Retrieve value of Dynamic controls in asp.net; Most important part for beginners programming

Object: our object is to access value of dynamic controls which are generated conditionally. For this, we will save viewstate of dynamic controls.
Suppose we have one dropdown and one button. When user selects “Generate” option, the Dynamic table will be generated. In each cell of table there will be textbox. User enters value in the textboxes and click on button then it will display all user entered values.

In aspx page

1. <form id="form1" runat="server">  
2.     <div>  
3.         <asp:Table ID="tbl" runat="server">  
4.         </asp:Table>  
5.     <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"   
6.         onselectedindexchanged="DropDownList1_SelectedIndexChanged">  
7.         <asp:ListItem>Select...</asp:ListItem>  
8.         <asp:ListItem>Generate</asp:ListItem>  
9.     </asp:DropDownList>  
10.         <asp:Button ID="btnSet" runat="server" Text="Button" onclick="btnSet_Click" /> </div>  
11.     </form>  

<form id="form1" runat="server">
    <div>
        <asp:Table ID="tbl" runat="server">
        </asp:Table>
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
        <asp:ListItem>Select...</asp:ListItem>
        <asp:ListItem>Generate</asp:ListItem>
    </asp:DropDownList>
        <asp:Button ID="btnSet" runat="server" Text="Button" onclick="btnSet_Click" /> </div>
    </form>

To create dynamic control:

view plainprint?

1. protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)  
2.     {  
3.         if (DropDownList1.SelectedIndex == 1)  
4.         {  
5.             CreateDynamicTable();  
6.         }  
7.     }  
8. private void CreateDynamicTable()  
9.     {  
10.          
11.         // Fetch the number of Rows and Columns for the table   
12.         // using the properties  
13.         int tblRows = 5;  
14.         int tblCols = 5;  
15.         // Now iterate through the table and add your controls   
16.         for (int i = 0; i < tblRows; i++)  
17.         {  
18.             TableRow tr = new TableRow();  
19.             for (int j = 0; j < tblCols; j++)  
20.             {  
21.                 TableCell tc = new TableCell();  
22.                 TextBox txtBox = new TextBox();  
23.                 txtBox.ID = "txt-" + i.ToString() + "-" + j.ToString();    
24.                 txtBox.Text = "RowNo:" + i + " " + "ColumnNo:" + " " + j;  
25.                 // Add the control to the TableCell  
26.                 tc.Controls.Add(txtBox);  
27.                 // Add the TableCell to the TableRow  
28.                 tr.Cells.Add(tc);  
29.                  
30.             }  
31.             // Add the TableRow to the Table  
32.             tbl.Rows.Add(tr);  
33.             tbl.EnableViewState = true;  
34.             ViewState["tbl"] = true;  
35.         }        
36.     }  

<br /><br />protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)<br />    {<br />        if (DropDownList1.SelectedIndex == 1)<br />        {<br />            CreateDynamicTable();<br />        }<br />    }<br />private void CreateDynamicTable()<br />    {<br />       <br />        // Fetch the number of Rows and Columns for the table <br />        // using the properties<br />        int tblRows = 5;<br />        int tblCols = 5;<br />        // Now iterate through the table and add your controls <br />        for (int i = 0; i < tblRows; i++)<br />        {<br />            TableRow tr = new TableRow();<br />            for (int j = 0; j < tblCols; j++)<br />            {<br />                TableCell tc = new TableCell();<br />                TextBox txtBox = new TextBox();<br />                txtBox.ID = "txt-" + i.ToString() + "-" + j.ToString();  <br />                txtBox.Text = "RowNo:" + i + " " + "ColumnNo:" + " " + j;<br />                // Add the control to the TableCell<br />                tc.Controls.Add(txtBox);<br />                // Add the TableCell to the TableRow<br />                tr.Cells.Add(tc);<br />               <br />            }<br />            // Add the TableRow to the Table<br />            tbl.Rows.Add(tr);<br />            tbl.EnableViewState = true;<br />            ViewState["tbl"] = true;<br />        }      <br />    }<br />

On Button click

view plainprint?

