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October 17, 2006

Adding Multiple Checkbox Items to Datagrid for Selecting, Confirming and Deleting the Selected Data

As a .Net developer, we know the importance of the datagrid in web applications. In ASP days, we used to write the code to generate the data in table format and add bit of complex code for paging and sorting of the data.

To avoid this much code and to make developer HAPPY, Microsoft came up with nice and cool control called Datagrid with minmum code and have the features like paging and sorting.

But some times we have to select the data from the datagrid then we process the data for modifying or deleting the data. So for that generally we add checkbox control to the for each row of the datagrid, so based on that we will select the checkbox for further processing of the data.

Here i am explaining the steps to add the checkbox to the datagrid and little of coding to select data for further processing.

In this article, we will examine how to create a fully functional DataGrid with all the features like seelctign the data for further processing. As an added bonus we'll be performing all of our data tasks strictly utilizing Microsoft's new Data Access Application Block or DAAB v2. To any who may feel a little behind with DAAB, have no fear, everything here can still be accomplished with pre-DAAB data objects as the only difference here is the data access part of it. Trust me there is a huge difference between the two, for one DAAB enable you to write about 75% less code that you would normally need when compared with regular ADO.NET!

So, before we begin, download the DAAB dll from the above link, install it, and copy it into you application's bin folder and you're ready to go. Also, be sure and take a peek at the DAAB documentation that came with your installation for an overview and any questions you may have.

Ok, let's get to it then.

Our fully-featured DataGrid

Selecting & deleting multiple items will definitely be set up quite differently than any other type of .NET DataGrid deleting you probably have seen. However, we'll still follow the same logical flow of deletion, and we'll still confirm any delete actions about to take place after we have selected all our items. Much of the magic in making this work is really going to come from client-side JavaScript, that is ultimately responsible for wiring up our main "select all" checkbox to handle the selecting and deselecting of our checkboxes. Also, included is our server-side delete method that erases our data, and a DataGrid refresher method to rebind our DataGrid after we have completed our data deletion.

Have a look at Figure 1 to get an idea of what your DataGrid will look like:

Figure 1

Here is the code to set up our DataGrid:

<form runat="server" ID="Form1">
<h3>Selecting, Confirming & Deleting Multiple Checkbox Items In A DataGrid </h3>
<ASP:DataGrid id="MyDataGrid" runat="server" Width="700" BackColor="white" BorderColor="black" CellPadding="3" CellSpacing="0" Font-Size="9pt" AutoGenerateColumns="False" HeaderStyle-BackColor="darkred" HeaderStyle-ForeColor="white">
<asp:CheckBox ID="CheckAll" OnClick="javascript: return select_deselectAll (this.checked, this.id);"
runat="server" />
<font face="Webdings" color="white" size="4">a</font>
<asp:CheckBox ID="DeleteThis" OnClick="javascript: return select_deselectAll (this.checked, this.id);"
runat="server" />
// ... Rest of our Custom Template & Bound Columns

The code listed above is what makes our DataGrid set up behave just like the grids on Hotmail and Yahoo. Our .NET DataGrid will have the same functionality and options available for selecting however many items, or perhaps all, that you'd like to delete, and once you do and submit, kiss them goodbye.

Selecting and De-Selecting our Checkboxes

Now that both checkboxes are wired to our multi-faceted JavaScript method, how is that one function going to determine the checkbox its dealing with, and the action it needs to carry out? Ah, here's how :-)

Our function select_deselectAll, listed below, accepts two arguments: the Checkbox's checked value, and its ID. Once this function is called, and its two arguments have been passed in, it'll begin looping through our form. Next, it begins performing some conditional checking utilizing JavaScript's indexOf method to locate the appropriate checkbox, and is based on both the values passed in, which it turn ultimately will give us one of several causes and effects:

If the main "select all" checkbox is checked, it will select all of the DataGrid checkboxes
If the main "select all" checkbox is unchecked, then all of the DataGrid checkboxes get unselected
Finally, if after the main "select all" checkbox is selected and all of the DataGrid's checkboxes are all checked, any one of those checkboxes gets unchecked, then the main checkbox is also unchecked. This way we don't end up having our checkbox's logic behaving inconsistently or erratically.

function select_deselectAll (chkVal, idVal)
var frm = document.forms[0];
// Loop through all elements
for (i=0; i<frm.length; i++)
// Look for our Header Template's Checkbox
if (idVal.indexOf ('CheckAll') != -1)
// Check if main checkbox is checked, then select or deselect datagrid checkboxes
if(chkVal == true)
frm.elements[i].checked = true;
frm.elements[i].checked = false;
// Work here with the Item Template's multiple checkboxes
else if (idVal.indexOf ('DeleteThis') != -1)
// Check if any of the checkboxes are not checked, and then uncheck top select all checkbox
if(frm.elements[i].checked == false)
frm.elements[1].checked = false; //Uncheck main select all checkbox


Figure 2 shows you the effect of the JavaScript above interacting with the DataGrid when selecting the top main "select all" checkbox.

Figure 2

Now, aside from this function allowing a quick full selection, you also have the option of manually selecting as many checkbox items as you wish. Next comes the tricky part in how to determine which ones were selected, and how to confirm this the instant you submit the form, and prior to actual deletion.

Confirming Multiple Deletes

In this section, we'll examine how to confirm multiple deletes when we submit our form. Below in Figure 3 you can now see the alert confirmation after selecting a couple of items, and then submitting the form by press the "Delete Items" button. The alert takes place at any time you submit the form (as long as you have more than one checkbox selected).

