Adding Client-Side Message Boxes in your ASP.NET Web Pages, Part 2By Tim Stall
In Part 1 we examined how to add confirm message boxes in an ASP.NET Web page. In this final part, we'll look at how to display alert message boxes.
Displaying Alert Message Boxes
Besides having prompting the user to confirm that they want to perform an action, we might also want to notify the user of some server-side behavior. For example, if there was some server-side error and the data entered wasn't correctly saved, we might want to use an alert message box to inform the user. Or perhaps when attempting to add the data provided into the database, we deduced that the provided data was duplicate data. The question becomes, coming back from the server to the client, how would we alert the user with a message box?
onload event that
generated a message box. However like the previous case, ASP.NET provides us additional methods to handle all this
from the code-behind without having to hard code HTML ourselves.
What we want to do is register a client script block with the ASP.NET Web page. More specifically, we want this to
run when the page starts up on the client. Again it's our lucky day, as the ASP.NET
Page class provides
RegisterStartupScript() method for that very purpose.
Typically what will happen is the user will submit his data, we'll do some processing, and then realize that we need
to alert the user of some unexpected behavior. Therefore, we'll probably need to add this
method call in the Button Web control's server-side
Click event handler. The code for this might look
This code first generates the message by checking field values (in this case if a CheckBox1 CheckBox Web control was checked or not) and building the message appropriately. However note that the message could be generated from any server-side process, such as the return value of a business object, or based upon the results of a stored procedure or database query.
RegisterStartupScript() method takes two string inputs: a key, identifying the script block being
registered, and the actual script itself. Notice that the second input parameter, the client-side script, includes
RegisterStartupScript() it is prudent to first check to make sure that the script block
hasn't already been registered. (In our simple example above, it clearly couldn't have already been registered, but
if you are registering a script block based on, say, values in a DataGrid, there might be multiple records that would
cause the script block to be rendered. A check to
IsStartupScriptRegistered() quickly determines if
a startup script has already been registered or not.)
Like the previous sample, we can also abstract this functionality to a
For this method, we need to pass in a
Page class instance (since the
IsStartupScriptRegistered() methods are methods of the
Page class), along with the
string to display in the alert message box and the key name by which to register the script.
The original page could then call the
CreateMessageAlert() method like so:
Notice that when calling the
CreateMessageAlert() method we pass in
Me for the
instance. This is because the code-behind class is inherited from the
Page class, so we can just
pass in the code-behind class reference. The second parameter is the message to display in the alert message box and
the third input parameter provides the key name for the script block.
In this article we looked at how to add client-side message boxes to your ASP.NET application. Adding confirm message boxes is as simple as adding an
onclickattribute to the Button Web control's
Attributescollection. Displaying an alert message box on page load involves calling the