.NET Tip of The Day.org

Send an e-mail any time an unhandled exception occurs

Sat, 10 May 2008 14:06:58 GMT

Consider using built-in ASP.NET health monitoring to monitor your website. Especially if you are not monitoring it at all yet. ASP.NET health monitoring contains ready-to-use Web health-monitoring events classes (Web events) and health-monitoring providers (listeners). For example, you can easily configure it to send an email any time an error is detected.

News: .NET Tips & Tricks Community RSS

Sat, 10 May 2008 15:57:00 GMT

Those who prefer reading this site through RSS now can also subscribe for updates to .NET Tips & Tricks Community.

News: Why does new tips appear on this site so infrequently?

Thu, 08 May 2008 00:48:00 GMT

Hi guys. I know some of you are not satisfied with the frequency new tips appear on this site. The last comment I received was a proposal to rename the site to .NET Tip of The Month :) But I don't want to do this because I'm going to fix this problem. I'm working on the .NET Tips & Tricks Community section now. My tips that are too small to hit the front page were added to this section. It's the place where all of you can share your .NET tips and tricks.

It's clear that this section lacks for some features. And if anyone out of 2510 subscribers has a proposal, just drop me a line. My email is kostya.ly@gmail.com.

Thanks for you patience.
Kostya Ly

Turn off Session State if you're not using it

Thu, 01 May 2008 23:51:00 GMT

Since ASP.NET Session State is on by default, you pay the cost in memory even if you don't use it. If you're not using Session State, turn it off and save yourself the overhead. There are serveral ways to do this:

If you're not using Session State at all, turn it off completely via web.config file:

<system.web>

<sessionState mode="Off"></sessionState>

...
If you're using Session State, but it's required only for a few pages, then first turn it off for all pages:

<system.web>

<pages enableSessionState="false">

...

then enable it for a specific page:

<%@ Page ... EnableSessionState="true" %>

P.S. obviously such optimization makes sense only for high-traffic web sites.

How to debug Windows Service startup

Wed, 16 Apr 2008 22:05:00 GMT

Actually you can use this trick every time when:

You want to debug a process startup.
You can't run the process by hitting F5 in Visual Studio (for example, Windows Service).

So the problem is that you can't simply attach the Visual Studio debugger to the process as there isn't one to attach to until after you start the process. However, once you start the process if you have a bug such as an exception in the process's initialization you won't get the debugger attached to the process before it's too late.

Calling Debugger.Launch() or Debugger.Break() in your code allow you to debug such problems. This methods pop up the following screen asking you which instance of the debugger it should use to debug the application.

How to change HTML markup produced by ASP.NET controls

Wed, 09 Apr 2008 13:07:00 GMT

There are at least two ways of changing HTML markup produced by standard ASP.NET controls. The most obvious one is to derive a new class based on an existing ASP.NET control class and override the necessary rendering methods.

Another option that is worth considering is to write a small control adapter for the existing ASP.NET control. This is a little chunk of logic that you add to your web site to effectively "adapt" an ASP.NET control to render the HTML you prefer. This approach has the following two major advantages over custom controls:

You don't need to add the @Register directives to your pages.
The ASP.NET framework comes with a built-in means to apply the adapters to just certain browsers. When you build entirely new custom controls you have to write your own logic to handle browser detection to vary the response.

For example you can use ASP.NET 2.0 CSS Friendly Control Adapters package to generate CSS friendly markup from some of the more commonly used ASP.NET controls.

Label to a form input field

Tue, 01 Apr 2008 23:15:00 GMT

If you set a label to a form element set the AssociatedControlID property. This will force the label to render as <label> rather than <span>. A benefit of using the AssociatedControlID property is that clicking a label when this property is set automatically changes the form focus to the associated form input.

News: .NET Tips & Tricks Community (ALPHA)

Mon, 24 Mar 2008 00:16:00 GMT

Some of you have used "Add a tip" function and submitted one or more tips. Some of these tips are pretty interesting and I publish them on this site. But for someone other submitted tips could be interesting as well. So, from now on, everybody can check out all tips submitted by the visitors of the site in a new section - .NET Tips & Tricks Community (ALPHA). In fact this is not a real community yet (that's why you can see ALPHA in it's name). I'll add some common features soon. Let's see how it goes.

