KoenV

.NET and SMTP Configuration

2010-12-06T12:53:06Z

Sometimes I feel stupid about discovering .NET features that have been there since an old release (2.0 in this case)...

Apparently you can just use this configSecion “mailSettings” and never have to configure your SmtpClient instance in code again (no, not hard-coded):

<system.net>
    <mailSettings>
        <smtp deliveryMethod="Network" from="My Display Name <myname@mydomain.com>">
            <network host="mail.server.com" />
        </smtp>
    </mailSettings>
</system.net>

Now you can go all like:

new SmtpClient().Send(mailMessage);

…and everything is configured for you, even the from address (which you can obviously override).

Visual Studio 2010 tip: Cut empty lines

2010-06-17T14:38:37Z

How many times you wanted to move 2 lines by cut and pasting them, but the line you cut last is actually a blank line and your actual code is removed from the clipboard? Visual Studio 2010 has an option that keeps cutting blank lines from overwriting the clipboard. Go and uncheck this one: Tools » Options » Text Editor » All Languages » General » Apply Cut or Copy commands to blank lines when there is no selection

Extra (related) tip

The (free) Visual Studio 2010 extension Visual Studio 2010 Pro Power Tools contains (apart from a bunch of other handy features) the commands Edit.MoveLineUp and Edit.MoveLineDown to do whatever they say they do and maps them automatically to keyboard shortcuts Alt+Up & Alt+Down.

Resharper (not-free) has similar commands for moving lines, by default mapped to Ctrl+Alt+Shift+Up/Down.

AgUnit - Silverlight unit testing with ReSharper

2010-05-31T08:10:32Z

If you’re a ReSharper user and Silverlight 4 developer you’ll probably like this add-in that two of my co-workers created. It lets you run your Silverlight unit tests inside the Visual Studio IDE.

You can get the add-in from Codeplex: http://agunit.codeplex.com/

(requires ReSharper 5 and Silverlight 4)

Generically correcting data before save with Entity Framework

2010-05-28T12:04:00Z

Been working with Entity Framework (.NET 4.0) for a week now for a data migration job and needed some code that generically corrects string values in the database. You probably also have seen things like empty strings instead of NULL or non-trimmed texts ("United States ") in "old" databases, and you don't want to apply a correcting function on every column you migrate.

Here's how I've done this (extending the partial class of my ObjectContext):

public partial class MyDatacontext
{
    partial void OnContextCreated()
    {
        SavingChanges += OnSavingChanges;
    }

    private void OnSavingChanges(object sender, EventArgs e)
    {
        foreach (var entity in GetPersistingEntities(sender))
        {
            foreach (var propertyInfo in GetStringProperties(entity))
            {
                var value = (string)propertyInfo.GetValue(entity, null);

                if (value == null)
                {
                    continue;
                }

                if (value.Trim().Length == 0 && IsNullable(propertyInfo))
                {
                    propertyInfo.SetValue(entity, null, null);
                }
                else if (value != value.Trim())
                {
                    propertyInfo.SetValue(entity, value.Trim(), null);
                }
            }
        }
    }

    private IEnumerable<object> GetPersistingEntities(object sender)
    {
        return ((ObjectContext)sender).ObjectStateManager
            .GetObjectStateEntries(EntityState.Added | EntityState.Modified)

            .Select(e => e.Entity);
    }

    private IEnumerable<PropertyInfo> GetStringProperties(object entity)
    {
        return entity.GetType().GetProperties()
            .Where(pi => pi.PropertyType == typeof(string));
    }

    private bool IsNullable(PropertyInfo propertyInfo)
    {
        return ((EdmScalarPropertyAttribute)propertyInfo

            .GetCustomAttributes(typeof(EdmScalarPropertyAttribute), false)
            .Single()).IsNullable;
    }
}

Obviously you can use similar code for other generic corrections.