Figure 3

Note that this confirmation will alert with all checkboxes selected or a just a few as shown. Pressing the Delete Items button with none selected will not prompt any alert. Here now is how we determine what checkboxes are actually checked.

The first thing we did was set up our Delete Button at the end of our DataGrid; just a regular asp server button. We also wired a server-side event to it - DeleteStore - that, when confirmed, will delete the records:

<asp:Button Text="Delete Items" OnClick="DeleteStore" ID="Confirm" runat="server" />

But how does that pop-up alert confirmation appear? Well, that's the cool thing. We get this by adding the code listed below to our Button server control as soon as the page loads, in our Page_Load method, by locating it using the FindControl method and then adding to the button attributes, like so:

WebControl button = (WebControl) Page.FindControl("Confirm");
button.Attributes.Add ("onclick", "return confirmDelete (this.form);");

So, the second the page loads, it attached the Javascript handler to this button, and if you examine the HTML source code, the button afterwords, actually looks like this:

<input type="submit" name="Confirm" value="Delete Items" id="Confirm" onclick="return confirmDelete (this.form);" />

Cool huh? Now, the second this button is pressed, is when it can now trigger the client side JavaScript function below:

function confirmDelete (frm)
// loop through all elements
for (i=0; i<frm.length; i++)
// Look for our checkboxes only
if (frm.elements[i].name.indexOf("DeleteThis") !=-1)
// If any are checked then confirm alert, otherwise nothing happens
return confirm ('Are you sure you want to delete your selection(s)?')

Ok, what happening here? Well, the JS function above is, for all intents and purposes, not that different from the previous JavaScript function - select_deselectAll. Except, instead of determining if the main "select all" checkbox is checked, it actually checks to see whether if any of the DataGrid row checkboxes are checked. If so, it'll then, and only then, alert you with a confirmation to proceed onto either to delete or cancel.

Deleting Data

Now recall our asp:button above, and its default JavaScript onclick event handler attached on Page_Load. Aside from this we also notice it has another OnClick event (this one being server based) that gets raised when the button is clicked, rather pressed, that'll allow it to fire the server-side DeleteStore method to delete our data:

public void DeleteStore (Object sender, EventArgs e)
string dgIDs = "";
bool BxsChkd = false;
foreach (DataGridItem i in MyDataGrid.Items)
CheckBox deleteChkBxItem = (CheckBox) i.FindControl ("DeleteThis");
if (deleteChkBxItem.Checked)
BxsChkd = true;
// Concatenate DataGrid item with comma for SQL Delete
dgIDs += ((Label) i.FindControl ("StoreID")).Text.ToString() + ",";
// Set up SQL Delete statement, using LastIndexOf to remove tail comma from string.
string deleteSQL = "DELETE from Stores WHERE stor_id IN (" + dgIDs.Substring (0, dgIDs.LastIndexOf (",")) + ")";

if (BxsChkd == true)
{ // Execute SQL Query only if checkboxes are checked, otherwise error occurs with initial null string
SqlHelper.ExecuteNonQuery (objConnect, CommandType.Text, deleteSQL);
OutputMsg.InnerHtml += "<font size=4><b>Store information has been deleted.</b></font>";
OutputMsg.Style["color"] = "green";
catch (SqlException err)
OutputMsg.InnerHtml += err.Message.ToString(); //"<font size=4><b>An error occurred and the record could not be deleted</b></font>";
OutputMsg.Style["color"] = "red";
//Refresh data

Since having wired the two client/server methods together, it's our JavaScript code that actually intercepts this button's call and goes first. If you confirm OK, then will the deleting server-side method execute, otherwise it'll cancel all events after that point and prevent anything from posting back.

Looking at the DeleteStore() method, you'll notice that it is actually does a few things. First, it set's up the string variable dgIDs that will hold all of our selected DataGrid IDs. Next, it loops through the DataGrid, and gathers all of the selected item ids that are based on the row's TemplateColumn ID, which is why I kept the ID control as a TemplateColumn and the rest BoundColumns as these types of controls do not support the ID property we need for referencing our data. After this, it will, upon verifying checked items, gather all the ids and assign them to our dgIDs variable, that'll be used with our SQL deleteSQL delete statement.

The deleteSQL delete statement uses the "WHERE IN" argument to perform the multiple deletes in one shot. Since we need to separate each id with a comma, you'll notice that in the loop I attach a comma after each collected item. This way we'll have all of our items clearly defined in our SQL. One problem however is that since we add on a comma after each collected item, the last one as well will include a tail-end comma and SQL won't like this. For example, once we loop through the DataGrid, gather up all of the selected items, and assign it to our delete string we could end up with something like this:

DELETE from Stores WHERE stor_id IN (2,4,6,7,)

Notice the last comma; that's a no-no. To quickly and easily remedy this, we must remove the last comma, and we do this by pulling the substring we need from the "dgIDs" string using LastIndexOf (",") effectively removing the last comma, and properly formatting the delete statement for SQL, like so:

DELETE from Stores WHERE stor_id IN (2,4,6,7)

Finally, DeleteStore proceeds to execute the query against the database. Incidentally, for those wondering why I have a conditional with BxsChkd? Well it's because if I don't initially select any items, I'm returned an error on Page_Load due to our SqlHelper having nothing initialized. Therefore, by do so, our DeleteStore method will remain silent, and happily waiting in the wings until it does get the actual go ahead.

So that's the crux of our DataGrid application, and technology behind doing multiple checkbox deletes.


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