Retrieving values from dynamically created controls Label in asp .net

Question

I have created Label controls dynamically on button click:

protected void createDynamicLabels_Click(object sender, EventArgs e)
{
    int n = 5;
    for (int i = 0; i < n; i++)
    {
        Label MyLabel = new Label();
        MyLabel.ID = "lb" + i.ToString();
        MyLabel.Text = "Labell: " + i.ToString();
        MyLabel.Style["Clear"] = "Both";
        MyLabel.Style["Float"] = "Left";
        MyLabel.Style["margin-left"] = "100px";

        Panel1.Controls.Add(MyLabel);
    }
}

When I tried to read back fro another button I see Label Control returned null

Label str = (Label)Panel1.FindControl("lb" + i.ToString());

not sure what went wrong here

protected void bReadDynValue_Click(object sender, EventArgs e)
{

  int n = 5;
    for (int i = 0; i < n; i++)
    {
        Label str = (Label)Panel1.FindControl("lb" + i.ToString());
        lbGetText.Text = str.Text;
    }


}

Faraz Ahmed · Accepted Answer · 2016-03-03 08:05:17Z

1

this is the issue of every time page load event. ASP.net fire every time page load event when any button is click.

suppose in this example..

protected void Page_Load(object sender, EventArgs e)
{

    if(!IsPostBack)
        createDynamicLabels();
}


private void createDynamicLabels()
    {
        int n = 5;
        for (int i = 0; i < n; i++)
        {
            Label MyLabel = new Label();
            MyLabel.ID = "lb" + i.ToString();
            MyLabel.Text = "Labell: " + i.ToString();
            MyLabel.Style["Clear"] = "Both";
            MyLabel.Style["Float"] = "Left";
            MyLabel.Style["margin-left"] = "100px";

            Panel1.Controls.Add(MyLabel);


        }
    }

protected void bReadDynValue_Click(object sender, EventArgs e)
{

    int n = 5;
    for (int i = 0; i < n; i++)
    {
        Label str = (Label)Panel1.FindControl("lb" + i.ToString());
        lbGetText.Text = str.Text;
    }


}

when Button trigger Page doesn't have any label because it is made on runtime. and Page doesn't find particular label. if you tried above code it is run properly.

 protected void Page_Load(object sender, EventArgs e)
{

        createDynamicLabels();
}


private void createDynamicLabels()
    {
        int n = 5;
        for (int i = 0; i < n; i++)
        {
            Label MyLabel = new Label();
            MyLabel.ID = "lb" + i.ToString();
            MyLabel.Text = "Labell: " + i.ToString();
            MyLabel.Style["Clear"] = "Both";
            MyLabel.Style["Float"] = "Left";
            MyLabel.Style["margin-left"] = "100px";

            Panel1.Controls.Add(MyLabel);


        }
    }

protected void bReadDynValue_Click(object sender, EventArgs e)
{

    int n = 5;
    for (int i = 0; i < n; i++)
    {
        Label str = (Label)Panel1.FindControl("lb" + i.ToString());
        lbGetText.Text = str.Text;
    }


}

in this Example code find label every time because every time it can make labels for this page.

answered Mar 3, 2016 at 8:05

Faraz Ahmed

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6 Comments

Ashok Over a year ago

Thanks, I wanted to do it 2 different buttons to generate dynamic controls and retrieve its values. But due to postback my idea of using 2 buttons not going to work. thanks again

Faraz Ahmed Over a year ago

@Ashok Why don't u use button event handler calling in else statement of (!isPostback).. it can work like this.. if you want to do with 2 buttons

Ashok Over a year ago

but Page_Load/postback called first, how do I know it is on that button click ?

Faraz Ahmed Over a year ago

here's the solution of your problem. stackoverflow.com/questions/18798940/…

Ashok Over a year ago

I tried that now on page_load I can see button control but Label ID is already null may be because postback is already happened !

|

mck · Accepted Answer · 2016-03-03 08:00:16Z

0

Dynamically created labels exists only until the next postback occurs. When you click on another button to retrieve their values a postback occurs and values become null.

For saving labels state after postback you have to use some hidden field.

answered Mar 3, 2016 at 8:00

mck

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1 Comment

Ashok Over a year ago

Thanks for the response

Glia · Accepted Answer · 2016-03-03 08:16:03Z

0

If the text / value of the labes does not change it is enough to generate them on every postback (as mck already mentioned). If you need to retrieve changes made on the client side, you should create the controls in the OnInit event instead of the PageLoad and use inputs / texboxes instead of labels.

Another option (which I would recommend) would be to use a asp:Repeater to generate the Labels.

answered Mar 3, 2016 at 8:16

Glia

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