Following points are the main differences,
1) Client Data access:
ASP.NET 3.5:
There is no direct method to access data from client side.
Following are the methods available,
1) Pagemethods of script manager
2) ICallbackEventHandler interface
3) XMLHttphanlder component
ASP.NET 4.0:
In this framework there is an inbuilt feature for this.
Following are the methods to implement them.
1) Client data controls
2) Client templates
3) Client data context
i.e. we can access the data through client data view & data context objects from client side.
2) Setting Meta keyword and Meta description:
Meta keywords and description are really useful for getting listed in search engine.
ASP.NET 3.5: It has a feature to add Meta as a tag.
ASP.NET 4.0: Here we can add the keywords and description in Page directives itself as shown below.
< %@ Page Language="C#" CodeFile="Default.aspx.cs"
Inherits="_Default"
Keywords="Keyword1, Keyword2 ,etc"
Description="description" %>
3) Enableviewstate property for each control
ASP.NET 3.5: This property has two values "True" or "false"
ASP.NET 4.0: ViewStateMode property takes an enumeration that has three values:Enabled, Disabled, and Inherit.
Here inherit is the default value for child controls of a control.
4) Setting Client IDs
ASP.NET 3.5: Use ClientID property to find out the id which is dynamically generated
ASP.NET 4.0: The new ClientIDMode property is introduced to minimize the issues of earlier versions of ASP.NET.
It has following values.
AutoID - Same as ASP.NET 3.5
Static - There won't be any separate clientid generated at run time
Predictable-These are used particularly in datacontrols. Format is like clientIDrowsuffix with the clientid value
Inherit- This value specifies that a control's ID generation is the same as its parent.