Add Windows Explorer to your Visual Studio tools menu

Mon, 17 Mar 2008 18:15:00 GMT

I often need to open Windows Explorer and browse to the current file, folder, or project that I am working on in Visual Studio. This tip allows you to achieve this by clicking "Windows Explorer" in the Tools menu, and is one of the most simple-yet-useful tips I know of.

To set it up, click Tools, then External Tools..., then click Add. Now enter the following data:
Title: Windows Explorer
Command: explorer.exe
Arguments: /select,"$(ItemPath)"

Leave Initial directoy blank, and click OK. Now when you click Tools, Windows Explorer, Windows Explorer will open with the current file you are editing selected.

submitted by Daniel Flower

Correct event invocation

Sat, 01 Mar 2008 18:18:00 GMT

Be aware that if there are no subscribers a .NET event will be null. Therefore when raising the event from C# test it for null first.

    public event EventHandler SelectedNodeChanged;
 
    protected virtual void OnSelectedNodeChanged(object sender, EventArgs e)
    {
        //Event will be null if there are no subscribers
        if (SelectedNodeChanged != null)
        {
            SelectedNodeChanged(this, e);
        }
    }

However in multithreaded application the last subscriber can unsubscribe immediately after the null check and before the event is raised. To avoid a null reference exception make a temporary copy of the event.

    public event EventHandler SelectedNodeChanged;
 
    protected virtual void OnSelectedNodeChanged(object sender, EventArgs e)
    {
        //Make a temporary copy of the event to avoid possibility of
        //a race condition if the last subscriber unsubscribes
        //immediately after the null check and before the event is raised.
        EventHandler handler = SelectedNodeChanged;
 
        //Event will be null if there are no subscribers
        if (handler != null)
        {
            handler(this, e);
        }
    }

submitted by Sergey P.

How to view code that is covered by the IntelliSense pop-up

Fri, 22 Feb 2008 12:56:00 GMT

When working in Visual Studio 2008 and the IntelliSense pop-up is visible, but you would like to view the code that is covered by it, press and hold the Ctrl key, and the pop-up becomes transparent so that you can view the code that is below the pop-up.

When returning DataReader from a function, specify CommandBehavior.CloseConnection

Sat, 16 Feb 2008 15:30:00 GMT

When you create an ADO.NET DataReader object, specify the CommandBehavior.CloseConnection enumeration in your call to ExecuteReader. This ensures that when you close the DataReader, the SQL connection is also closed. This is especially helpful when you return a DataReader from a function, and you do not have control over the calling code. If the caller forgets to close the connection but closes the reader, both are closed when the DataReader is created by using CommandBehavior.CloseConnection. This is shown in the following code fragment.

    public SqlDataReader CustomerRead(int CustomerID)
    {
        //... create connection and command, open connection
        return myCommand.ExecuteReader(CommandBehavior.CloseConnection);
    }
 
    //... client code
    SqlDataReader myReader = CustomerRead(10248);
    //... read some data
    myReader.Close(); // reader and connection are closed

Use explicit casting instead of DataBinder.Eval

Tue, 12 Feb 2008 21:42:00 GMT

The DataBinder.Eval method uses .NET reflection to evaluate the arguments that are passed in and to return the results. Consider limiting the use of DataBinder.Eval during data binding operations in order to improve ASP.NET page performance.

Consider the following ItemTemplate element within a Repeater control using DataBinder.Eval:

   <ItemTemplate>
       <tr>
           <td><%# DataBinder.Eval(Container.DataItem, "field1") %></td>
           <td><%# DataBinder.Eval(Container.DataItem, "field2") %></td>
       </tr>
   </ItemTemplate>

Using explicit casting offers better performance by avoiding the cost of .NET reflection. Cast the Container.DataItem as a DataRowView:

   <ItemTemplate>
       <tr>
           <td><%# ((DataRowView)Container.DataItem)["field1"] %></td>
           <td><%# ((DataRowView)Container.DataItem)["field2"] %></td>
       </tr>
   </ItemTemplate>

Consider using weak references for your custom caching solutions

Wed, 06 Feb 2008 21:51:00 GMT

Consider using weak references when you implement a custom caching solution, so that cached objects can be released by garbage collection when there is memory pressure. You should use weak references mostly for objects that are not small in size because the weak referencing itself involves some overhead. They are suitable for medium to large-sized objects stored in a collection.

