I have a databound ComboBox on my form. Is there any way that I can make the first field blank.
I can do this with a DropDownList in the HTML part of .Net but is there a way to do it for a ComboBox?
Im writing an app which connects to a SQL Server database, via datasources / datatable.When Im looking at my .xsd I can see DataTables containing DataColumns. Each DataColumn has a 'NullValue' property which defaults to '(Throw exception)'.Because I have nulls in my tables I have gone through the fields and set all System.String fields to NullValue = 'Empty', System.int32 field to NullValue = 0.
View 1 RepliesI am getting an error when i try to populate some combo boxes with a value, the combo box has values in and the right amount the code is getting the right number.
the error msg is "Object reference not set to an instance of an object."
I am building a data based application using VB 2008 an SQL Express. I need to create textboxes on my form using code, (With & End With) method. I need a simple code string that will allow the app to check if the field to wich the textbox wil be databound is Nul, If so the textbox will not be created.
View 8 RepliesHow to use a databound combo box to display one field in the drop down, and another as the combo box text on roll up? Using VS 2005... For example, I have a datatable that has 2 fields. One called "ShortDesc" and one called "LongDesc". I want to be able to see the "LongDesc" column values in the drop down on the combo box. When I make a selection, I want the text in the combo box to read the corresponding "ShortDesc" value.
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I need to set a field that i have dumped into a dictionary to a value that is always a string, (well, it came from an xmlElement, so the .value is a string)
Function setMembers(ByRef ClssObj As Object, ByRef nLinkObj as Object, ByRef xml As XElement) as integer
Dim fields As New Dictionary(Of String, FieldInfo)
[code].....
I using ADO to get som values from a SQL DB one off the fields can have the value NULL And if i use:
txtinfo.Text = RS(
"info").value
Then i get an error.I have try with IS NULL - but that dosn't work
how to delete row in a CSV file where there is a null value in a partcular column? I am using VB. There are three columns I am using Post Date, Account Number, and Credit Amount. I want to delete all rows with null values in the Account Number column. I am very new to VB, took one class. I am using the Microsoft.VisualBasic.FileIO.TextFieldParser?
View 1 RepliesI am using visual studio 2010. I have a text box bound to a sql datetime field.I have to be able to either set or clear the text box. I can set it to any date fine, but when I try to clear it I am unable to save the record.i am using the binding navigator to save.
View 5 RepliesHow do I set a null value for an optional DateTime parameter in a constructor?
I'm using the following constructor below and I want the optional parameter admissionDate to be a null DateTime. Setting it to Nothing actually gives it a value (something like #12:00:00 #).
Public Sub New(ByVal obj1 as Object, Optional ByVal admissionDate As DateTime = System.Data.SqlTypes.SqlDateTime.Null)
is there any trick (because I can't think of anything else ! ) to massively set all of the properties , of a user defined class , to their null values ? You see , I have a class called Apartment and it has a lot of properties (it only has properties , no methods or events , if that's important) and those properties are either strings , doubles or integers . I want each time I create a new instance of that class (a new apartment , that is) to automatically set those properties to their null values . That is all of the strings to be equal to "" and all of the numbers to be equal to 0 . Back in VB6 I could rely on VB6 to do this automatically , but now in VB .NET , whenever I create a new instance of a class , all the properties start with the value = Nothing . I know I can define every property in the class module like that : Public MyVariable As String = "" but I'd like to keep them as they are and set their null values directly whenever a new object of that class is created .
View 8 RepliesQuestion is: How to test for null value of a field in an ADO recordset.Using Visual Studio 2010 Ultimate - VB.NET
ADO Connection to ODBC database
I am working with a table that contains about 10,000 records of which I need to do additional processing on about 1500. The records I need to process are qualified by the field'Cataloged' = True. The problem I have is the table allows for True, False or Null values (I have no direct control of the table to change from allowing Null) for the field I need to test.I run into errors when the value of the field is Null and need to figure out how to determine its Null state prior to trying to qualify the field as True or False value to prevent the errors.
I have an ASP.NET application that crashes when a null date value is returned.
The code line is:
excelWorksheet.Cells("A" & xlRowCounter).Value = IIf(IsDBNull(dRow("sysdate")), "", Format(dRow("sysdate"), "MM/dd/yyyy"))
Error message:
ERROR: System.ArgumentException: Argument 'Expression' is not a valid value.
How would I check for a null date, and replace it with "" in my app ?
I'm trying to test a varbinary(max) field to see if it's null. I'm trying to figure out if it's a null or not in the select statement, hoping to avoid having to do this locally for every row of the returned dataset. This is the SQL I'm using,
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I use following codes to display image from sql server. [code]...
