Question

This is probably a really simple thing. Basically, the user clicks a button and a potentially long running task happens. I’d like to do a few things like toggle the button’s enabled state, show a spinner, etc. In VB.NET Winforms I’d just do Application.DoEvents() and the updates would happen and the code can continue. How can I do this in ASP.NET? (preferable serverside or minimal javascript)

Answer 1

There are a few ways to approach this in ASP.Net depending on exactly what your requirement is. Getting the process started is fairly easy, but monitoring it for completion from the client side will require more work in both the server and the client.

The basic outline of the solution is:

1) Perform some action on the client that initiates the action. For example, you could post the entire page back on a button click, initiate an ajax request, or have a partial page postback depending on how much information you need from the page.

2) On the server side, initiate the task using a BackgroundWorker, make an entry in a workflow queue, or store a request in a database table that is monitored by a service that is responsible for performing the action.

3) Back on the client side, use javascript start a window.timeout loop that, when it times out, issues an ajax request to the web server to check on the completion. Using a timeout loop like this will ensure that the UI remains responsive and that any animations being displayed will display correctly. How you check on the completion will depend on how your server-side implementation is designed, but will almost certainly require a database.

We use the following general approach for initiating reports from the web client, which can be long running:

When the user initiates the report, open a new window to the report generation page on the client using javascript, passing the page enough parameters to get it started. Opening a separate window allows the user to continue working, but still see that there is something happening.

The user interface for the report page basically contains an animated GIF so that the user knows that something is going on.

When the report page is initially loaded on the server, it generates a unique id for monitoring the status of the report and embeds this in javascript for use in monitoring the status. It then stores this unique identifier in a database table that contains the unique id and a status column, initializing the status to requested.

Once the database entry has been made, the page fires off a BackgroundWorker to initiate the action and then returns the page to the user.

When the page is displayed, javascript starts a window.timeout loop that periodically fires off an ajax request to the web server, which then checks the database for the status of the report using the unique identifier created earlier.

When the backgroundworker finishes the report, either successfully or in failure, it updates the database table with the status, location of the report or error messages and terminates.

When the javascript loop finds that the report generation has completed, it either displays the error message or the report to the user.

Hopefully, this gives you some ideas for solving your issue.