Automatically insert attribute value quotes

Mon, 04 Feb 2008 20:50:00 GMT

Visual Studio HTML/ASPX editor can save you some time if you enable option Tools | Options... | Text Editor | HTML | Format | Insert attribute value quotes when typing. When this option is enabled, once you type a name of an attribute and following "=" symbol, Visual Studio automatically inserts a pair of quotes and invokes IntelliSense menu. After that you need only to select an attribute value from the menu and hit the Enter button. It's another nice timesaver.

Correct using of ASP.NET Cache

Wed, 30 Jan 2008 16:20:00 GMT

Often in ASP.NET application we see a code which looks like this one:

    if (Cache["SomeData"] != null)
    {
        string name = ((SomeClass)Cache["SomeData"]).Name;
        //.....
    }

This code is not safe enough and the second statement can generate a NullReferenceException sometimes. There is no guaranttee that a cached object will stay in the cache between two calls. After the first call it can be deleted either by garbage collector or by another thread to refresh cached data.

So to overcome this problem rewrite the code using as operator:

    SomeClass someClass = Cache["SomeData"] as SomeClass;
    if (someClass != null)
    {
        string name = someClass.Name;
        //.....
    }

via Dmytro Shteflyuk

Treat .NET Threads as a shared resource

Tue, 22 Jan 2008 01:21:00 GMT

Do not create .NET threads on a per-request basis because this can severely impact scalability. Creating new threads is also a fairly expensive operation that should be minimized. Treat threads as a shared resource and use the optimized .NET thread pool.

How to create fully qualified URLs

Fri, 18 Jan 2008 13:47:00 GMT

With ASP.NET it's quite easy to get absolute path to a page by calling the VirtualPathUtility.ToAbsolute method. Getting absolute URL is not that obvious but still quite easy. Just combine request url with absolute path to your ASP.NET page:

string absolutePath = VirtualPathUtility.ToAbsolute("http://dotnettipoftheday.org/test/MyWebForm.aspx");
Uri newUri = new Uri(Request.Url, absolutePath);

COALESCE function instead of long CASE WHEN ... ELSE (T-SQL)

Tue, 15 Jan 2008 22:00:00 GMT

Instead of using long "SELECT ... CASE WHEN ... ELSE ..." construction, you can use the COALESCE function when you need to find a value that is not NULL. Lets review the following T-SQL expression, in which we need to select an available "source":

SELECT TheSource =
   CASE
      WHEN localSource IS NOT NULL THEN localSource
      WHEN intranetSource IS NOT NULL THEN intranetSource
      WHEN internetSource IS NOT NULL THEN internetSource
      ELSE ''
   END
FROM ...

Now lets rewrite the code above using COALESCE function:

SELECT TheSource =
   COALESCE(localSource, intranetSource, internetSource, '')
FROM ...

The tip applies to MS SQL Server 2000/2005.

Cut a line into memory

Sun, 13 Jan 2008 12:13:00 GMT

While in Visual Studio.NET source code editor, press Ctrl+L to cut a line of code into memory. This is an easy way to move lines around your pages, or delete a set of lines quickly. Simple, yet useful!

submitted by Grant Merwitz, The X-Box Lounge

How to check email works without using SMTP

Tue, 08 Jan 2008 22:15:00 GMT

Testing code that sends email has always been a pain. You had to set up a SMTP service just to test that your .NET application sends the e-mail correctly.

However, there is a way to send e-mails with no SMTP server set up. Just configure your .NET application to drop e-mails into a specified folder instead of sending them via SMTP server:

<system.net>
   <mailSettings>
      <smtp deliveryMethod="SpecifiedPickupDirectory">
         <specifiedPickupDirectory pickupDirectoryLocation="c:\Test\" />
      </smtp>
   </mailSettings>
</system.net>

This will instruct SmtpClient class to generate mail message, save it as .eml file and drop it into c:\Test\ folder.