Error pages in ASP.NET

2010-05-18T11:37:00Z

In ASP.NET you can retrieve the last unhandled exception via:

(HttpContext.Current.)Server.GetLastError() // Server object is available as a property in Page and UserControl context

This obviously only works in the same roundtrip. If you want to retrieve this information in your error page, you got a problem because the error page is not returned in the same roundtrip. The server responds with a redirect response and a new request to the error page is automatically sent. A common workaround would be to store the exception in your Session state from the Application_Error event in Global.asax.

From ASP.NET 3.5 you can configure the redirect mode for error pages:

This way the redirect response is not sent and the error page is returned right away. That implies that the browser is not aware of a page change and cannot reflect it in the address bar, so your original URL is not replaced with the URL of the error page, which might be what you actually want…

VTM goes Surface

2009-06-08T16:15:00Z

My colleague Kristof wrote an article about a Surface project he did for VTM (Belgian national television) and it was used during yesterdays' election show.

DataSource parameter for code-behind property

2009-02-03T10:19:00Z

Here's some code for a server control "PropertyParameter" that you can use as a SelectParameter in your xyzDataSource that binds (one-way!) to a property value that is defined in code behind. This is something I need sometimes and isn't available out-of-the-box.

This method uses reflection and requires the property in code-behind to be public. There are two implementations, one for a Page and one for a UserControl. You will need to specify the Target property if you use it inside a UserControl.

This is how you use it in your markup:

<asp:ObjectDataSource ID="StatusObjectDataSource" runat="server"

    TypeName="Components.WorkflowSecurity.WorkflowComponent"

    SelectMethod="GetAvailableStatusesForEntityType">

    <SelectParameters>

        <controls:PropertyParameter Name="entityType"

            PropertyName="EntityType" Target="Page" />

    </SelectParameters>

</asp:ObjectDataSource>

Here is the the code for the server control:

public class PropertyParameter : Parameter

    public enum PropertyTargetEnum

        Page,

        UserControl

    public string PropertyName { get; set; }

    public PropertyTargetEnum Target { get; set; }

    public PropertyParameter()

        Target = PropertyTargetEnum.Page;

    protected override object Evaluate(

        HttpContext context, Control control)

        if (string.IsNullOrEmpty(PropertyName))

            throw new ArgumentNullException("PropertyName");

        Control targetControl = ResolvePropertyTarget(control);

        Type pageType = targetControl.GetType();

        PropertyInfo pi = pageType.GetProperty(PropertyName,

            BindingFlags.Instance |

            BindingFlags.Public |

            BindingFlags.NonPublic);

        if (pi == null)

            throw new InvalidOperationException(

                string.Format("Property '{0}' not found on {1}.",

                PropertyName, Target));

        return pi.GetValue(targetControl, null);

    private Control ResolvePropertyTarget(Control control)

        switch (Target)

            case PropertyTargetEnum.Page:

                return control.Page;

            case PropertyTargetEnum.UserControl:

                return FindParentUserControl(control);

        throw new ArgumentException("Invalid target type.");

    private UserControl FindParentUserControl(Control control)

        Control parent = control.Parent;

        while (parent != null)

            if (parent is UserControl)

                return (UserControl)parent;

            parent = parent.Parent;

        throw new ArgumentException(string.Format(

            "'{0}' is not inside a UserControl.",

            control.ID));

Btw, there are two common workarounds if you don't like this implementation:

Store the value in a HiddenField and use a ControlParameter instead
Add a Parameter control; implement the OnSelecting event of the DataSource to set the value on the InputParameters collection

Warning: Generation of designer file failed: The ... tag has already been registered.

