So I'm working on this VB to C# web application migration and came across an issue that I'm hoping there is an easy work around for. There's a webform that uses the GridView control. In code, it passes the columns collection into a method that adds columns dynamically based on the user, permissions, and environment. So, the columns were passed into the function in VB using ByRef like so:
Public Sub PopulateColumns(ByRef ColumnCollection As DataControlFieldCollection)
'Do something
End Sub
Now in C#, I've used the ref keyword, but the columns collection doesn't have a setter. What's my quickest workaround for this? I'm going to be converting this over to a jQuery grid soon so I'm not concerned with best practices, but rather just getting it to work.
Here it is in C#:
public void PopulateColumns(ref DataControlFieldCollection columnCollection)
{
// Something here
}
which is called like this...
.PopulateColumns(ref EmployeeGridView.Columns)
The collection is already ByRef, so you do not need the ref argument.
So, unless I'm having a blonde moment, you just have to do:
public void PopulateColumns(DataControlFieldCollection columnCollection)
{
// Something here
}
.PopulateColumns(EmployeeGridView.Columns)
Tested and working.
Related
I usually make user controls containing forms for adding and editing data for a particular table in my database. I then show or hide these controls as the user clicks "edit" buttons, etc. It's common practice (for me) to put properties in the code-behind, that are used for setting the ID of the item being edited, into a hidden label on the page, and of course leaving it blank for new items being inserted. I usually only use C#, however, this time around I have to use VB.NET.
So in C# I would do the following:
public static int EditID
{
get
{
return Convert.ToInt32(lblEditID.Text);
}
set
{
lblEditID.Text = value;
}
}
..and then when the user, say, clicks an "edit" link from a gridview, I would
//set the ID of the corresponding record, something like this:
MyUserControl.EditID = MyGridView.SelectedDataKey[0];
Cool. So now I need to do this in VB.NET, and here's my code:
Public Shared Property EditID As Integer
Get
Return Convert.ToInt32(lblEditID.Text)
End Get
Set(value As Integer)
lblEditID.Text = value
End Set
End Property
but I get a syntax error that says: "Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.", highlighting the lblEditID for both the getter and setter.
I can't find any other SO questions about this, and I have Google'd just about every permutation of keywords I can think of, so this must be something really stupid.
What am I doing wrong here?
EDIT: Yes I realize I could just use a Session variable instead of the label, but I would still like to know why this doesn't work and how I could make it work with a label.
You don't want a Shared property for this. lblEditID is a label that exists in an instance of a WebForm class:- it can't exist until an instance of this class has been created, hence the error.
I don't really understand how the C# worked as this should be the same but I'm not a C# expert.
If you remove the Shared keyword it will work as you want I believe
I'm looking to populate an object then display the data to labels.
I've created a Student Class:
Public Class student
Public Dim sNum As Integer
Public sName As String
Public Sub New(ByVal sNum As Integer)
MyBase.New()
Me.sNum = sNum
End Sub
I've got a database class that I want to use to populate this.
Public Function populateStudent() As Object
Dim ObjStudent As New student(1)
ObjStudent.sName = "Bitz"
Return ObjStudent
End Function
Obviously this is just a step, eventually I'll be querying the database to populate the data, but I want to get this working first so I know I'm creating this correctly.
In my main class attached to my .aspx I want to be able to do
lblStudentName.Text = ObjStudent.sName
Am I going about this correctly, or is there a better way?
You need not have
MyBase.New()
because you don't have a explicit base class.
The return type of populateStudent() of Object does not make much sense; it should be either a list of Student if you are planning to return a collection of student after querying the db. if you are planning on populating the view from this method itself, then it should be a Sub returning nothing and not a Function.
Otherwise everything else looks okay.
EDIT:
Sounds like you need something like this.
Public Function populateStudent(Id as String) As student
Dim ObjStudent As New student(1)
ObjStudent.sName = "Bitz"
Return ObjStudent
End Function
Close. You'll want to set the .Text property on the Label control:
lblStudentName.Text = ObjStudent.sName
(which you have since edited your question to contain... it often bothers me that SO doesn't show that something was edited if the edit is very soon after the initial post)
As for a "better way" just remember that there are many, many ways to do just about anything. "Better" is very relative and depends on other factors not present in the code you have so far. As of now, you have a method which returns an instance of an object (similar to the Factory pattern, feel free to research more on that and other patterns) and you use properties on that object to populate data fields in the UI. Pretty straightforward, nothing wrong with it.
As the system grows and the problem domain becomes more complex, there will be more definition of "good design" vs. "bad design." But in just getting started, this is perfectly fine.
I have to send emails when a person receives a personal message on my website and for that I use a StringBuilder to create the HTML markup of the email.
also since it is required at many other places as well I have made a Shared Function (I am using VB.NET). now my only concern is that since shared functions are shared among all objects and maybe asp.net sessions, can it be possible that before one person email is being formed and another person access the same function, it would cause the data in the stringbuilder to be overwritten..
Currently my site doesn't have many users but can this become an issue in the future... Please advise me on this... Is there any better way or standard procedure to follow when using shared functions?
Also at one time I made the mistake of using a shared connection object and it would cause close if many people were to access it.
Shared functions can only access static/global variables as well as variable inside the function scope. So, if the the function is working with any number of static/shared resources then you need to synchronize between the calls to the function.
