Please wait dialog & downloading files in asp.net

Question

Hello,

In my ASP.Net application I have a requirement that when a user clicks on an UI element we generate a PDF for them which they can download. This is currently implemented by doing a form post to an ashx page. This page essentially inspects the form and then executes the correct server side page which either results in HTML or a PDF document of that pages HTML.

On the client I know ahead of time if we are going to be getting a PDF or HTML, when its an HTML I open a new window and direct the form post to that window and all works well. When its a PDF I don't change the target for the form and it remains on the current page.

This works, the user is presented with a save dialog, and the current page is not changed or lost.

The problem I have is that generating the PDF takes anywhere from 1-15 seconds. What I want to do is popup a please wait dialog. Displaying the popup is going to be easy, what I am not sure of is how do I know to close the popup? The popup will be a div in the current page.

Thanks in advance, Josh

Answer 1

just have some javascript on the client side and let it show some animated GIF for 1-15 seconds (your choice) and close itself after the designated time.

Answer 2

The popup can have a client side timer which polls the server for task completion. The long running server task should update the progress in a database table or a server cache object which can be accessed by the polling service.

Couple of old articles from MSDN magazine. You should be able to use the same concepts with newer libraries like asp.net Ajax.

Reporting Task Progress With ASP.NET 2.0

Simplify Task Progress with ASP.NET "Atlas"

Answer 3

You said:

When its a PDF I don't change the target for the form and it remains on the current page.

If that is the case then the original page will be gone when the PDF is opened. In that situation I would have a loading animated gif and open it using Javascript into a div tag overlaying the rest of the page. You would not need to close it, so no timer or polling needed. It would just be gone when the page is gone.

Answer 4

Gulzar's suggestion was spot on. I have a simple ajax enabled wcf service which checks a session variable. My ashx page sets the variable to false when it starts processing and then true when its done.

I think there might be a race condition if the client checks before we set the session item to false; however, there are ways around that if we modify the service to set the session item to false after a client gets an im done response.

The tricks is still going to be figuring out what the intervalon the client should be. If we set it to low the user could save the file and then see the still processing message. I'm debating myself between half a second and a second. Anything less then a half a second seems unnessecary.