Question

Retreiving a Usercontrol property on Postback

Asked by: gjok

Hi.
asp.net 2.0 / c#

I have a webform with a thumbnail usercontrol. The usercontrol has an int property called ImageID.
When the page loads the ImageID is assigned, but when I do a postback, the property is set to zero !

How do I get it to remember the properties value on postback (like other webcontrols do, such as textboxes or checkboxes)

// Usercontrol code
public int ImageID
{
  get { return _imgId; }
  set { _imgId = value; }
}
 
 
// Webform Code
protected void Page_Load(object sender, EventArgs e)
{
  if (!IsPostBack)
    LoadProfile();
}
 
protected void LoadStripProfile()
{
  Portfolio pf = Portfolio.Retrieve(ArtistID);
  MyThumbnail1.ImageID = pf.StripThumb1;
  MyThumbnail2.ImageID = pf.StripThumb2;
  MyThumbnail3.ImageID = pf.StripThumb3;
}
 
protected void btnSave_Click(object sender, EventArgs e)
{
  if (MyThumbnail2.ImageID == 0)
    lbl.Text="No ImageID";
  else
    lbl.Text="ImageID is " + MyThumbnail2.ImageID;
}

                                  
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Asked On
2008-04-04 at 10:04:12ID23296667
Tags

c# asp.net

Topics

Programming for ASP.NET

,

C# Programming Language

,

.NET Framework 2.x

Participating Experts
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Answers

 

by: Nash2334Posted on 2008-04-04 at 10:22:59ID: 21283820

Remove the if (!IsPostBack) check.

protected void Page_Load(object sender, EventArgs e)
{
    LoadProfile();
}

 

by: gjokPosted on 2008-04-05 at 09:49:32ID: 21288744

The usercontrol is a kind of thumbnail which you can click to assign a new image.

There are other elements on the form such as textboxes, etc, so if I remove the (!IsPostBack) check then my LoadProfile function will overwrite the modified textbox values with the original data.

So, unfortunately I need the postback to validate the textboxes.

 

by: Nash2334Posted on 2008-04-05 at 12:33:46ID: 21289313

Then set a session variable, check to see if it exists and if so assign the ID:

protected void Page_Load(object sender, EventArgs e)
{
  if (!IsPostBack)
  {
    LoadProfile();
    Session("ImageID") = UserControl.ImageID;
  }
  else
  {
    int _imageID = (int)Session("ImageID");
   
    if (_imageID != null)
      UserControl.ImageID = _imageID;
  }
}

 

by: gjokPosted on 2008-04-06 at 01:01:58ID: 21291086

That is one option - but I have 20 of these controls on the page.

What I dont understand is that a textbox, checkbox, dropdown, etc ALL remember their values on postback, so why doesnt my user control?

There must be something I need to do to the usercontrol to make it have a viewstate...

 

by: gjokPosted on 2008-04-06 at 01:16:18ID: 21291112

I have it!  (see snippet)

Its all to do with the ViewState. I found this article on MSDN:
http://msdn2.microsoft.com/en-us/library/ms972975.aspx#usercontrols_topic7

The viewstate must be set in the usercontrol' s property.

// Adadpted from eample on MSDN.
 
  public int ImageID
  {
    //get { return _imgId; }
    //set { _imgId = value; }
 
    get
    {
      object o = ViewState["ImageID"];
      if (o == null)
        return 0;   // return a default value
      else
        return (int)o;
    }
    set
    {
      _imgId = value;
      ViewState["ImageID"] = value;
    }
  }

                                              
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