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Passing Values between ASP.NET Web Forms

Introduction

ASP.NET web forms provide excellent event driven programming model to developers. This does simplifies the overall design of your application but poses some problems of its own. For example, in traditional ASP you can easily pass values from one ASP page to another ASP page using POST. The same thing is not possible in ASP.NET if you want to stick to web form model (i.e. Server side form and control processing.). There are, however, some ways that can be used to overcome this situation. This article examines various possibilities to do the same. More specifically we will cover how to pass values using querystring, how to use session variables to do the same and finally how to use Server.Transfer method to do that.

Using Querystring

Querystring is a day old mechanism to pass values across pages. The main advantage of this method is it is very simple. However, disadvantages are the values are visible in the browser address bar and you can not pass objects this way. This method is best suited when you want to pass small number of values that need not be secured from others. In order to implement this method you will follow these steps:
  • Create the web form with controls
  • Provide some button or link button that posts the form back
  • In the click event of the button create a string that holds URL for another
  • Add control values to this URL as querystring parameters
  • Response.Redirect to another form with this URL
Following code snippet shows how it works:
Source Web Form
private void Button1_Click
(object sender, System.EventArgs e)
{
	string url;
	url="anotherwebform.aspx?name=" + 
		TextBox1.Text + "&email=" + 
		TextBox2.Text;
	Response.Redirect(url);
}
Destination Web Form
private void Page_Load
(object sender, System.EventArgs e)
{
	Label1.Text=Request.QueryString["name"];
	Label2.Text=Request.QueryString["email"];
}

Using Session variables

This is yet another way to pass values across pages. Here you store control values in session variables and access them in another web form. However, as you know storing too much data in session can be an overhead on the server. So, you should use this method with care. Also, it requires some kind of clean up action from your side so that unwanted session variables are removed. The typical sequence of steps will be as follows:
  • Create the web form with controls
  • Provide some button or link button that posts the form back
  • In the click event of the button add session variables and set them to control values
  • Response.Redirect to another form
  • In that form access Session variables and remove them if necessary
Following code shows this in action:
Source Web Form
private void Button1_Click
(object sender, System.EventArgs e)
{
	//textbox1 and textbox2 are webform
	//controls
	Session["name"]=TextBox1.Text;
	Session["email"]=TextBox2.Text;
	Server.Transfer("anotherwebform.aspx");
}
Destination Web Form
private void Page_Load
(object sender, System.EventArgs e)
{
	Label1.Text=Session["name"].ToString();
	Label2.Text=Session["email"].ToString();
	Session.Remove("name");
	Session.Remove("email");
}

Using Server.Transfer

This is somewhat complex but sophisticated method of passing values across pages. Here you expose the values you want to access in other pages as properties of the page class. This methods require you to code extra properties that you can access in another web form. However, the efforts are worth considering. Overall this method is much cleaner and object oriented than earlier methods. The entire process works as follows:
  • Create the web form with controls
  • Create property Get procedures that will return control values
  • Provide some button or link button that posts the form back
  • In the button click event handler call Server.Transfer method that will transfer execution to the specified form
  • In the second form you can get a reference to the first form instance by using Context.Handler property. Then you will use the get properties we created to access the control values.
The code to accomplish this is somewhat complex and is shown below:
Source Web Form
Add following properties to the web form:
public string Name
{
	get
	{
		return TextBox1.Text;
	}
}

public string EMail
{
	get
	{
		return TextBox2.Text;
	}
}
Now, call Server.Transfer.
private void Button1_Click
(object sender, System.EventArgs e)
{
	Server.Transfer("anotherwebform.aspx");
}
Destination Web Form
private void Page_Load
(object sender, System.EventArgs e)
{
	//create instance of source web form
	WebForm1 wf1;
	//get reference to current handler instance
	wf1=(WebForm1)Context.Handler;
	Label1.Text=wf1.Name;
	Label2.Text=wf1.EMail;
}

Summary

In this article we saw various ways to pass data between two ASP.NET web forms. The three methods viz. Querystring, Session and Server.Transfer provide ways to pass our values across pages. We also saw pros and cons of each method.

I hope you must have found this article useful. See you soon. Till then keep coding!


Bipin Joshi is the founder of BinaryIntellect Consulting and conducts professional training programs on ASP.NET in Thane. He is a published author and has authored or co-authored books for Apress and Wrox press. To know more about him click here. To know more about his training programs go here.

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Tags : ASP.NET Web Forms
Posted On : 19 Apr 2002
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