A simple method to validate an integer, double, date, and currency values entered into a textbox on ASP.NET page

Sat, 05 Jan 2008 23:59:00 GMT

Normally the CompareValidator is used to check one value against another on ASP.NET page. However it also can be used to ensure user has entered data in a correct format.

Here's how it works:

Set the ControlToValidate property to the ID of the TextBox.
Set the Operator property to DataTypeCheck.
Assign a ValidationDataType enumeration member to the Type property, which includes String, Integer, Double, Date, and Currency.

Note: this method is culturally sensitive. This means that if you change your browsers settings to en-UK, a date of 1-28-01 correctly fires the validator, while 28-1-01 is allowed through. This is because the date format is day-month-year in that region.

What is the difference between UriBuilder.ToString and UriBuilder.Uri.ToString

Wed, 26 Dec 2007 23:30:00 GMT

UriBuilder.ToString - the resulting string always contains Port, even if it is the default port for the Scheme. For example - http://localhost:80/tips.
UriBuilder.Uri.ToString - the resulting string only contains the port if it is not the default port for the scheme. For example - http://localhost/tips.

Therefore, in most of the cases UriBuilder.Uri.ToString should be used to omit redundant port specification.

Visual Studio Bookmarks

Fri, 21 Dec 2007 17:01:00 GMT

Bookmarks can be used to mark places in the code, like the code that you might want to jump back and forward. Bookmarks can be related to task list shortcuts, kind of the same functinality.

The bookmarks can be setup very easy, by pressing Ctrl+K, Ctrl+K to leave bookmark.

For navigation, you can press Ctrl+K, Ctrl+N to move to the next bookmark, or Ctrl+K, CTRL+P for the previous bookmark. It's easy, just try it now.

Generating compiler warnings for calls to an obsolete methods

Sat, 15 Dec 2007 01:17:00 GMT

Throughout the product development cycle, occasionally certain methods become obsolete. If you can't modify those methods, will need to write another implementation of the method using a slightly different name or signature. To maintain compatibility, you do not want to remove the old method and break your code. This is where the .NET Obsolete attribute comes in handy:

    [Obsolete("Use the new LogRequestEx instead.")]
    public static void LogRequest(string feedUrl, string referer)
    {
        ...

Setting the Obsolete attribute as above makes a warning message appear in the Visual Studio's Error List stating that the particular call to a method is obsolete. The warning message also includes your personalized message that you pass as the attribute's argument (such as, "Use the new LogRequestEx instead").

Big solutions can be organized using Solution Folders

Fri, 07 Dec 2007 19:55:00 GMT

Here is an example of a big Visual Studio.NET solution that contains numerous projects:

Such a big Visual Studio.NET solutions can be organized by grouping related projects into folders. Just right-click on the solution node and choose Add | New Solution Folder to add a Solution Folder. Then just Drag'n'Drop projects into this folder.

This also will allow you to do some operations on a group of projects. For example, unload all projects in a Solution Folder, collapse or hide entire Solution Folder so that you can work easily in Solution Explorer in Visual Studio.NET.

How to change the default view for Web pages and WinForms in Visual Studio

Wed, 05 Dec 2007 17:20:00 GMT

By default Visual Studio.NET initially displays Web pages and WinForms in a Design view. But if you prefer Source view, you can set it to be the default view.

For Web pages:

Go to Tools | Options... | HTML Designer and select Source View.
Click OK button.

For WinForms:

Right-click on a WinForm in the Solution Explorer and then click Open With.... Open With dialog opens.
Choose CSharp Editor in the list and then click Set as Default button.
Click OK button.