2008-12-02T12:52:00Z

Weird problem in ASP.NET again... With a weird solution:

In my apps I always have a folder UserControls where I put UserControls (not custom or server controls) that I use throughout the site. Examples are a date textbox with validation, formatted labels, upload fields, toggled image buttons, error message labels, etc. I register all these controls globally in the web.config pages section, like this:

<pages>
    <controls>
        <add tagPrefix="myapp" tagName="WebUserControl1" 
             src="~/UserControls/WebUserControl1.ascx"/>
        <add tagPrefix="myapp" tagName="WebUserControl2" 
             src="~/UserControls/WebUserControl2.ascx"/>
    </controls>
</pages>

The problem is that some user controls also use another user control from that same folder, which leads to the following ASP.NET parser error:

Parser Error Message: The page '/UserControls/WebUserControl1.ascx' cannot use the user control '/UserControls/WebUserControl2.ascx', because it is registered in web.config and lives in the same directory as the page.

The solution for that is to add a @Register directive to WebUserControl1.ascx like this:

<%@ Register TagPrefix="myapp" TagName="WebUserControl2" Src="~/UserControls/WebUserControl2.ascx" %>

But now I get the error from the blog post title, so if I add new controls to the user control, the designer file is not updated and I cannot access these in code behind (unless I update the designer file manually - NOT).

The key to resolve is to either pick a different TagPrefix or TagName in the @Register directive and use it like that, e.g.:

<%@ Register TagPrefix="myappLocal" TagName="WebUserControl2" Src="~/UserControls/WebUserControl2.ascx" %>
<myappLocal:WebUserControl2 runat="server" />

<%@ Register TagPrefix="myapp" TagName="WebUserControl2Local" Src="~/UserControls/WebUserControl2.ascx" %>
<myapp:WebUserControl2Local runat="server" />

Now the designer file keeps updating...

Exceptional exception handling

2008-10-08T17:59:00Z

My (much more productive) colleague Davy beat me to post this problem we had today at work, so I'm gonna be lazy and link to him (and steal his title).

Btw yesterday we applied this "solution" to one of our biggest projects and -hooray- it worked...

LINQPad

2008-03-17T11:32:00Z

Joseph Albahari created this great tool to execute LINQ (but also SQL) queries and review the results. In case of LINQ you also get to see the corresponding compiler translation and SQL query.

Some pro's:

Great for testing LINQ without having to build and debug your entire application in Visual Studio...
No installation (just exe)
Self updating
You can choose between C# and VB
Includes query organizer
...

Get it here: www.linqpad.net

PS: Also take the LINQ quiz here: www.albahari.com/nutshell/linqquiz.html

Quick Attach and Detach Debugger

2008-02-14T09:13:00Z

Here's a trick I often use in Visual Studio to speed up the trial-and-error process.

A disadvantage of using an ASP.NET Web Application Project instead of an ASP.NET Web Site is that you cannot edit code behind files (or basically any code file in your web project) while you are debugging. So to edit just minor things there, you need to stop the debugger (which closes the browser typically), edit, compile and start the debugger again, which could take some time.

I have written (recorded and adjusted) a small VS macro that attaches the debugger for me. It will actually look if the VS built-in webserver is active. If not it will attach to IIS.

Sub AttachDebugger()
  Try
    Dim dbg2 As EnvDTE80.Debugger2 = DTE.Debugger
    Dim trans As EnvDTE80.Transport = dbg2.Transports.Item("Default")
    Dim dbgeng(1) As EnvDTE80.Engine
    dbgeng(0) = trans.Engines.Item("Managed")
 
    Dim proc2 As EnvDTE80.Process2
    Try
      proc2 = dbg2.GetProcesses(trans, "").Item("WebDev.WebServer.EXE")
    Catch ex As Exception
      proc2 = dbg2.GetProcesses(trans, "").Item("w3wp.exe")
    End Try
 
    proc2.Attach2(dbgeng)
  Catch ex As System.Exception
    MsgBox(ex.Message)
  End Try
End Sub

Copy this in one of your Macro modules and it should compile. The script could be a bit different on Windows XP, because the ASP.NET process is called "aspnet_wp" there...

And then assign shortcuts to your macro. For detaching you don't need a macro, it's a built-in command. My shortcut's are Ctrl+Shift+A for attaching and Ctrl+Shift+D for detaching.

