Call a Function on Dynamically Generated ASP:Button in ASP.NET c#

The problem here is that you're generating the code to run on the client-side, but including scripts and tags designed to be run through the asp.net processor:

objSBuilder.Append("<div class='control-group'><asp:Button Text='AddtoCart' runat='server' id='" + ((DataRow)row)["PlanId"].ToString() + "' class='btn btn-small btn-success' onclick='AddPlanToCart();' /></div>");

which produces HTML including [slightly reformatted]:

<div class='control-group'>
    <asp:Button ... onclick='AddPlanToCart();' />
</div>

instead of the <button> control that you're obviously expecting.

Fixing this to work in the manner its written in would be a significant amount of work. Instead, I'd strongly recommend rewriting it to use an <asp:repeater> control instead.

Your onclick is attempting to call a javascript function AddPlanToCart(). You have a couple of options. Here's 2:

1) Create a javascript that does a postback with a specific query string. Check for the query string in page_load, if it exists then call the function.

2) Create an actual dynamic control. It should be created in Page_init if you want to track it's viewstate, not Page_load. Then Add an event handler for the button.

Button b2 = new Button();
b2.Text = "Add To Cart";
b2.Click += new EventHandler(AddPlanToCart);

When creating the button, you can also bind the click event, to a delegate like the following:

Button btn = new Button();
btn.Text = "Button text";
btn.AutoSize = true;
btn.Location = new Point(y, 0);
btn.Click += delegate(object sender, EventArgs e)
{
    solution.Invoke(); 
}; 

In this case I am passing an Action<>, as a parameter within the method. When you click on the button, the delegate would be triggered. For instance, this button would be created, and when clicked, a messagebox would show:

Button btn = new Button();
btn.Text = "Button text";
btn.AutoSize = true;
btn.Location = new Point(y, 0);
btn.Click += delegate(object sender, EventArgs e)
{
    MessageBox.Show("Clicked!");
}; 

For your scenario, try something within these lines:

int counter = 0;

// Display each item of ArrayList
foreach (Object row in myArrayList)
{
    Control ctrl = new Control();

    Label lbl = new Label();
    lbl.Text = "Label " + counter.ToString();

    Button btn = new Button();
    btn.Text = "Button text " + counter.ToString(); 
    btn.Click += delegate(object sender, EventArgs e)
    {
        Response.Write("<script>alert('Message for button " + counter.ToString() + "');</script>");
    }; 

    ctrl.Controls.Add(lbl);
    ctrl.Controls.Add(btn);

    counter++; 

    PlanContent.Controls.Add(ctrl);
}