Preserve value of textbox using View State in Asp.

问题:

I've a button and a textbox. I want a value to be entered in textbox and when I click on button the page will reload but the value should still be in the textbox. How can I do that. The following code doesn't work

namespace WebApplication2
{
    public partial class _Default : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                if (ViewState["value"] != null)
                {
                    TextBox1.Text = ViewState["value"].ToString();
                }
            }
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            ViewState["value"] = TextBox1.Text;
            Response.Redirect("default.aspx");
        }
    }
}

回答1:

Viewstate can retain the value only till when you are on the same page. You are redirecting to other page. So instead of using viewstate use session.

回答2:

Response.Redirect does what it says - redirects the request to a NEW page. ViewState won't get applied, ever. If you need a redirection, consider using session instead.

If you don't need a redirection, simply don't redirect and update only parts of the page that need to be updated.

回答3:

asp.net webform have already maintained the viewstate on page refresh . don't need any code for handle this operation .

See this : http://www.w3schools.com/aspnet/showaspx.asp?filename=demo_aspnetviewstate

referred from : http://www.w3schools.com/aspnet/aspnet_viewstate.asp

and see this discussion

回答4:

try this

namespace WebApplication2
{
   public partial class _Default : System.Web.UI.Page
    {

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            if (ViewState["value"] != null)
            {
                TextBox1.Text = Session["value"].ToString();
            }
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Session["value"] = TextBox1.Text;
        Response.Redirect("default.aspx");
    }
}

}

回答5:

Since you are redirecting to a new VIEW so VIEWSTATE will not be of any HELP. SO,Use Session

namespace WebApplication2
{
    public partial class _Default : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                if (Session["value"] != null)
                {
                    TextBox1.Text = Session["value"].ToString();
                }
            }
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            Session["value"] = TextBox1.Text;
            Response.Redirect("default.aspx");
        }
    }
}