I’m moving an existing project over piece-by-piece. As I come across stumbling blocks I’m adding them to this post.

Code formatting

There isn’t the automatic formatting of code that you get with VB.NET in Visual Studio

Correct us of ToString

Error: Cannot convert method group ‘ToString’ to non-delegate type ‘string’. Did you intend to invoke the method?
When using the following code:

Regex.Replace(Regex.Replace(aString, aRegexPattern, "-"), "-{2,}", "-").ToString;

Cause:
.ToString without brackets is a property, I needed to call

.ToString()

No optional parameters on methods

You have to overload the method instead

Passing char into a method

Error: The best overloaded method match for ‘string.PadLeft(int, char)’ has some invalid arguments

Using:

aDate.Day.ToString().PadLeft(2, "0")

For some reason the char in the PadLeft needs to be wrapped in single quotes not double.

Fix:

aDate.Day.ToString().PadLeft(2, '0')

Parameters need to be exact

It’s a lot more picky about the types you pass into methods
In VB.NET I was getting away with passing a Double into Rectangle initialiser that actually wanted an int.

double outputHeight = 0;
double outputWidth = 0;

Rectangle rec = new Rectangle(0, 0, outputWidth, outputHeight);

Gives the error: The best overloaded method match for ‘System.Drawing.Rectangle.Rectangle(int, int, int, int)’ has some invalid arguments

Fixed with:

Rectangle rec = new Rectangle(0, 0, (int)outputWidth, (int)outputHeight);

Dividing 2 integers

Dividing 2 integers in VB.NET returns a Double.
But in C# the following returns zero:

int imageHeight = 768;
int imageWidth = 1024;
outputHeight =  imageHeight / imageWidth;

This works:

outputHeight =  (Double) imageHeight / (Double) imageWidth;

Saving a Bitmap

I was ensuring the Bitmap was saved with 100% quality like:

System.Drawing.Imaging.EncoderParameter qualityParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality,100);

I was getting an error “Parameter is not valid”. Finally traced it to the 100 parameter C# wanted it explicitly typed, using 100L

System.Drawing.Imaging.EncoderParameter qualityParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality,
<strong>100L</strong>);

Container.DataItem

<%#Container.DataItem["value"]%>

Gives the error: Cannot apply indexing with [] to an expression of type ‘object’

Fixed by changing to:

<# DataBinder.Eval(Container.DataItem, "value") %>

Case sensitivity!

Not working:

<%# container.findcontrol("filePhoto").clientid()%>

Working (Notice capital C, I and D in ClientID):

<%# Container.FindControl("filePhoto").ClientID%>

Request.QueryString

You need to change Request.QueryString(“carid”) to Request.QueryString["carid"]

Accessing a field in a DataRow

Using

hypSubSection.Text = drCar("car");

Gives the following error “‘drCar’ is a ‘variable’ but is used like a ‘method’”

It needs to be:

hypSubSection.Text = drCar["car"].ToString();

Raising events

Nice and easy in VB.NET
Declare the event:

Public Event cropped(ByVal aString As string)

Raise the event

RaiseEvent cropped("something")

In C# you need

    //declaring the event handler delegate
    public delegate void CropEventHandler(string aString);
    //declaring the event
    public event CropEventHandler cropped;

Then raise it with

     if (cropped != null)
        {
            cropped(paramsToPassBack);
        }

Debugging this cropped was always null. This turned out to be because nothing was listening to the event!
This doesn’t seem right to me, as the point of using a delegate is go make the object raising the event independent to any objects listening for the event.

A very easy way to stop this happening is to override the window.scroll function.
Add the following to the page with the form on.

<script type="text/javascript">
     window.scrollTo = function( x,y ) {
        return true;
    }
</script>

This is because the html that is rendered is a textarea instead on a regular input field.

Customvalidator to the rescue!

For example:

 <asp:TextBox runat="server" ID="txtIntro" TextMode="MultiLine" Rows="3" />
 <asp:CustomValidator runat="server" ID="cvIntro" maxlength="255"
	ErrorMessage="Please enter 255 characters or less"
	ControlToValidate="txtIntro"
	ClientValidationFunction="checkTextAreaLength" />

This “fires” this clientside function:

<script type="text/javascript">
    function checkTextAreaLength(source, arguments) {
        var maxlength = $(source).attr("maxlength");
        if (maxlength == undefined) maxlength = 255;
        if (arguments.Value.length > maxlength)
            arguments.IsValid = false;
        else
            arguments.IsValid = true;
    }

</script>

One thing to note is that I’ve had to add the maxlength attribute to the customvalidator not to the textbox.  I would prefer to have maxlength set on the textbox but so far I’ve been unable to work this out.  If anyone has any ideas please let me know.

e.g.

<label for="emailaddress">Email</label>
<input type="text" id="emailaddress"/>

Now if you’re referencing asp.net controls you can use the clientid property.

e.g.

<label for="<%= emailaddress.clientid()%>">Email</label>
<asp:TextBox runat="server" ID="emailaddress" />

All nice an easy so far. The situation gets a little bit more complicated when you start nesting this inside a repeater.

e.g.

<asp:Repeater runat="server" ID="rpt1">
<itemTemplate>

<label for="<%= emailaddress.clientid()%>">Email</label>
<asp:TextBox runat="server" ID="emailaddress" />

</itemTemplate>
</asp:Repeater>

this won’t work.
Here’s what you need to do instead.

