unable to access public property value from a web user control to aspx

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I'm unable get a sting value which is the result of a "out parameter" of a function call which is result of DropDownList selectedIndexChange() event in ascx page, In debugging value is retriving from DB, when i'm tryin to access from host page, i'm getting null value.

all controls in this ascx are wrapped to updatePanel control,

C#

// Class of WebUserControl, Class name is TagQs
    public partial class TagQs : System.Web.UI.UserControl
    {
        public string ConString, Subject1, Subject2, Subject3, Subject4, Subject5, description;

        public string L1Subject
        {
            get { return Subject1;}
            set { Subject1 = Subject1 != null ? Subject1 : null; }
        }

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                // First time Page loading only
                //Subject1 = Subject2 = Subject3 = Subject4 = Subject5 = null;
            }
            else
            {
                // Partial page loading
                //Desc.Text = description;
            }

     }

// selectIndexChanged even of WUC (TagQs)        protected void DDLSubL1_SelectedIndexChanged(object sender, EventArgs e)
        {
                 // populate takes arguments and return result with a "out" parameter
            if (populate("PopulateL2Subjects", DDLSubL2, DDLSubL1, out Subject1))
            {
                DDLSubL2.Visible = true;
                this.L1Subject = Subject1;      // here working perfectly, till the postback
                ViewState["sub"] = Subject1;
            }
            else
            {
                DDLSubL2.Visible = false;
                DDLSubL2.Items.Clear();
                DDLSubL2.Items.Add("Select chapter");
            }
        }

///============================

// Code of HOST page
 public partial class Obj : System.Web.UI.Page
    {

       private string L1, L2, L3, L4, L5;
        protected void Page_Load(object sender, EventArgs e)
        {

            if (!Page.IsPostBack)
            {


            }
            else
            {

            }
        }

     }

// Here i'm accessing Property value
 //TagQ is the ID of WUC in host page   protected void BtnPreview_Click(object sender, EventArgs e)
        {

            L1 = TagQ.L1Subject;        // returns null always,
            L1 = (string)ViewState["sub"];
        }

Help me please!

Posted 15-Oct-12 8:38am

snsrkrishna

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3 solutions

Solution 2

A quick solution is to use viewstate to store and retrieve the property value, but i dont advise you use it without double checking if it is absolutely necessary.

C#

public string L1Subject
{
    get { return ViewState["Subject"]!=null?ViewState["Subject"].ToString():null;}
    set { ViewState["Subject"]=value; }
}

Also what you are doing inside the property doesnt make sense, you are setting the value of Subject1 by passing it as an OUT parameter to the function

populate("PopulateL2Subjects", DDLSubL2, DDLSubL1, out Subject1)

again you are using

this.L1Subject = Subject1;

through which you are setting the value of Subject1 again

set { Subject1 = Subject1 != null ? Subject1 : null; }

Also the logic you have used inside the set area of property is kinda funny i should say(sorry), you have checked if Subject1 is null and if null you set it with null else you set it again with its own value!!! that means 'your set block does nothing' and it wouldnt make any difference if you left your set block empty( set { } ) provided you are only doing what you are doing now inside it.

Feel free to correct me if i am wrong.

Posted 15-Oct-12 17:31pm

TheCoolCoder

Updated 15-Oct-12 19:04pm

v4

Comments

snsrkrishna 16-Oct-12 1:21am

thanks for the points (set{}), which you have stated. please refer my reply to "Marcus Kramer".

TheCoolCoder 16-Oct-12 2:05am

Your question ("OUT" value is having state only in SelectedIndexChanged event then how can i access the value out side of the block) answers itself , you have to maintain the out parameter's state manually. A simple public property of a usercontrol doesnt maintain its state across postbacks unless you make it do so. One method to maintain a property's state is what i have specified ofcourse at the expense of increased load to page by adding a viewstate variable. There are other workarounds like using a hiddenfield or implement LoadViewState, TrackViewState and SaveViewState for the control.Refer this

snsrkrishna 16-Oct-12 8:17am

thank you,

Solution 1

After postback you have to set the value of L1Subject from the client side object that contains the value. If you do not, L1Subject will remain null.
Remember that asp.net is stateless. By setting the value in the SelectedIndexChanged event, you are only setting it for the duration of the request to the server. The next postback will again start with a blank state.

Posted 15-Oct-12 9:15am

fjdiewornncalwe

Comments

snsrkrishna 16-Oct-12 1:18am

"After postback you have to set the value of L1Subject from the client side object that contains the value"

thanks for response, may i know how to set value "after postback", as you said the "OUT" value is having state only in SelectedIndexChanged event, then how can i access the value out side of the block, here i decalre subject1 as public variable

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snsrkrishna · Accepted Answer · 2012-10-16T04:31:00

Add a HiddenFiled in ascx and enable viewstate for the control, and set the value. For best practice, add a public property to ascx, and access property values from aspx page, by specifying "Classname.PropertyName".

.ASCX page

public string L1Subject
        {
            get { return Subject1 != null ? Subject1 : Subject1 = s1.Value; }
            set { Subject1 = value; }
        }

.ASPX page
L1 = Tagq.L1Subject.ToString();

* here s1 is a hidden field in ascx,
* and L1 is a string in aspx
* Tagq is class name of ascx

Thanking TheCoolCoder & Marcus Kramer again.