State Management

The variables get forgotten while the page reloads. You can save their values with the following state management techniques:

On server side:

· Application variable

· Session variable

· Profiles

On client side:

· Cookies

· Hidden Fields

· Query Strings

· State View

· Control State

Session and Application variables

Default.aspx

protected void Page_Load(object sender, EventArgs e)

{

string s = Application["zm1"].ToString();

int z = Convert.ToInt32(s);

if (!IsPostBack)

z++;

s = Convert.ToString(z);

Application["zm1"] = s;

TextBox1.Text = Application["zm1"].ToString();

string s2 = Session["zm2"].ToString();

int z2 = Convert.ToInt32(s2);

z2++;

s2 = Convert.ToString(z2);

Session["zm2"] = s2;

TextBox2.Text = Session["zm2"].ToString();

}

Global.asax

<%@ Application Language="C#" %>

void Application_Start(object sender, EventArgs e)

{

// Code that runs on application startup

Application.Add("zm1", 1);

}

void Application_End(object sender, EventArgs e)

{

// Code that runs on application shutdown

}

void Application_Error(object sender, EventArgs e)

{

// Code that runs when an unhandled error occurs

}

void Session_Start(object sender, EventArgs e)

{

// Code that runs when a new session is started

Session.Add("zm2", 1);

}

void Session_End(object sender, EventArgs e)

{

// Code that runs when a session ends.

// Note: The Session_End event is raised only when the sessionstate mode

// is set to InProc in the Web.config file. If session mode is set to StateServer

// or SQLServer, the event is not raised.

}

</script>

Profiles

Add to web.config under the <system.web> section:

</properties>

</profile>

In Default.aspx.cs:

public partial class _Default : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

// Check if the user's name is defined, and greet him

if (Profile.UserName.Length > 0)

Label1.Text = "Welcome, " + Profile.UserName + "! ";

// Define the first visit time if necessary

if (Profile.FirstVisit.Year < 1900)

Profile.FirstVisit = DateTime.Now;

}

protected void Button1_Click(object sender, EventArgs e)

{

Profile.UserName = TextBox1.Text;

}

Cookies

protected void Page_Load(object sender, EventArgs e)

{

int clicks;

if (Request.Cookies["clicks"] != null)

clicks = Convert.ToInt32(Request.Cookies["clicks"].Value) + 1;

else

clicks = 1;

// Define the cookie for the next visit

Response.Cookies["clicks"].Value = clicks.ToString();

TextBox1.Text = clicks.ToString();
}

protected void Button8_Click(object sender, EventArgs e)

{

HttpCookie cx = new HttpCookie("pies", "szarik");

cx.Expires = DateTime.Now.AddDays(7);

Response.Cookies.Add(cx);

Response.Cookies["kot"].Value = "mruczek";

Response.Cookies["kot"].Expires = DateTime.Now.AddDays(7);

}

protected void Button9_Click(object sender, EventArgs e)

{

string s = Request.Cookies["kot"].Value;

Label1.Text = s;

}

You typically can store up to 20 cookies per site (depending on browser), and each cookie can be up to 4 KB in length. To work-around is to store multiple values in a cookie:

Response.Cookies["YourDog "]["LastVisit"].Value = DateTime.Now.ToString();

Response.Cookies["YourDog "]["name"].Value = "chic";

Response.Cookies["YourDog "]["color"].Value = "black";

Response.Cookies["YourDog "].Expires = DateTime.Now.AddDays(14);

Hidden Fields

protected void Page_Load(object sender, EventArgs e)

{

int clicks1;

int.TryParse(HiddenField1.Value, out clicks1);

clicks1++;

HiddenField1.Value = clicks1.ToString();

Label1.Text = "HiddenField clicks: " + HiddenField1.Value;
}

Query Strings

protected void Page_Load(object sender, EventArgs e)

{

int queryClicks;

if (Request.QueryString["clicks"] != null)

queryClicks = int.Parse(Request.QueryString["clicks"]) + 1;

else

queryClicks = 1;

// Define the query string in the hyperlink

HyperLink1.NavigateUrl += "?clicks=" + queryClicks.ToString();

TextBox2.Text = queryClicks.ToString();
}

Switching between pages loses all Hidden Field information but Cookies are preserved.

ViewState

If you click a button to submit an ASP.NET page, the page retains all its values (e.g. textboxes) and settings after it reappears. This is implemented by a client-side state management technique called ViewState. The code sample shows how view state adds data as a hidden field within a Web page’s HTML (in the same form values of other fields are preserved):

View state is enabled by default for every control. To make the page reload faster, you can disable it by setting the EnableViewState property for each Web control to False.

You can also add and retrieve custom values with ViewState, as shown below:

public partial class _Default : System.Web.UI.Page

{

[Serializable]

public class dog

{

public int size;

public string name;

public dog(int size, string name)

{

this.size = size;

this.name = name;

}

dog dog1;

protected void Page_Load(object sender, EventArgs e)

{

dog1 = new dog(15, "chic");

if (ViewState["YourDog"] != null)

{

dog1 = (dog)ViewState["YourDog"];

dog1.size++;

dog1.name += dog1.name.Substring(3, 1);

}

else

{

ViewState.Add("YourDog",dog1);

}

ViewState["YourDog"] = dog1;

TextBox1.Text = dog1.size.ToString();

TextBox2.Text = dog1.name;

}

protected void Button1_Click(object sender, EventArgs e)

{

}

That’s how much you can put into a (very long) View State:

protected void Button2_Click(object sender, EventArgs e)

{

VS []vs = new VS[100];

List<VS> A = new List<VS>();

for (int i = 0; i < 100; i++)

{

vs[i] = new VS();

vs[i].vsName = "Ala Ma Asa nr " + i.ToString();

vs[i].vsValue = 10*i;

A.Add(vs[i]);

}

ViewState.Add("A", A);

}

protected void Button3_Click(object sender, EventArgs e)

{

List<VS> A = new List<VS>();

A = (List<VS>) ViewState["A"];

foreach (VS v in A)

{

Label1.Text += v.vsName + " " + v.vsValue.ToString() + " ";

}