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asp.net c# placeholder

Posted on 2010-11-22
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Last Modified: 2012-05-10
Q1: I have a list of placeholder name (.ascx) saved in database. like
hello1.ascx
hello2.ascx
hello3.ascx

I plan to use query to get list of placeholder into frontend placeholder object in aspx.
I have no problem to query them, but i don't know how to parse to the frontend placeholder.

Can you show me how? I would like to see in a function call because I will put it into App_Code folder.

Thanks,


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Question by:Webboy2008
13 Comments
 
LVL 20

Expert Comment

by:BuggyCoder
ID: 34190485
please explain in detail. can't make out anything out of your question
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Author Comment

by:Webboy2008
ID: 34190515
Table Name TblPlaceHolder

Column Name: PlaceHolder
hello1.ascx
hello2.ascx
hello3.ascx

Query Select PlaceHolder from TblPlaceHolder

Using Ado to get resultset from the query
Put all of the ascx to a single placeholder.
shown on the aspx

All languages using c#/asp.net

Hope this helps.


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LVL 1

Expert Comment

by:MLSmudde
ID: 34193322
I am assuming the user controls are files within your website.   To add a user control to an existing placeholder you add the control to the placeholder's contols collection.

UserControl myControl = Page.LoadControl("hello1.ascx");
TblPlaceHolder.Controls.Add(myControl);

To avoid viewstate issues,  you should add the controls in the page's OnInit method.
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LVL 29

Expert Comment

by:Kumaraswamy R
ID: 34194305
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LVL 18

Expert Comment

by:carlnorrbom
ID: 34195204
Hi,

I think you are after something like this:
    protected void Page_Load(object sender, EventArgs e)
    {
        //Get all the placeholder names from the database
        SqlConnection dbConn = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename=|DataDirectory|\\Database.mdf;Integrated Security=True;User Instance=True");
        SqlDataAdapter da = new SqlDataAdapter("SELECT PlaceHolder FROM tblPlaceHolder", dbConn);
        DataTable dtPlaceHolders = new DataTable();
        da.Fill(dtPlaceHolders);
        //Find the master placeholder in the page
        PlaceHolder phMain = (PlaceHolder)Page.FindControl("phMain");
        //Iterate over the database results to instantiate and load the user controls into the main placeholder
        foreach(DataRow row in dtPlaceHolders.Rows) {
            UserControl dbPlaceHolder = (UserControl)Page.LoadControl("~/" + row[0].ToString());
            phMain.Controls.Add(dbPlaceHolder);
        }
    }

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Above example assumes you have a placeholder in your page with ID="phMain" and the three user controls in the root of your app.

/Carl.
0
 

Author Comment

by:Webboy2008
ID: 34202019
error pointing to this code: phMain.Controls.Add(dbPlaceHolder);
Error Message: System.NullReferenceException: Object reference not set to an instance of an object.
When I use response.write to see the string.
It shows correct directory path.



using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Web.Configuration;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection DBSuretyCon = new SqlConnection(WebConfigurationManager.ConnectionStrings["SuretyDb"].ToString());
        SqlDataAdapter da = new SqlDataAdapter("SELECT AscxName FROM AdditionalInfoUI WHERE ClassCodeId =7 AND StatusId = 1",DBSuretyCon);

        DataTable dtPlaceHolders = new DataTable();
        da.Fill(dtPlaceHolders);
        //Find the master placeholder in the page
        PlaceHolder phMain = (PlaceHolder)Page.FindControl("phMain");
         //Iterate over the database results to instantiate and load the user controls into the main placeholder
        foreach (DataRow row in dtPlaceHolders.Rows)
        {
            UserControl dbPlaceHolder = (UserControl)Page.LoadControl("~/" + row[0].ToString());
            Response.Write("~/" + row[0].ToString() + "<br>");
            phMain.Controls.Add(dbPlaceHolder);

            
          }
        
    }   
}

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LVL 18

Expert Comment

by:carlnorrbom
ID: 34202928
Hi,

And you are sure you have the specific user control on that path? To me it sounds as if it can't find the usercontrol in question on the given path. The code works just fine for me on my end.

/Carl.
0
 

Author Comment

by:Webboy2008
ID: 34207703
it is a correct path
0
 
LVL 18

Expert Comment

by:carlnorrbom
ID: 34208228
Hi,

For Your reference and a proof of concept and validation of provided code, please see:

 carlnorrbom-373377.flv
0
 

Author Comment

by:Webboy2008
ID: 34208355
When I comment the following line of code. it is working.
PlaceHolder phMain = (PlaceHolder)Page.FindControl("phMain");
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Author Comment

by:Webboy2008
ID: 34208360
And I put PlaceHolder1.Controls.Add(dbPlaceHolder) instead in the ForEach Loop
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LVL 18

Accepted Solution

by:
carlnorrbom earned 500 total points
ID: 34208492
Hi,

Well naturally you need to replace the phMain ID with whatever is relevant in your solution, this is just a working sample.

/Carl.
0
 

Author Closing Comment

by:Webboy2008
ID: 34208506
It is working great. Thank you for your helps and efforts.

I have another post for 500pts if you want to try.

http://www.experts-exchange.com/Programming/Languages/.NET/ASP.NET/Q_26637414.html
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