Make your site run only in ONE Browser window(single instance)!

djsolid — Sun, 15 Nov 2009 10:49:00 GMT

While a was at Teched2009 and watching Tim Heuer presenting Silverlight 3 I noticed a new cool feature named Local Messaging!

When I saw this new feature, a crazy idea crossed my mind. Could this be used in order to allow the user to open my website in only one browser window?

The answer is yes! But not the way I first thought. Here is how (code in MainPage.xaml.cs):

string _localName = "SL App";
bool _Close = false;

public MainPage()
{
   InitializeComponent();

   Loaded += new RoutedEventHandler(MainPage_Loaded);
   try
   {
       LocalMessageReceiver incomingMessage = new LocalMessageReceiver(_localName);
       //Start listening
       incomingMessage.Listen();
   }
   catch (ListenFailedException)
   {
       _Close = true;
   }            
}

protected void MainPage_Loaded(object sender, RoutedEventArgs e)
{
   if (_Close)
   {
       HtmlPage.Window.SetProperty("location", "/InfoMessage.aspx");
   }
   else
   {
       LocalMessageSender msgSender = new LocalMessageSender(_localName);
       msgSender.SendAsync("New instance loaded");
   }
}

Loading Default.aspx

Clicking on the first link

Then on the second link

Those are the files in the solution

That’s an exception driven solution but works for me! :)

This works also across different browsers but if you want you can changed to allow one instance per browser.

Here are the solution files.

Enjoy!

Set default value for Properties

djsolid — Thu, 18 Sep 2008 09:25:00 GMT

Many times I needed to set a default value for a property.

For example at the property below

public string Property1 {get; set;}

I wanted a default value "Value1". The only way was to create a private field or to set it in code like Property1 = "Value1" somewhere.

What if I wanted to do this for all my properties ?

For this case i decided to create a custom attribute which does that thing. Takes a value and if the value of the current property is null sets it to the given value.

To be more specific let's begin with the custom attribute class:

 [global::System.AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
    sealed class DefaultValueAttribute : Attribute
    {
        readonly object defaultValue;
        readonly Type valueType;

        public DefaultValueAttribute(object defaultValue, Type valueType)
        {
            this.valueType = valueType;
            this.defaultValue = Convert.ChangeType(defaultValue, valueType);
        }
        public Type ValueType { get { return valueType; } }
        public object DefaultValue
        {
            get { return defaultValue; }
        }
    }

Then we have a helper class with an extension method :

public static class DefaultValueAttributeHelper
    {
        public static void SetDefaultValues(this object obj)
        {
            Type t = obj.GetType();
            foreach (var item in t.GetProperties())
            {
                foreach (var attr in item.GetCustomAttributes(typeof(DefaultValueAttribute), true))
                {
                    DefaultValueAttribute val = ((DefaultValueAttribute)attr);
                    if (item.GetValue(obj, null) == null ||
                        ((item.GetValue(obj, null).ToString() == "0") && 
                                       (val.ValueType != typeof(string))))
                        item.SetValue(obj, val.DefaultValue, null);
                }
            }

        }
    }

And finally how this can be used for example at an ASP.NET Page:

public partial class UserDetails : System.Web.UI.Page
    {
        public UserDetails()
        {
            this.SetDefaultValues();
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            Response.Write(StringProp + "<br>" + IntProp + "<br>" + (DoubleProp + 1));
        }

        [DefaultValueAttribute("6.11354", typeof(double))]
        public double DoubleProp { get; set; }

        [DefaultValueAttribute("6", typeof(int))]
        public int IntProp { get; set; }

        [DefaultValueAttribute("String1", typeof(string))]
        public string StringProp { get; set; }


    }

Well that's all ... This is really simple. Next step is to create an interface so the above attirbute can be used with custom objects.

If anyone has any improvements please let me know!

Web Dev And Stuff : C#

Make your site run only in ONE Browser window(single instance)!

Set default value for Properties