Now you can detach your debugger (leaving the browser open), edit the code, build it (only build what you changed), attach and refresh the browser...

Checkboxes in Windows Explorer

2008-02-13T20:38:00Z

Here's a Vista feature some people have asked me about, the mysterious checkboxes... (Total Commander users: continue reading at your own risk :o)

How does it work?

The checkboxes appear when you have selected a file/folder or when you hover it
When you click on the file/folder name or icon, the selection changes to that file/folder (clearing the previous selection)
When you click the checkbox, the file/folder is added to the current selection (without holding Ctrl or Shift)
Works in any view mode (details, list, icons, thumbnails,...) although I haven't seen it in the command prompt...

Where to get it?

Go to the Folder Options (can't think of the easiest way to get there but you should have it by now)
Go to the View tab
Scroll to the bottom
Check this one: Use check boxes to select items
View tab" alt="Folder options > View tab" hspace=5 src="http://weblogs.asp.net/blogs/koenv/folderoptions.JPG" align=top vspace=5 border=0 mce_src="http://weblogs.asp.net/blogs/koenv/folderoptions.JPG">

Now you'll never have to drop your sandwich again to hold the shift key!

CS0426: The type name 'Web' does not exist in the type 'ASP....

2008-02-12T17:03:00Z

I've been having this problem with ASP.NET themes that block my web applications from working. I always get this error when opening any page: CS0426: The type name 'Web' does not exist in the type 'ASP.Foo'.

When I set the default language to vb (web.config > compilation tag), the exception message is even more cryptic: BC30002: Type 'Foo.Web.WebControls.MyWebControl' is not defined.

The problem was that I always use the following project setup:

Foo.Web: class library project containing web controls, base master pages, base pages, base user controls,...
Foo.WebApplication: web application project that references Foo.Web. I also register the controls globally in web.config (<pages><controls><add tagPrefix="foo" assembly="Foo.Web" namespace="Foo.Web.WebControls" />...) but the problem is also there if you register your controls locally.
Then in Foo.WebApplication I have defined a theme named "Foo" (in the App_Themes folder). I configure this theme globally in web.config (<pages styleSheetTheme="Foo">) but that shouldn't matter where it is configured.
In that theme I have a skin file (or several) that style one of my web controls from the Foo.Web project.

The problem is that at runtime the theme Foo is compiled in a namespace ASP.Foo, and then it will look for the namespaces Web.WebControls below that one, which isn't what I want. The only solution that I found is renaming the theme to something different, e.g. FooStyle.

I'm not sure whether this problem can also occur if you have an ASP.NET website, but I guess

Operator overloading and testing for null

2008-01-24T23:54:00Z

Operator overloading in C# is basically writing a public static method, like this:

public static bool operator ==(CustomObject object1, CustomObject object2)
{
return object1.SomeProperty == object2.SomeProperty;
}

Before you do this, it is necessary to check if both parameters are not null, otherwise you will get a NullReferenceException when doing this:

CustomObject object1 = GetCustomObject();
if (object1 == null)

But you cannot do the following because it will simply recurse the evaluation to the same method, and give you a StackOverflowException:

public static bool operator ==(CustomObject object1, CustomObject object2)
{
    if (object1 == null || object2 == null)
    {
        //...

Instead you can cast your parameters to "object"s before evaluating, which will use the == operator for Object:

if ((object)object1 == null || (object)object2 == null)

Also, if you don't want to repeat the whole bunch again for the != operator, you can simply write this:

public static bool operator !=(CustomObject object1, CustomObject object2)
{
return !(object1 == object2);
}

Kick-off post

2008-01-24T23:26:00Z

I've been having this idea about a blog for a while now. Basically because I often run into a problem that I had before but then it's still hard to figure out how I fixed it back then. Now this will be my little public howto-database.

I'll try to post several bits a week about various topics of software development, but mainly about web development, ASP.NET, scripting,...

Thanks to Joe and the rest of the www.asp.net team for opening up some space for us...