Is there a reason why author called DataBind manually?

carewithl · October 6th, 2009, 01:29 PM

Hi,

1)
page 246 - Inside GridView.RowDeleted event handler author manually calls gvwCategories.DataBind
page 255 – Inside Page_Load author manually calls gvwArticles.DataBind
page 256 – inside ddlCategories_SelectedIndexChanged() author manually calls gvwArticles.DataBind

In all of the above cases author manually called DataBind instead of letting Asp.Net perform automatic data binding. I’ve omitted the above code from the application in order to see if Asp.Net would perform the data binding automatically, which it did.

a) Now since Asp.Net did perform automatic data binding, is there some other reason why author decided to manually call DataBind in the above methods?

2) page 247 – If user presses Cancel button, then insidedvwCategory_ItemCommand() author manually calls gvwCategories.DataBind().

I don’t see a point in doing that, since user canceled the operation ( by pressing Cancel button ) and thus DB wasn’t changed in any way. Thus I don’t think there is any point in rebinding gvwCategories inside dvwCategory_ItemCommand?! Correct?

thanx

Imar · October 6th, 2009, 04:39 PM

Does it really bind? Or reconstruct the data from View State?

Do you actually see the deleted item disappear from the list? That's typically the reason to manually call DataBind: to force a refresh of the data.

Imar

carewithl · October 7th, 2009, 08:36 PM

Quote:

Originally Posted by Imar

Does it really bind? Or reconstruct the data from View State?

Do you actually see the deleted item disappear from the list? That's typically the reason to manually call DataBind: to force a refresh of the data.

Imar

Yes Iâm sure. Hereâs how Iâve figured out that gvwCategories.DataBind statement (inside gvwCategories_RowDeleted event handler) isn't really necessary:

1 â first I've delete gvwCategories.DataBind(); statement ( inside gvwCategories_RowDeleted event handler )

Code:

      protected void gvwCategories_RowDeleted(object sender, GridViewDeletedEventArgs e)
        {
           gvwCategories.SelectedIndex = -1;
          // gvwCategories.DataBind();
           dvwCategory.ChangeMode(DetailsViewMode.Insert);
        }

2 â I then browsed to ManageCategories.aspx page, which displayed all the available categories

3 â I then opened Sql server and manually added a new entry to tbh_Categories table ( in other words, Iâve created a new category and named it Y ). Now if Asp.Net does perform automatic data binding when some category is deleted, then gvwCategories will also display new category Y

4 â Iâve then deleted âBeer-related articlesâ category ( by pressing Delete button)

5 â after a postback, gvwCategories also displayed category Y

Thus, if Asp.Net didnât perform automatic binding, but instead reconstructed the data from viewstate, then gvwCategories wouldnât also display category Y.

BTW - I did similar checks for code on pages 255 and 256

Imar · October 8th, 2009, 04:34 AM

Do you disable ViewState somewhere? On the control, the page or in Web.config?

Imar

carewithl · October 8th, 2009, 11:07 AM

Quote:

Originally Posted by Imar

Do you disable ViewState somewhere? On the control, the page or in Web.config?

Imar

No. I've only omitted the gvwCategories.DataBind; statement, but left all of author's other code as it was ( and as far as i can tell, author hasn't disabled the viewstate )

Lee Dumond · October 8th, 2009, 06:13 PM

Good catch. In these cases, the call to DataBind is not actually needed.

This is because whenever the page is created, or recreated after a postback, the following occurs:

The ConfirmInitState method of the Gridview is called.
The DataSourceID property (obtained from the declarative markup) is set to the ID of the ObjectDataSource.
This then causes the OnDataPropertyChanged method to be called.
The OnDataPropertyChanged method sets the RequiresDataBindingProperty to true.
This then forces the DataBind method to be called before the control is rendered.

This is true for any control that inherits from BaseDataBoundControl.

carewithl · October 9th, 2009, 06:58 PM

alrighty, thank you for your help