In your case, however, it doesn't sound like you're working with any shared resources, so it shouldn't be a problem.
Here's a case that illustrates the problem:
private static myCounter As Integer = 0
public shared function IncreaseCount() As Integer
myCounter += 1
for i as integer = 0 to 10 million
//'do extensive work
next
return myCounter
End Function
Imagine that you call the function for the first time, and you would expect it to return the number 1. But due to the fact that the function was called again before the first function call got to return the counter was increased once more, which means that both function calls return 2 instead of respectively 1 and 2. All the problem arrives when you want several things working on the same static resource.
Instead of using a static method you can have an EmailSender object attach to current HttpContext.This way each user will have its own EmailSender instance.
Here's the code in C# :
private static EmailSender _instance;
public static EmailSender GetEmailSender()
{
if(System.Web.HttpContext.Current != null)
{
if(! System.Web.HttpContext.Current.Items.ContainsKey("EmailSender"))
System.Web.HttpContext.Items["EmailSender"]=new EmailSender();\
return (EmailSender)System.Web.HttpContext.Current.Items["EmailSender"];
}
if(_instance==null)
_instance=new EmailSender();
return _instance;
}
It will work in web and windows application.
now every time you want to send an email you can do as follows:
GetEmailSender().SendMail(MailInfo mailInfo);
Also, if you're using VB.NET on Framework 3.5, you may want to look into using XML literals to build your HTML instead of StringBuilder. XML literals will make your code SUPREMELY more readable, and allow for very easy insertion of data into your message.
As a SIMPLE example...
Dim msg = <html><body>
Message sent at <%= Now.ToString() %>
</body></html>
myMailMessage.IsBodyHtml = True
myMailMessage.Body = msg.ToString()
Building a relatively simple website, and need to store some data in the database (mainly authentication, but there's some per-user stuff). I've worked on a couple of websites previously, and used database there too, but never liked the way I accessed the database.
The way I usually did this was by having a SqlMethods.cs, which basically was a static class with a whole lot of static methods such as bool CheckUserExistence(string username, string password) and SqlDataReader GetJobListings(int advertiserId), each of which was essentially "open connection, call a sproc, return what it returns". This approach seems un-natural to me, however. I cant quite put my mind to what I want it to look like, but this seems...weird.
So, my question is this: how do you access the database from your asp.net projects?
I am using SQL2005. I also dont think I'll need an ORM of any kind, since there really isnt that much to get from the DB, but maybe its easier with one? Suggest something.
Thanks!
Edit:I currently decided to just create a static class Sql that will have a number of sql-related methods (such as ExecuteReader(sprocName, params[]), etc) that will call the sproc with the given parameters and just return the DataReader.
Then, have classes for specific functionality, such as Authentication with methods like CheckUserExistence(username, password) and LogoffUser(session). These methods would just call Sql.ExecuteReader("sp_Auth_CheckUserExistence", _some_params_here_) and process the result as needed.
I don't know if thats good or bad, but it seems to work for me at the moment. Plus, I like the way it feels - its all nicely separated functionality-wise.
So, any more suggestions?
Check out Linq to SQL or Linq to Entities:
http://weblogs.asp.net/scottgu/archive/2007/05/19/using-linq-to-sql-part-1.aspx
http://msdn.microsoft.com/en-us/library/bb386964.aspx
The simplest way to do it is to create a data access class for each table in your database. It should have private variables and public properties for all of the columns in the table and the methods you describe should fill the internal variables (or use them to update the database).
Public Class MyTable
Private _id As Integer
Private _Name as String
Public ReadOnly Property ID As Integer
' Regular stuff here
End Property
Public Property Name As String
' Regular stuff here
End Property
Public Sub Load()
' Call SQL and get a data reader.
' Set _id and _Name from the data reader.
End Sub
End Class
Then, in your other code:
Dim mt As New MyTable
mt.Load()
' Now use mt.ID and mt.Name to access the data
What's the best way to view the data that LoadPostData event is loading to the controls in ASP.NET?
It's actually really simple. The NameValueCollection that get's passed to this method of EVERY control that implements the IPostbackDataHandler interface is the contents of Page.Request.Form. So you can access it at any time by getting a Watch on HttpContext.Current.Request.Form.
Ugh... I would suggest setting your IDE environment up to debug the .net framework, and set a breakpoint on the LoadPostData() method of Control. That's a bit heavy-handed, but if you're willing to wade through the recursive calls to the Control class (perhaps set a conditional breakpoint on the method?), you will be able to get to the data that way.
Good luck!
If you want to be sure you're looking at the data going into a particular control, you can subclass its control type and break during a custom implementation of IPostBackDataHandler.LoadPostData.
For example, you have a programmatically added control to collect the user's city. Change:
Public City As Textbox
to
Public City As BreakableLoadPostDataTextBox
Public Class BreakableLoadPostDataTextBox
Inherits TextBox
Protected Overrides Function LoadPostData( _
ByVal postDataKey As String, _
ByVal postCollection As System.Collections.Specialized.NameValueCollection) _
As Boolean
Return MyBase.LoadPostData(postDataKey, postCollection) ' Break here
End Function
End Class
Set a breakpoint on the Return call. When execution breaks, you should be able to see the postDataKey that's being used to read the control's new value out of the postCollection. You can of course augment this method to your heart's content with Trace calls and whatnot.