<asp:Repeater runat="server" ID="rpt1">
<itemTemplate>

<label for="<%# container.findcontrol("emailaddress").clientid()%>">Email</label>
<asp:TextBox runat="server" ID="emailaddress" />

</itemTemplate>
</asp:Repeater>

As an asp.net developer and jQuery advocate I know I’m going to find this tip very useful

http://devoma.com/post/JQuery-and-ASPNET-validators.aspx

It’s best practice to turn off viewstate for the whole page or for individual usercontrols if they don’t require viewstate.  The deciding factor here is: does the page or usercontrol perform postbacks.

Even with careful pruning of viewstate you’ll probably find your viewstate is still large…

What you can do

Now there are a couple of strategies I’ve seen for working round this, both involve overriding the page

1 is to intercept the page rendering and move the viewstate hidden variable to the bottom of the page.

Here’s an example http://www.dotnetdiary.com/labels/Moving%20ViewState%20Field.html

2 is a very clever solution that keeps the viewstate information on the server and justs passes a key back and forth to the client.

I read about this approach here http://www.eggheadcafe.com/articles/20040613.asp

Here’s my approach

Now since I don’t think that viewstate bloat has too much of an impact on page performance for real users I’m only going to worry about search engine spiders.

asp.net has a way of detecting spiders – now I’m not saying it’s going to be 100% accurate but in my tests it’s been accurate enough for this technique.

In the page load of your page (or master page)

If Request.Browser.Crawler Then Page.EnableViewState = False

er that’s it, pretty simply eh?

You can verify if this is working by viewing the source of the cached version of the page that google holds.

Hope that helps!

My button (server-side) was pumping out a bit of javascript 

Page.ClientScript.RegisterStartupScript(GetType(String),
         "loginunsuccessful", "<script type=""text/javascript"">
         alert('Login unsuccessful – please try again');</script>")

And this kept causing the error.

I tried using the prescribed fix: ClientScript.RegisterForEventValidation(mycontrol.uniqueid) in the prerender.  Still got the error.

Here’s how I fixed it.  RegisterStartupScript does the job of running at startup by emiting the js right at the foot of the page.  I wrapped my JS in jQuery’s own onload code.

Page.ClientScript. RegisterStartupScript(GetType(String),
          "loginunsuccessful", "<script type=""text/javascript"">
          $(document).ready(function(){alert('Login unsuccessful – please try again');});
          </script>")

Still the same error, I then changed to using Page.ClientScript.RegisterClientScriptBlock, which emits the JS in the midst of the html and hey presto no errors.  This is without using the RegisterForEventValidation I’d like to add.

Final code:

Page.ClientScript.RegisterClientScriptBlock(GetType(String),
          "loginunsuccessful", "<script type=""text/javascript"">
          $(document).ready(function(){BlockAlert('Login unsuccessful – please try again');});
          </script>")

Simple to fix when you know how.

In your ashx change

Public Class yourclass :     Implements IHttpHandler

    Implements SessionState.IRequiresSessionStat

to

Public Class yourclass

Implements IHttpHandler

    Implements SessionState.IRequiresSessionStat

The way to do this is to use a custom validator.

Important note: you need to set validateemptytext=”true” otherwise it doesn’t fire

Then add the following javascript (note that I’m using jQuery here to reference the validator control)

<script type="text/javascript">// <![CDATA[
function ValidateContentText(source,args)
{
var controltovalidate = jQuery(source).attr("controltovalidate");
var fckControl = FCKeditorAPI.GetInstance(controltovalidate);
args.IsValid = fckControl.GetXHTML(true) != "";
}
// ]]></script>

You might also want to handle the server-side validation too, even though if client-side isn’t working then the fckeditor won’t be working…

Protected Sub cvIntro_ServerValidate(ByVal source As Object, ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs) Handles cvIntro.ServerValidate

Dim myContentPlaceHolder As ContentPlaceHolder

myContentPlaceHolder = CType(Master.FindControl("cphMain"), ContentPlaceHolder)

Dim fckEditorToCheck As FredCK.FCKeditorV2.FCKeditor

fckEditorToCheck = myContentPlaceHolder.FindControl(CType(source, CustomValidator).ControlToValidate)

args.IsValid = Not String.IsNullOrEmpty(fckEditorToCheck.Value)

End Sub

Update 2011

var controltovalidate = jQuery(source).attr("controltovalidate");

No longer works... just use

var controltovalidate = source.controltovalidate;

Instead - easy peasy

me.findcontrol("fckEditor")

But unfortunately that doesn’t work.
You need to make a reference to the place holder the control is in, then find the control within the place holder.
Another gotcha here is that you need to find this control based on the id it has on the master page not the id it has in the page in question.
e.g.
If the tags on the page are

<asp:Content ID="Content2" ContentPlaceHolderID="cphMain" Runat="Server">
</asp:Content>

You need to create a reference to the place holder with

Dim myContentPlaceHolder As ContentPlaceHolder
myContentPlaceHolder = CType(Master.FindControl("cphMain"), ContentPlaceHolder)

and not

Dim myContentPlaceHolder As ContentPlaceHolder
myContentPlaceHolder = CType(Master.FindControl("Content2"), ContentPlaceHolder)

Hope that saves someone some time!