1. protected void btnSet_Click(object sender, EventArgs e)  
2.     {  
3.         foreach (TableRow tr in tbl.Controls )  
4.         {  
5.             foreach (TableCell tc in tr.Controls)  
6.             {  
7.   
8.                 if (tc.Controls[0] is TextBox)  
9.                 {   
10.                     Response.Write(((TextBox)tc.Controls[0]).Text);           
11.                 }  
12.             }  
13.             Response.Write("  
14. ");    
15.         }  
16.                 
17.     }  

<br /><br />protected void btnSet_Click(object sender, EventArgs e)<br />    {<br />        foreach (TableRow tr in tbl.Controls )<br />        {<br />            foreach (TableCell tc in tr.Controls)<br />            {<br /><br />                if (tc.Controls[0] is TextBox)<br />                { <br />                    Response.Write(((TextBox)tc.Controls[0]).Text);         <br />                }<br />            }<br />            Response.Write("<br/>");  <br />        }<br />              <br />    }<br />

This time No output because dynamic controls are lost in postback then what to do.
So we need to save dynamic controls value and generate dynamic controls again.we need to maintain viewstate.

view plainprint?

1. protected override object SaveViewState()  
2.     {  
3.         object[] newViewState = new object[2];  
4.   
5.         List txtValues = new List();  
6.                   
7.         foreach (TableRow row in tbl.Controls)  
8.         {  
9.             foreach (TableCell cell in row.Controls)  
10.             {  
11.                 if (cell.Controls[0] is TextBox)  
12.                 {  
13.                     txtValues.Add(((TextBox)cell.Controls[0]).Text);  
14.                 }  
15.             }  
16.         }  
17.   
18.         newViewState[0] = txtValues.ToArray();   
19.         newViewState[1] = base.SaveViewState();  
20.         return newViewState;  
21.     }  
22. protected override void LoadViewState(object savedState)  
23.     {  
24.         //if we can identify the custom view state as defined in the override for SaveViewState  
25.         if (savedState is object[] && ((object[])savedState).Length == 2 && ((object[])savedState)[0] is string[] )  
26.         {  
27.            object[] newViewState = (object[])savedState;  
28.             string[] txtValues = (string[])(newViewState[0]);  
29.             if (txtValues.Length > 0)  
30.             {   
31.                 //re-load tables  
32.                 CreateDynamicTable();  
33.                 int i = 0;  
34.                 foreach (TableRow row in tbl.Controls)  
35.                 {  
36.                     foreach (TableCell cell in row.Controls)  
37.                     {  
38.                         if (cell.Controls[0] is TextBox && i < txtValues.Length)  
39.                         {  
40.                             ((TextBox)cell.Controls[0]).Text = txtValues[i++].ToString();  
41.   
42.                         }  
43.                     }  
44.                 }  
45.             }  
46.             //load the ViewState normally  
47.             base.LoadViewState(newViewState[1]);  
48.         }  
49.         else  
50.         {  
51.             base.LoadViewState(savedState);  
52.         }  
53.     }  

<br /><br />protected override object SaveViewState()<br />    {<br />        object[] newViewState = new object[2];<br /><br />        List<string> txtValues = new List<string>();<br />                <br />        foreach (TableRow row in tbl.Controls)<br />        {<br />            foreach (TableCell cell in row.Controls)<br />            {<br />                if (cell.Controls[0] is TextBox)<br />                {<br />                    txtValues.Add(((TextBox)cell.Controls[0]).Text);<br />                }<br />            }<br />        }<br /><br />        newViewState[0] = txtValues.ToArray(); <br />        newViewState[1] = base.SaveViewState();<br />        return newViewState;<br />    }<br />protected override void LoadViewState(object savedState)<br />    {<br />        //if we can identify the custom view state as defined in the override for SaveViewState<br />        if (savedState is object[] && ((object[])savedState).Length == 2 && ((object[])savedState)[0] is string[] )<br />        {<br />           object[] newViewState = (object[])savedState;<br />            string[] txtValues = (string[])(newViewState[0]);<br />            if (txtValues.Length > 0)<br />            { <br />                //re-load tables<br />                CreateDynamicTable();<br />                int i = 0;<br />                foreach (TableRow row in tbl.Controls)<br />                {<br />                    foreach (TableCell cell in row.Controls)<br />                    {<br />                        if (cell.Controls[0] is TextBox && i < txtValues.Length)<br />                        {<br />                            ((TextBox)cell.Controls[0]).Text = txtValues[i++].ToString();<br /><br />                        }<br />                    }<br />                }<br />            }<br />            //load the ViewState normally<br />            base.LoadViewState(newViewState[1]);<br />        }<br />        else<br />        {<br />            base.LoadViewState(savedState);<br />        }<br />    }<br />

Hurray.. Now you can access dynamic control value on button click.