Set dropdown text selected from textbox value

In some cases we need to set dropdown list items exact text by matching the value entered in textbox. For that purpose we can use .keyup event in jQuery. In .keyup event simply take the value of textbox and assign that value to the value of dropdown. Once you set value it's corresponding text will be get displayed as selected.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <script src="Scripts/jquery-1.4.1.js" type="text/javascript"></script>
     <script src="Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>
    <title>Get dropdown value</title>
    <script type="text/javascript">
        $(document).ready(function () {
            $("#topics").keyup(function () {
                var value = $("#topics").val();
                if (value == "" || isNaN(value))
                    value = 0;
                $("#topics1").val(value);
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:TextBox runat="server" ID="topics"></asp:TextBox>
    <br/><br/>
      <asp:DropDownList ID="topics1" runat="server">
     <asp:ListItem Text="--Select--" Value="0"></asp:ListItem>
    <asp:ListItem Text="C#" Value="1"></asp:ListItem>
    <asp:ListItem Text="jQuery" Value="2"></asp:ListItem>
    <asp:ListItem Text="ASP.NET" Value="3"></asp:ListItem>
    </asp:DropDownList>
    </div>
    </form>
</body>
</html>

Note: You may need some additional validations if user enters data in textbox that does not match to the values in dropdown. Ex. I have just validated in above code if user enters characters other than number using IsNaN


jQuery templates

jQuery templates is a useful plugin developed by Microsofts's ASP.NET team in collaboration with jquery open source team. Templates helps you to manipulate the data at client side and display in browser. It is more useful to display the dataset that is fetched from database using client side Asynch Ajax call.

jQuery Template example

In order to use jQuery templates we either need to download "jquery.tmpl.js" plugin and add reference or we can also refer it from cdn.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
     <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
     <script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery.templates/beta1/jquery.tmpl.js"></script>
  <script type="text/javascript">

      $(document).ready(function () {
          debugger;
          var loc = window.location.href;
          $.ajax({
              type: 'POST',
              url: loc + "/GetBookList",
              data: "{}",
              contentType: "application/json; charset=utf-8"

          })
        .success(function (response) {
            debugger;
            $("#bookCollection").tmpl(response.d).appendTo(".book-container");
        })
        .error(function (response) {
            alert(response.d);
        });

      });
  </script>
</head>
<body>
    <form id="form1" runat="server">
    <div class="book-container">
    
    </div>
     <script id="bookCollection" type="text/x-jQuery-tmpl">
        <div>
           <h2>${Title}</h2>
            Author: ${Author}
            price: ${Price}
        </div>
    </script>
    </form>
</body>
</html>
Here in above code below script is template to which we are going to bind the data. <script id="bookCollection" type="text/x-jQuery-tmpl"> <div> <h2>${Title}</h2> Author: ${Author} price: ${Price} </div> </script> And by using $("#bookCollection").tmpl(response.d).appendTo(".book-container"); we actually bind the data to the template and append that template to some fixed html like div.


Below code is for reference to get data from code behind method:


 [WebMethod]
        public static List GetBookList()
        {

            return new List()
                       {
                           new Book {Title = "ASP.NET", Author = "Stephen", Price = 350.9},
                           new Book {Title = "WPF", Author = "Murli", Price = 400},
                           new Book {Title = "WCF", Author = "Avinash", Price = 350}
                       };
        }
Refer link to know how to make a ajax call to code behind.


Dynamic in C# 4.0

Dynamic type is introduced C# 4.0. As its name specifies type of the defined variable is decided dynamically at runtime. At compile time the variable that is declared as dynamic is assumed to be support any type or operation. As it does everything at runtime if code is not valid then errors are caught at runtime. Two major disadvantages of dynamic type are No compile time checking and No intelliSense support

Dynamic type example

Suppose we have class called SomeClass that have methods Method1() and Sum(intx, int y).
    public class SomeClass
    {
        public SomeClass()
        {
        }

        public void Method1()
        {
            //Do something
        }

        public int Sum(int x, int y)
        {
            return x + y;
        }
    }

and we are now trying to use the above class using dynamic type.
    public partial class DynamicType : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            dynamic someclass_dy = new SomeClass();
           
            someclass_dy.Method1();

            someclass_dy.Sum(10, 3);

            someclass_dy.SomeOtherMethod();
        }
     }

In above code we have defined dynamic type object of class SomeClass(). and now if you try to access methods from that class it will not show any method in intelliSense, you explicitly need to know the class methods and call them that is because dynamic type does not supports compile time checking. If you notice there is code line someclass_dy.SomeOtherMethod(); where SomeOtherMethod() does not exists in SomeClass() still it will not throw any compile time error, but it will throw runtime error.


Tuple in C# 4.0

Tuple is a new class introduced in C# 4.0. Tuple basically provides way to group the items of different data types. A static Tuple class provides 8 overloads of create method to create Tuple of size 1 to 8. Also using new keyword and nesting tuples you can create more sized Tuple. Now for example tuple created with 3 elements called 3-tuple or triple that can hold three elements of any type. So first element may be firstname that is string, second element may be phone number that is int and salary which is double may be the third element. And we can read those values using item property of tuple like for 3-tuple it will tuple.Item1, tuple.Item2 and tuple.Item3.

Tuple example 3-tuple

     var tuple3 = new Tuple("Johan", 1234567890, 56000.90);
     Console.WriteLine(tuple3.Item1);
     Console.WriteLine(tuple3.Item2);
     Console.WriteLine(tuple3.Item3);

In above example it will print
Output:
  Johan
  1234567890
  56000.90

Lazy loading C#. Lazy initialization.

C# 4.0 introduced new class Lazy which provided for Lazy initialization. Lazy instantiation here means object is not created until it is get used first time. Primary use of Lazy initialization is performance improvements, reduce program memory requirements.Lazy provides thread safe object initialization.

Lasy<T> example to load object lazily

public partial class LazyClass : System.Web.UI.Page 
{
 private Lazy<List<string>> lazyItems = null; 
 public LazyClass() 
 { 
   lazyItems = new Lazy<List<string>>(GetItems); 
 } 
 public List<string> GetItems() 
 {
      List<string> items = new List<string>(); 
      for (int i = 0; i < 10; i++) 
       { 
          items.Add(string.Format("Item {0}", i)); 
       } return items;
 }

 public List<string> GetItemValues { get { return lazyItems.Value; } } 
}

So in above example we have defined private Lazy<List<string>> lazyItems = null; and then in constructor we have delegate the call to GetItems method which will return list of items. But here it will not generate and return list until we call "lazyItems.Value".