Straightforward question: I have a few variables that are doubles. I would like to be able to store a "null" state in them, i.e. I need to be able to represent that the variable doesn't contain valid data. I'd really rather not associate a boolean "is valid" variable with every single double
View 2 RepliesI'm working on a vb.net application which imports from an Excel spreadsheet.
If rdr.HasRows Then
Do While rdr.Read()
If rdr.GetValue(0).Equals(System.DBNull.Value) Then
[Code]....
But when passing the value to the SQL insert I get: "Nullable object must have a value."
Solution:
Fixed by changing the datatype of the parameter in the sub I was calling and then using Variable.HasValue to do the conditional DBNull insert.
I have a situation where I am handling both single & double mouse click events on a form. In both cases something has to be loaded, however when a double click occurs, I do not wish to execute the code attached to the single click event.Is there a way to intercept the mouse click's and check if double or single and then execute the right event appropriately?
View 2 RepliesI have a value $17.50 as a string..how would i convert it to a double 17.50?
View 2 Replieschange my MDIClient's background image I've decided that painting over it is the best way to go (because of scaling). Problem is, when the form (and the MDIClient) get scaled/resized, there's massive flicker even with the ControlStyles and form double buffering.
Public Class frmMain
Dim BGimage As Image
Sub New()
[code]....
I used advice from this site to set the DoubleBuffering property of a Panel to true.url...However, I don't see my new control in my toolbox. To get by I have drawn regular panels in my designer window and then altered the designer file to my new class. This causes headaches though when the designer doesn't open correctly (sometimes it works, other times I get a "variable is undeclared, unassigned error)..How do I get a simple custom control into my toolbox?
View 5 RepliesI've done arrays before but,
For x = 1 To 5
Dim canvas(x) As ShapeContainer
Dim cell(x) As RectangleShape
[code].....
im using this bit of code to recieve data from a database. problem is if one off the values in the databass is null it kicks up an error how can i handle this so in the event of a null value it gives a "" string value
[Code]...
I'm confused at the variety of different ways to say "null" in VB.net. I've got text and numerical fields with checkboxes to mark unknown values; I just want to populate a table with the fields' values (if the corresponding checkbox is not checked) or null values (if checked) so I can later input them into a mySQL database.So my question is just which of the various null types I should be using in what situations.
View 6 RepliesI want to select all records in a table and only 1 field in 2 related tables so my query is:
strSQL = "SELECT CL.Name, CL.FirstName, T1.Description, T2.Description " & _
" FROM Clients CL, Table1 T1, Table2 T2 " & _
" WHERE CL.Tab1Cod = T1.Code " & _
" AND CL.Tab2Cod = T2.Code"
All works and all records are selected only if fields CL.Tab1Cod and CL.Tab2Cod contain data but if one or both contain NULL value then NO record are selected. how can I test in a query statement if a filed contains a null value and, in this case do not expose the related field ?For example if CL.Tab2Cod is null the field T2.Description will be empty but all other fields are exposed.
I have a htpc project that I am working on. The main program loads dll plugins which are basically other win forms. On each of these forms, including the main program, I use a picturebox (a double buffered picturebox) for the background image and then draw everything on it by hand. Whenever I load the form from the dll and show it, I get a weird flicker. It looks like it is the previously used double buffer. Is there any way to clear the background double buffer before the flicker? Or am I going in the wrong direction?
Here's a couple of videos of the problem:
[url]
[url]
Notice the black screen with the white lines on it or the flash of the desktop after I click "Movies." How do I get rid of that?
I have written this code and tried running it but I am getting errors in the code segments below. The error says "conversion from string to double is invalid". whereas the calculation for 'y' is an addition so should not be giving the value it is giving at the moment. ICCPtotcircuitres is also returning 'nothing'.
Private Function iccptotcircuitres(ByVal x As String, ByVal y As String, ByVal z As String) As String
Dim Res As String
Res = x + y + z
iccptotcircuitres = Res
[code]....
I was wondering if it someone could help me solve this problem. I have a full screen application with a panel in the center which is used to display different user controls and screens when the user uses the app.However, I have a rather large gradient image set as my form's background and it causes the panel to flicker every time controls are added. I find that when the background image is removed the flicker goes away. How can I keep the background image but eliminate the flicker? My form is already double buffered.
View 5 RepliesWhen I try to do:
Quote:
RichTextBox1.Text = Form2.WebBrowser1.Document.Body.InnerText()
RichTextBox2.Text = Form2.WebBrowser1.Document.Body.InnerText()
It says
Quote:
NullReferenceException was unhandled. Object reference not set to an instance of an object.
What's up with that?
I am creating a math related class and one of the problems I have been having was how to create a function to return the fractional part of a double as an integer. I could easily do that if there was a way I could get the length of the digits.
-3.141 should return 3
-0.125 should return 3
-0.5 should return 1
-0.4545 should return 4
I would like to do this without using string manipulation. So far all I have gotten on the web is unanswered questions. I thought of using log, but it doesn't give the desired result when working with numbers < 0
For greater accuracy I should use a Decimal instead of a Double ( so I've been told ). Why then have Microsoft chosen to use DOUBLE for most of the functions that return a floating point value in the Math Class?
