Any alternate way to avoid null value return in asp.net server control

Question

I created a server control and test.aspx Code is shown below .

When dll is loaded , RenderContents() function gets called.
Control transfer to DataSource property , but ViewState["DataSource"] returns null .

To avoid it , I initialized ViewState["DataSource"] using -

ViewState["DataSource"] = _Pages_dummy;

My Question is - if i do not want to use initialization , is there any alternate way so that ViewState["DataSource"] will not return null value "?

=================================== ===============================================

using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace ServerControl2
{
    [DefaultProperty("Text")]
    [ToolboxData("<{0}:ServerControl1 runat=server></{0}:ServerControl1>")]
    public class ServerControl1 : WebControl
    {
        private string[,] _Pages_dummy= { {"1","2","3","4"} ,  {"11","22","33","44"}};

        public ServerControl1() 
        {
           ViewState["DataSource"] = _Pages_dummy; 
           // if user do not initialize viewstate , we use dummmey array .
        }

        public ServerControl1(string[,] pages)        
        {
            ViewState["DataSource"] = pages;  
           // user must initialize viewstate .
        }

        [Bindable(true)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
         public  string[,]  DataSource
        {
            get
            {
                return (string[,])ViewState["DataSource"];
            }
            set
            {
                ViewState["DataSource"] = value;
            }
        }    
        [Bindable(true)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
        protected override HtmlTextWriterTag TagKey
        {
            get
            {
                return HtmlTextWriterTag.Div;
            }
        }

        protected override void RenderContents(HtmlTextWriter output)
        {
            output.WriteBeginTag("div");

            if (DataSource != null)
            {
                    for (int i = 0; i < DataSource.GetLength(0); i++)
                    {
                       for (int j = 0; j < DataSource.GetLength(1); j++)
                       {

                       }
                   }
            }    
        } // RenderContents     
    }// class
}// namespace

test.aspx.cs

         ServerControl2.ServerControl1 n1 = new ServerControl2.ServerControl1();                     
          n1.DataSource[0,0] = "hjkhjk";
          n1.DataSource[0,1] = "jkljk";
          n1.DataSource[0,2] = "hjk";
          n1.DataSource[0,3] = "fjgfjhhgj";   
          Response.Write(n1.DataSource[0,0]);
          Response.Write(n1.DataSource[0,1]);
          Response.Write(n1.DataSource[0,2]);
          Response.Write(n1.DataSource[0,3]);

I'm not really clear on why you want this, but if you want ViewState["DataSource"] to always have a value, you would have to initialize it to *something*. It starts out being empty. — Ann L., Mar 07 '13 at 18:56
If you don't put a value in the viewstate variable, and you try to retrieve it, what could you possibly expect to retrieve other than null? — dave823, Mar 07 '13 at 19:06
See inside default contructor . Suppose I comment // ViewState["DataSource"] = _Pages_dummy; What I want is - ViewState["DataSource"] should not return null . Is it possible? — Bhushan Mahajan, Mar 07 '13 at 19:07
When dll is loaded , RenderContents() function gets called internally . Hence it is not possible to initialize by calling default constructor . Did You get my point? — Bhushan Mahajan, Mar 07 '13 at 19:09
Not possible. It doesn't really make sense. If you never set it to something, it will always be null, unless you do something like in Ceres' answer, where you initialize it in the property definition — dave823, Mar 07 '13 at 19:10

score 0 · Accepted Answer · answered Mar 07 '13 at 19:07

0

Check if the viewstate is null in the Datasource property. As long as you use the property instead of Viewstate("Datasource") directly, you should be fine.

[Bindable(true)]
[Category("Appearance")]
[DefaultValue("")]
[Localizable(true)]
 public  string[,]  DataSource
{
    get
    {
        string[,] value = (string[,])ViewState["DataSource"];
        if (value == null) {
            return __Pages_dummy

        }
        return value ;
    }
    set
    {
        ViewState["DataSource"] = value;
    }
}

answered Mar 07 '13 at 19:07

Ceres

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I tried string[,] value = (string[,])ViewState["DataSource"]; if (value == null) { return _Pages_dummy; } return value ; It is working fine. But how will i come know what should be size of _Pages_dummy. It may differ in various scenarios . I can not guess _Pages_dummy size . – Bhushan Mahajan Mar 07 '13 at 19:22
string[,] value = (string[,])ViewState["DataSource"]; if (value == null) { return null; } return value ; Now It is working . Thanks Ceres. – Bhushan Mahajan Mar 07 '13 at 20:00

Any alternate way to avoid null value return in asp.net server control

1 Answers1