View 3 RepliesI have a field in a datatable (dt) that can be integer or NULL.
View 7 Repliesi have a maskedtextbox which will accept only date in the format of "DD-MM-yyyy" no i want to insert this date in my db. i have done this successfully.
Now i want to insert null value in through that maskedtextbox .
I am trying to do a SQL query to see if an Address already exists in my database. My addresses are structure like this:
line1
line2
line3
city
state
zipcode
country
Sometimes line2 and line3 are NULL values in my database.I am using .NET TableAdapter and DataTable to make my query. When I try to pass in my line2 parameter (@line2) it is equal to a string with value = nothing. My database does not interpret this as NULL and says the records don't match, but I know they do? How do I pass in a string = nothing and have it compare to a NULL value in the database as being equal? I have tried string = DBNULL.value but won't compile.I have done similar comparisons with integers etc. using integer = Nullable (of integer) but this does not exist for strings.
I have in my DB a few number fields, but I would like put null values or empty values in some of this fields...
I had try this but without results:
If valorcolocardebito = 0 Then
valorcolocardebito = Nothing
End If
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I have a datetimepicker and combobox on my form. If a user does not change the date on dtpicker or does not change text on combo box, these controls return null value, and the save operation fails. The controls are bound to data in a database.
View 1 RepliesI am calling a Java-script function, in that i am passing the value of hidden field, that hidden field i want to use at server-side, but the value of hidden field is null.[code]...
View 1 RepliesWhy when I try to save a null value from textbox at sql server 0 is saved?
View 2 RepliesI key-in data from textbox to datagridvie..........the date data the format datatable is:
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I've got a table that caches calculated values for certain dates. I want to use LINQ to select all rows where the calculated value fields are null.But when I use isNothing I get an error that LINQ can't translate this into T-SQL. Is there a way to select null values with link, like this...?
Dim var = From rec As Record In myDataContext.Records Where IsNothing(rec.calculatedValue) Select rec
Other posts on stackoverflow mostly discuss how to avoid or check for null values with LINQ.
Note: I can't just set cacluatedValue's default to -1 to flag records whose calculated value has not been set (and then select those records) because I run queries that sum/average the calculated values. Selecting nulls seems cleaner and less bug-prone.
I require the expression which determines if a Data Item in a DataRow is null.
Required Code
If MyDataSet.Tables("MyTable")Rows("MyRow").Item("CheckingItem") [IS NULL] Then
'[Do Something]
End If
Attempted Code Resulting in Thrown Exceptions
I have attempted the following code which resulted in the exceptions posted under them.
If CType(ds.Tables("MyTable").Rows(0).Item(2),System.String) = "" Then
Me.lblOutput.Text = "Good"
End If
System.InvalidCastException: Conversion from type 'DBNull' to type 'String' is not valid.
I am currently writing a program that needs the use of a database. At the moment I am trying to get a simple combobox working.The problem I am having is that I have never done any work with databases and VB08.I am using an access database that has the fields SMTP, Port, SSL
I want to populate a combo box with the field SMTP and from there I want 2 other labels to be filled in with the port and ssl details I was wondering a) How do I set the connection up with Visual Basic (within the database I am using MySQL to get the information) b) How do I go about populating the combo box?
I am writing a school project in VB2005 and am trying to hook up a second combo box that gets its information of what to display from the first combo box. My application is where a student takes a "test" but they can choose what instructor they want in the first combo box. From there, they choose from a test of what each instructor offers in the second combo box. As of right now, my first combo box works great and my second combo box has nothing in it. Just a note, when I debug, it shows my iUserID value as 0.
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I have a property called ReplacementTo and I set a value to it based on the selecteditem from the combobox, like this:
classEquipmentItem.ReplacementTo = cmbReplcmnt.SelectedItem.ToString
Now I can't use cmbReplcmnt.Text because what I actually need is the value of that SelectedItem
So problem is, if the user leaves the combobox as blank, it throws a null exception.I decided to use the IIf function then:classEquipmentItem.ReplacementTo = IIf(IsNothing(cmbReplcmnt.SelectedItem.ToString), classEquipmentItem.ReplacementTo = "", cmbReplcmnt.SelectedItem.ToString)
Unfortunately I still get the error I tried using a Try-Catch for it and it worked, but I don't want to rely on the Try-Catch, so I was wondering is there a another way to work this through?
I have an open database (dataset) with two tables. It is binded to toolboxes, but I have one field, what I have to calculate about other parameters. I have binding navigator, and I can set field values from controls (eg. toolbox). I can step my rows, with binding navigator. I can update my database. But how can I set field value from code?
I want a code line:
database.fields("fieldname") = something - or something like this
How do I set a field value in a VB.NET module using Reflection?
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