[Code]....
I am trying to pull data from a cell in the currently selected row in a DataGridView control. I fill the control with data from a SQL database through a dataset.I am trying to retrieve the index of the currently selected row so that I can pull the data out of the first cell in that row. Here is the code I currently have:
Dim i As Integer i = dgvSchedule.CurrentRow.Index MsgBox(dgvSchedule.Item(0, i).Value)Seems pretty simple to me, but for some reason I am receiving a "NullReferenceException, Object reference not set to an instance of an object" error on the second line.
I just made a bunch of changes to my program, so I can't just undo what I did. My main form gives me the following error every time I try to load the designer:
Warning1Value cannot be null.
Parameter name: objectType
I have rebuild the project with no success. A few other posts have mentioned that there could possibly be a reference to a button or image that no longer exists, but I have no idea which one.
Also, I don't really know what the information below means, but it shows up on the error page under 'call stack', so I figured I would include it
at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.GetRuntimeType(Type objectType)
at System.ComponentModel.TypeDescriptionProvider.GetRuntimeType(Type reflectionType)
[Code].....
I'm having trouble figuring out what to do with the bolded part, when there are no nodes to return.If there are no image tags inside the <images> tag, i get an "Object reference is not set to an instance of an object".I have been searching and searching for an answer but can't find one.
Dim orders = From o In xmlLinq.Descendants("order")
Select New With { _
.orderID = o.Attribute("id").Value, _
[code].....
This is related to my last question.Even though Access considers Nulls and zero-length strings (ZLS) separate values, often developers wish to treat them as equivalent for the sake of an If...Then statement or some other stretch of code. One way to accomplish this is to write code like this:
' Not so efficient
If IsNull(varAge) or varAge = "" Then
' do something
[code].....
i keep getting this null reference exception error and i can't figure out what i need to do to fix it. I have this in the form
[Code]...
keep getting this null reference exception error and i can't figure out what i need to do to fix it.I have this in the form
Private Sub cbLookUp_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cbLookUp.Click
Dim webDownload As New Net.WebClient
[code].....
I've got a DataGridView that has a column that will show dates/times this column needs to be sortable so I use this to tell the DGV that it is storing Date type objects (so that sorting works fine automatically):[code]Now the problem is that there will be some records shown in this DGV that do not have a value for this date column. How can I display this? If I dont set a value for that column or I set it to Nothing then the cell just shows the minimum date value (01/01/1601).Oh and this DGV is not using data binding if that makes any difference. Perhaps this might be a good time for me to investigate this data binding lark though if that will help with this issue? I'm sure I recall seeing something about being able to use one value but display another value when you use data binding thats all.
View 6 RepliesIn vb.net, im using objWriter.Write("playerA= "x"")as you can see im using double quotes inside double quotes, how do i skip it so the error doesnt show up?in php you make an "" to skip the string like ("playerA = "x" ")
View 6 RepliesI am currently in programming class and I have tried time and time again to complete a form called "theater revenue" that was assigned to me. Even though I have typed in a lot of code, it keeps telling me "Conversion from string "" to type 'Double' is not valid."
These are the directions: "A movie theater only keeps a percentage of the revenue earned from tiecket sales. The remainder goes to the movie company. Create an application that calculates and displays the following figures for one nights box office business at a theater. Assume the theater keeps 20% of its box office receipts. Use a named constant in your code to represent percentage."
Here is my code....
vb.net
Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
' Declare variables for the calculations.
Dim dblATS1 As Double
' Gross Adult Ticket Sales as Double
[Code] ......
with this code I have cascading comboboxes that pull push results in a DataGridView; but each time I change selection in a combobox, it doubles results in the cascading combobox?!
Imports System.Data
Imports System.Data.OleDb
Imports System.Windows.Forms
[code]....
I'm working with an API, for this I'm using this particular call: [URL]
If i use this, I will get all the .price values:
For i = 0 To .bets.Length - 1
With .bets(i)
Print(.price)
End With
Next
Can I calc the average .price value? I will need to sum all the values as well.
[code]I'm trying to leave the textboxes A, B and C EMPTY so an error message box will appear saying "You did not put any value in textboxes A" or "B" "C".. but my program works if you put a value in the three boxes.[code]
View 6 RepliesI have a form, which holds several comboboxes, textboxes, checkboxes.I use an msaccess database to store the values into.When I enter text in a textbox and then click the save button I get the following error:conversion from string "" to type 'double' is not valid.But I really don't understand, the field of the database where the textbox text is being stored in is a text type.I searched google for it and the problem seems to be that the type of data from the textbox isn't the same as entered into the field of the database.But the strange thing is, is that as far as I can see, it is.[code]
View 5 RepliesI have the following code that checks if the value in a cell contains a nummeric value.
Private Sub dgvOrderRegel_CellValidating(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellValidatingEventArgs) Handles dgvOrderRegel.CellValidating
Select Case e.ColumnIndex
Case 4 'Aantal
If Not IsNumeric(e.FormattedValue) Then
[Code]...