ASP.Net Custom Control Render error

Question

I am trying to create a custom control and the render method is shown below.

I get an "Object reference not set to an instance of an object" error on the bulletList.RenderControl(Writer); line.

Any ideas?

    protected override void Render(HtmlTextWriter Writer)
    {
        if (TermSetList != null && TermSetList.Count > 0)
        {
            BulletedList bulletList = new BulletedList();
            bulletList.Click += new BulletedListEventHandler(BulletListItem_Click);
            bulletList.DisplayMode = BulletedListDisplayMode.LinkButton;
            bulletList.CssClass = "tabs";

            foreach (KeyValuePair<String, String> item in TermSetList)
            {
                ListItem listItem = new ListItem();

                listItem.Text = item.Key;
                listItem.Value = item.Value;

                bulletList.Items.Add(listItem);
            }

            if (!this.Page.IsPostBack)
            {
                bulletList.Items[0].Selected = true;
            }

            bulletList.RenderControl(Writer);

            base.Render(Writer);
        }
    }

Have you stepped through it yet? Is the Writer object properly instantiated when the Render method receives it? — Nathan Taylor
– Nathan Taylor, Commented May 27, 2011 at 16:20

Daniel · Accepted Answer · 2011-05-27 16:59:55Z

1

You generally do not want to add controls during render. How your currently doing this will ensure that your click handler never gets called.

My guess as to why you are getting the error is that the control has not been added to the controls collection.

My suggestion is to move the logic to an earlier event, perhaps onload, you would not need to override the Render method then.

answered May 27, 2011 at 16:59

Daniel

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