Is there a way to change when an expression in a datacolumn is evaluated?
I'm trying to make a simple total function which sums the values of a particular column in a data grid. Normally the expression is evaluated when I leave from the datagridview, but I wish it to be evaluated when the row is changed.
I am trying to write following expression on a datacolumn. But it results in error:Replicate('*', nLevel) + NameWhere: Replicate() is a user defined function (in a module). nLevel and Name are two other columns in same data table.
View 3 RepliesIn the following
For Each <reference> IN <expression>is <expression> evaluated for each iteration of the loop? Specifically, if <expression> is costly to evaluate, would it be wise to evaluate it once before the For Each statement and keep the result in a local variable to use in the For Each statement?
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)
[Code]....
warinng message :- Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.
syntax: lblMessage.ForeColor = Me.f_Color.FromArgb(ds.Tables("Events").Rows(MNo).Item("Color"))
I use .Net 2.0 on this one and i have a warning , i noticed that it runs over a line , here's the code:
Dim i = 0, y = 10
For i = 1 To 5
y = y + 100
Dim pic2 As New PictureBox
[code]....
'Warning 1 Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.
i read an article about datacolumn.expression property here [URL]. this is really great. but i was just wondering, for my case i want to use my custom function to use in the expression. basically, on my datatable i added an unbound column AGE. when i display records, i just want the age textbox to be populated with the computation of the person's age based on birthdate.
View 7 RepliesI have a class with a static list of keys, and I have a static method called Remove() that removes a key from that list.Now what I understand from the contracts post conditions is that as the programmer of the class, I guarantee that the current public method does something specific, in this case : removing the element of the list.
Here's what I've written:
private static List<Keys> m_usedKeys; // private list of keys
public static void Remove(Keys _key)
{
[code]....
What I'm trying to "Ensure" here, is that the Remove() method removes the key for real from the list (Yes this might be a trivial example, but I get the error there.)when I write the Contract.Ensures() line, VS2010 gives me the following error :
Error 3 Detected expression statement evaluated for potential side-effect in contracts of method 'LibJungleTimer.KeyBind.Remove(System.Windows.Forms.Keys)'. (Did you mean to put the expression into a Requires, Ensures, or Invariant call?) C:UsersJoelDocumentsProgrammationJTJungleTimerLibJungleTimerKeyBind.cs 51
I think this error says that the expression m_usedKeys.remove(_key); has a potential side-effect. In fact, it has a side-effect, it removes a key from the list!If I try to write something like this instead :
Contract.Assert(!m_usedKeys.Any(x => x == _key));
well it compiles fine.
datacolumn expression subtracting dates and taking to datagridview
View 1 RepliesI am trying to build a filter string for my DataView, but I have run into a problem. My underlying DataTable contains values that are formatted when displayed in my DataGridView.For example, if the DataColumn contains 1.52 and the DataGridViewColumn.DefaultCellStyle.Format = "n0" then 2 is displayed.So the user sees 2, then sets the DataView.RowFilter = "DataColumn = 2", and no DataRows are returned. Is there a way to format the DataColumn in the RowFilter string? For example, DataView.RowFilter = "FORMAT(DataColumn, "n0") IN (2, 4)". This filter string should return 3 rows. If not, can LINQ do this?
View 5 RepliesI have a DataTable with two DateTime columns: "start_time" and "end_time".Now, I want to add a third column that calculates the difference between the two DateTimes. But I can't seem to figure out how. I've tried to set the .Expression-value to "start_time - end_time", but it says that "-"-operator is not allowed on DateTime.
View 4 Repliesi 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
I have added a column to a Datatable called CallsPerDay which is there to tell me how many telephone calls have been made on a particular day or days.Is there a datacolumn.expression which will allow me to Filter on the day, count the rows and then populate this added column with the result.
View 1 Replieshow do I overcome it? I have created a class and compiled into .dll This code
[Code]...
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]....
I want to change my filter expression if a certain item is selected in a dropdownlist and the person clicks the button
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
If DropDownList1.SelectedItem.Text = "JOANNEP" Or DropDownList1.SelectedItem.Text = "ANAB" Then
[Code]....
i tryed that however my gridview still shows byyyy years that include 2009
I am trying to get the version number out of the AssemblyInfo.vb file and replace it with a number that I choose.
Dim text as string = string.empty
Using sr As New StreamReader("C:fooAssemblyInfo.vb")
text = sr.ReadToEnd()
[Code].....
I thought it would be fun if I could write vb.net or c# code at runtime and the interpreter would automatically parse it like python does it, so I made a little program, which would do something similar. Basically it looks like this:
InputArgs = Console.ReadLine()
ParseInput(InputArgs.Split(" "))
Private Sub ParseInput(Args as List(Of String), Optional TempArgs as List(Of String))
[Code].....
I know it's not a good system, but it show's the basics. So my question is: Is it possible to make vb.net or c# like python - interpreted at runtime?
Quick question, of which the quickest and easiest answer may well be to rearrange related code, but let's see...So I have an If statement (a piece of code which is a part of a full working solution written in C#) rewritten using VB.NET. I am aware the VB.NET IIf(a, b, c) method evaluates both b and a regardless of the trueness of the first evaluation, but this seems to be the case in my standard construct, too:
If (example Is Nothing Or example.Item IsNot compare.Item) Then
'Proceed
End If
[code].....
How can I get the variable My.Application.Info.Version.ToString to populate in the comments section?[code]..
View 2 RepliesI have a DataTable that I am creating and binding to a GridView. Currently the headers do not have any spaces and it makes it hard to read. I want to space them out but I'm having a minor issue.[code]I know that I can set the HeaderText in the columns declaration like below, but I won't know how any columns I am going to have. And would rather the columns be generated automatically. [code]
View 2 RepliesHow do I go about adding a ButtonColumn to a DataTable.
I am basically using a DataTable as the DataSource of a DataGrid and need to add a ButtonColumn to the DataTable so that when I DataBind it to the DataGrid it all works.
Although when I try
dt.Columns.Add(buttonColumn)
This is not allowed. It has to be a basic DataColumn.
Anyone have any ideas what would prevent my data from not be ing able to be bound to my data column? [code]My error says cant bind to column named SellingPrice? I have many other columns ALL binding the same way and other parts of my program recognize SellingPrice ?
View 9 Repliesin my datatable I've a String.Byte[] column which contains the array of bytes of an image. So, when the datatable is binded to the datagrid, I can see the picture, if present, and the red cross if is not presente. So I can remove the red cross, by assign a value to the DefaultValue property of the datacolumn. But what default value I've to assign?? I tried with system.dbnull.value but the red cross is still present.
View 8 RepliesFirst of all - It`s my first post here so welcome I have a short question.I have an array with strings values, and a datacolumn with values of the same data type. The question is - what is the most efficient method to find values which are in the array, but aren`t in the datacolumn?
View 18 RepliesThis is the code I have:
Sub Main()
Dim dts As New DataSet
Dim da As New SqlDataAdapter
Dim SolTabla As New DataTable
[code]....
For example, I want to access the second cell value in "Columna". How can I do this with no using a Datagrid?
I have a dataset with a number of data columns, due to sizing issues I've updated a number of the varchar columns from say VARCHAR(20) to VARCHAR(50).I'd like the DataTable to automatically grab the new column information, is this possible? I'd rather not go through each column in the table and update the length.
View 1 RepliesPrevent an empty column in Excel to be loaded into a dataset column?
View 3 Replieshow to prevent an empty column in Excel to be loaded into a dataset column?
View 10 RepliesI defined a DateTime datacolumn in a datatable dt as [code]]....
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