Use DebuggerBrowsable attribute to clean up class view in a debugger

Sun, 02 Dec 2007 23:11:00 GMT

The DebuggerBrowsable attribute determines if and how a field or property is displayed in the debugger variable windows. Let's review the following code example:

    public class VehicleSeries
    {
        private string _name;
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
 
        private List<string> _vehicles = new List<string>();
        public List<string> Vehicles
        {
            get { return _vehicles; }
            set { _vehicles = value; }
        }
    }

The resulting display within the debugger is shown below:

Now lets remove duplicate information and show constituent vehicles by adding a few DebuggerBrowsable attributes:

    public class VehicleSeries
    {
        [DebuggerBrowsable(DebuggerBrowsableState.Never)]
        private string _name;
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
 
        [DebuggerBrowsable(DebuggerBrowsableState.Never)]
        private List<string> _vehicles = new List<string>();
        [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
        public List<string> Vehicles
        {
            get { return _vehicles; }
            set { _vehicles = value; }
        }
    }

This results in the following view in the debugger:

P.S. Also take a look at a tip "Use DebuggerDisplay attribute for a better debugger experience".

What is the difference between URL and URI?

Fri, 23 Nov 2007 21:46:00 GMT

A URL is the address of some resource on the web, which means that normally you type the address into a browser and you get something back. There are other type of resources than web pages, but that's the easiest conceptually. The browser goes out somewhere on the internet and accesses something.

A URI is just a unique string that uniquely identifies something, commonly a namespace. Sometimes they look like a URL that you could type into the address bar of your web browser, but it doesn't have to point to any physical resource on the web.

URI is the more generic term, and a URL is a particular type of URI in that a URL has to uniquely identify some resource on the web.

via Fedia.net

Don't generate unnecessary WinForm members for Label controls

Wed, 21 Nov 2007 20:54:00 GMT

To get rid of some auto-generated form level fields that point to a control that will never be referenced (for example, labels, panels, etc.), do the following:

In the Windows Forms Designer, select a control.
Set GenerateMember property for this control to false.

As a result a member of the form will not be generated for this control. It saves you 4 bytes per member and more importantly removes "clutter" from IntelliSense and any diagrams you autogenerate.

Simplify the usability of your generic methods with type parameter inference

Tue, 20 Nov 2007 17:54:00 GMT

When the parameter signature of a generic method includes a parameter that is of the same type as the type parameter for the method, it's not necessary to specify the type parameter when calling the method. Let's review an example:

    public class Class1
    {
        //both method type argument and parameter are of the same type
        public void SomeGenericMethod<T>(T sameAsTypeParameter)
        {
            ...
        }
    }
 
    public class Test
    {
        static void Main()
        {
            Class1 obj = new Class1();
            //It's not necessary to specify method type parameter
            //Instead of obj.SomeGenericMethod<int>(100) use
            obj.SomeGenericMethod(100);
        }
    }

As you can see in the example above, the syntax for calling generic method is identical to syntax of calling non-generic method. This ability is called generic type inference. To enable inference, the parameter signature of a generic method must include a parameter that is of the same type as the type parameter for the method.

Note: the compiler cannot infer the type based on the type of the returned value alone.

Two approaches to update database row if exists, insert if not

Sat, 17 Nov 2007 23:00:00 GMT

The biggest challenge with update/insert (so called upsert) is to minimize any kind of locks. Unfortunately there is no silver bullet for this yet. So let's review two the most commonly used methods:

1. Update, if @@ROWCOUNT = 0 then insert

    UPDATE Table1 SET Column1 = @newValue WHERE Id = @id
    IF @@ROWCOUNT = 0
    BEGIN
       INSERT INTO Table1 (Id, Column1) VALUES (@id, @newValue)
    END

This method is good if you know that in most of the cases a row will exist and update will be performed. Otherwise the second method should be used.

2. If row exists update, otherwise insert

    IF EXISTS(SELECT * FROM Table1 WHERE Id = @id)
    BEGIN
       UPDATE Table1 SET Column1 = @newValue WHERE Id = @id
    END
    ELSE
    BEGIN
       INSERT INTO Table1 (Id, Column1) VALUES (@id, @newValue)
    END

This one is good if you know that in most of the cases a row will not exist and insert will be performed. For such cases it executes SELECT statement followed by INSERT statement. That results in less expensive lock comparing to UPDATE + INSERT in previous method.

P.S. both methods should be used in transaction with isolation level Serializable.