!NIVP = nivp_rap
When i run it i get an error :
Operator '=' is not defined for type 'DBNull' and string "test".
I suspect this is because the column "NIVP" in the datatable contains null values, I've tried yhe same thing without null values and it works.So how can i make this work ? ; the column "NIVP" really has a row "test" , and a normal SQL query works fine.
I don't understand the error, Argument not specified for parameter 'test' of 'Public Shared Function TestThis(test As String)'.
Partial Public Class Form1
Shared Sub ReceiveCallback(ByVal ar As IAsyncResult)
Form1.Invoke(TestThis, New Object(){"test"}) 'error
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In my ASP.Net Web-Application, I'm getting this error: Conversion from type 'DBNull' to type 'Boolean' is not valid.
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I have this code List<string> myList = new List<string>();
myList.AddRange(new MyClass1().Load());
myList.AddRange(new MyClass2().Load());
myList.AddRange(new MyClass3().Load());
myList.DoSomethingWithValues();
What's the best way of running an arbitrary number of Load() methods asynchronously and then ensuring DoSomethingWithValues() runs when all asynchronous threads have completed (of course without incrementing a variable every time a callback happens and waiting for == 3)
I'm trying con build a simple chat client/software (whole in on executable) wich start listen from the start on the port 5900 and when a client connect to that port the chat is established.
The problem is that only the client can chat to the server, the server cannot answer the client because the connection is working in one way.The i've tried to connect from "server" to the client when it establishes a connection but the system crash warning me that the port is already on use.
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What is the difference between these ways to delete a file.Is one of the methods better than the other?Are there other ways to delete a file (. Net 4)
System.IO.File.Delete(path
to file)
My.Computer.FileSystem.DeleteFile(path to file)
I'm new to VB and have over the last week or two been looking at the different ways to play audio (mp3's). Windows Media Player, Microsoft Multimedia Control, Bass.dll, SndPlaySound, MCI SendString and DirectX (including audiovideoplayback, direct3d and directsound.) I originally decided to use windows mediaplayer, mainly because it seemed the logical choice but quickly found out I couldn't get it to work properly.
So I installed the Directx SDK but now I'm completely overwhelmed about what to use and why. I need to be able run the compiled code on a win 2k box, play an mp3 from start to finish then load and play another mp3 from start to finish and so on. Whats the difference between the varied choices and which would be the best for me to use?
I want to know by how many different ways I can create an object. The most common usage I am aware about is:
Dim obj as ClassA = new ClassA().
I'm new to VB.NET programming.What I'm confused about is the different ways one can declare a variable.Would someone please explain the difference between the two declarations below? [code]
View 2 RepliesI'm new to VB and have over the last week or two been looking at the different ways to play audio (mp3's). Windows Media Player, Microsoft Multimedia Control, Bass.dll, SndPlaySound, MCI SendString and DirectX (including audiovideoplayback, direct3d and directsound.)I origninally decided to use windows mediaplayer, mainly because it seemed the logical choice but quickly found out i couldn't get it to work properly. So i installed the Directx SDK but now i'm completely overwhelmed about what to use and why.
View 3 RepliesWhat are the different ways to send the emails using vb.net?
View 4 RepliesI'm looking at creating an mp3 player to keep myself busy. However I'm trying everything I can to avoid using the windows media player COM component. It makes it a little too easyWhile looking around I stumbled upon the DirectX.AudioVideoPlayback namespace and I was wondering if this would be sufficient. Would I be able to create an equalizer and other more advanced things for my application?
View 2 RepliesJust found out the hardway that there is no longer support for Direcshow for VB.net and C#. Does anyone know other ways of playing mp3s in VB.net, or even video for that matter?
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and from VB6 project I reference to Test.dll but an error messege was appear A reference to Test.dll file could not be added (If I create VB NET project and reference to file Test.dll it OK )
I am trying to create a bunch of records, there will be a limited number of "Codes", about 50. Each "Code" is associated with a name from a textbox, I was trying to have it save each one when you click a button, to a .txt file.So, from the start the record will be blank, the person will go through the form, choose a number from a numerical up and down box, pick a name associated with it (both of these are mandatory and not implied). When they click the button, it will save the contents I talked about into a .txt file, say the number is #2, and the name is "Bob", the next time they try to change that value for #2, it will overwrite "Bob".
View 6 RepliesPresuming "instantiate" is the appropriate terminology, may I get some insight as to which of these are better, more efficient,[code]...
View 3 RepliesI'm using VS 2010 so I have auto-implemented properties.I have a class and I want to access the properties by a string.[code]But, I also want to be able to access the variables something like this way.[code]How can I setup MyClass to work both ways?
View 7 RepliesI want to store say like 8 values, that in the end will be combined into one string. What's the best way to store them? They should be reached in a own namespace I did. In a separate .vb file. I want to able to edit them. The values are both text and numbers. So whats the best way according to you?
View 3 RepliesI have come up with this 2 methods of reading all records on a database table. Both work nice but I would like your expert opinion on which delivers best performance and why.We are reading table "DATA" and filling an array called lstData with the contents of the "Data" field.
1) Method one is using the bindingsourse to go through all the records.
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My guess is that the first method, while simpler to the eye could use more overhead. What I really would like to know is if the second method really delivers better performance and if it is worth doing all the manual SQL queries.
This is a VB.Net newbie question. I'm confused at the different ways to declare and define variables.Here's an example:
Dim URL As String = http://www.c-sharpcorner.com/default.asp
Dim request As HttpWebRequest = WebRequest.Create(URL)
Dim response As HttpWebResponse = request.GetResponse()
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What ways do people know how to speed up vb browser??
View 1 RepliesI have a general question on app.config, or the best way to NOT hard code a SmtpServer.Host = XXXXXXXX setting. I wrote this very simple SMTP texting application and wanted to have the settings not hard code but a form that read or writes to app.config or .ini or registry. my question is the pros and cons? and if anyone hae suggested or a link to sample project that is doing what I'm after. I have a single .exe and am new to vb.net and either want the exe to check for app.config, ini or registry if does not exist to create and then save added config, if the exe runs again it uses the newly created settings.
View 5 RepliesI've been going through a VB book I had while in College, and was trying to figure out different ways of making programs work.One assignment was to create a multi-dimensional array to figure out wind chill factors. The only part I really can't get to work right is using 2 numericUpDown controls. Using 2 dropdown menus was obviously easy because the items are indexed, but as far as I know, numericUpDown controls are not indexed.
Instead I used 2 selectCase statements to determine the index in each updown control, then passed the indexes to a function to determine the answer.The numericUpDown controls both increment by 5, (wind from 5 to 30) (temp from -20 to 15)Just looking to see if someone has any ideas of a better way of doing this.
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