Datagrid and clientside callback events

[Dmitry]

Hi All,

I've been looking at clientside callbacks as a way to update parts of
a page without a postback.

Is there a way of rebinding a datagrid on the client. The scenario
would be something like this:

A work queue is displayed on a page using a datagrid
Items are added to the underlying data source by other components in
the system
A javascript function executes every n seconds and discovers new items
for the queue
the datagrid updates, but importantly, the page does not postback

If we can update the datagrid without a postback it means a user can
be filling out a form on the page, but also gets immediate notice that
new items are in the queue.

As far as I can tell a datarid is just rendered html by the time it
gets to a browser, so it can't be manipulated and rebound from the
client.

In contrast, the treeview client behaviour is a clientside object
which binds to an xml data source and can be rebound through client
script.

So it appears I'd need to create something similar to mimick a
datagrid.

Does anyone have any thoughts?

Thanks

 

[Eliyahu Goldin]

In web technology there is no such a thing as refresh without postback. Any
refresh is originated on the client and the server gets the refresh request
via postback. And there is no such a thing a refreshing only part of a page.
What you can do is to put the grid in a separate iframe and refresh that
iframe only.

Eliyahu

 

[Dmitry]

In web technology there is no such a thing as refresh without postback. Any
refresh is originated on the client and the server gets the refresh request
via postback. And there is no such a thing a refreshing only part of a page.
What you can do is to put the grid in a separate iframe and refresh that
iframe only.

Have a look at:
http://www.dotnetjunkies.com/Tutorial/E80EC96F-1C32-4855-85AE-9E30EECF13D7.dcik

it describes asp.net 2.0's client callback implementation which in
turn is built on the msxml.xmlhttp object which has been around quite
a while. It lets you make calls to server side methods from client
code without posting back the page. So now you know there is a way to
refresh only part of a page ;o)

 

[Eliyahu Goldin]

No, I still don't know. ASP.NET 2.0 has not been released yet and can't be
relied on for commercial product development. Beta is good for playing
around and for learning for future. That's why you won't find many
2.0-related threads in the newsgroups. BTW, you original message doesn't
mention 2.0.

As far as I am aware, solutions based on xmlhttp are hassle to implement in
asp.net. Also they are limited to IE5. Currently, it is not a practical
approach unless you have a very special need for it. Note, that ASP.NET 2.0
shields the developers from working directly with xmlhttp.

Eliyahu

 

[Dmitry]

Agreed 2.0 is only in Beta and I didn't originally mention it.

I disagree that its a hassle to implement - you can get a response
back in three lines of javascript. Another approach, using wininet is
admittedly more fiddly.

I also agree that its limited to ie5+ - but that's another thread ;o)

It may be the case that its usage is not widespread at the moment and
so could represent a very special need. However I think its
interesting that ms have chosen to include it in v2.0 of asp.net
because they perceive there being a demand for it.

Regards

 

[Eliyahu Goldin]

I disagree that its a hassle to implement - you can get a response

back in three lines of javascript. Another approach, using wininet is
admittedly more fiddly.

May be, I didn't try myself.

It may be the case that its usage is not widespread at the moment and
so could represent a very special need. However I think its
interesting that ms have chosen to include it in v2.0 of asp.net
because they perceive there being a demand for it.

100% agree. Demand is for sure there. Waiting for the release...

 

[stephg]

Hi Guys,

let me get on bord with this. I am also deperately looking for re-drawing
only a part of an HTML page like a datagrid and also came accross
ICallBackEventHandler.
Currently I am working with iFrames and am refreshing the iFrame pages. But
as you probably know this is very ugly since the screen flickering drives a
user crazy.
So, I believe that ICallBackEventHandler could be a solution. I took a deep
drive into it, but seem not to manage to implement it properly.
Dmitry, did you manage to update your datagrid by using ICallBackEventHandler?
If so I would appreciate if you can give me some snippet of your code how to
facilitate this.
cheers

 

[Shahid Siddiqui]

There is a superb solution for that:
http://www.thycotic.com/dotnet_remotescripting_client.html

You don't read to do the plubmbing hassle associated with the xmlhttprequest
and now it is browser portable. A beautiful solution: just return a C# data
type from the server and get it converted into javascript type on the
client -- has both synchronous and asynchronous versions.

 

[Dmitry]

I am also deperately looking for re-drawing

only a part of an HTML page like a datagrid and also came accross
ICallBackEventHandler.
Currently I am working with iFrames and am refreshing the iFrame pages. But
as you probably know this is very ugly since the screen flickering drives a
user crazy.
So, I believe that ICallBackEventHandler could be a solution. I took a deep
drive into it, but seem not to manage to implement it properly.
Dmitry, did you manage to update your datagrid by using ICallBackEventHandler?

Stephg,

Well, my original query was as to whether there was a way to work with
the datagrid on the client, but I'm fairly sure there isn't - as far
as the dom is concerned what you see as a datagrid is just a bunch of
html.

The internet explorer treeview clientside behaviour IS an object and
has properties and methods that can be called, so using
ICallBackEventHandler it would be possible to add/retrieve data
without the page flicker.

I can mail you some code showing how to make a request without posting
back - though this is asp.net 1.0 and ICallBackEventHandler is not
available - but the code does the same thing that
ICallBackEventHandler does under the hood.

That will gives you the ability to communicate with the server, but
still no datagrid.

For the datagrid....I'm thinking about creating a javascript object
that binds to html. It would be an html table that uses xml as a
datasource and has methods to add and remove rows. Nothing
particularly fancy, but i've not got time to do it right now.

Why not have a go at rolling your own? Make it an asp.net user/server
control and you can add server side functionality too.

 

[stephg]

Shahid Siddiqui,

thanks for this post. However, it does not seem to fit into my requirements
since remote scripting only accepts strings as input. My datagrids and other
fields on the page are populated by webservices. These webservices expect xml
objects as input and return XmlNodes.
But maby I can use the one or the other part of this Thycotic thing in my
project
Thanks

 

[stephg]

Thanks Dmitry.
In deed I would be interested in this code. If you could send it to my
temporary address at (e-mail address removed).
What I am after is to consume my web service every 10 seconds or so that
expects an XmlDocument object as input and returns an XmlNode object.
I want to display this updated data on the page.
Thanks a lot

 

[Shahid Siddiqui]

May the raw xmlHttpRequest help you, I haven't explored it but it supports
XML -- anything compatible.......Moreover for manipulating the grid on the
client side, the only thing you have is JavaScript as I am doing in my
project but the problem is that if you want to exploit the viewstate on the
server side, how the changes would be reflected in that?
If you don't need viewstate of the grid, its ok otherwise what I guess, you
would have to add some customized code on the server side.

 

[Dmitry]

Thanks Dmitry.
In deed I would be interested in this code. If you could send it to my
temporary address at (e-mail address removed).
What I am after is to consume my web service every 10 seconds or so that
expects an XmlDocument object as input and returns an XmlNode object.
I want to display this updated data on the page.
Thanks a lot

I've sent some code to that address. BTW - for webservices you might
try to track down webservice.htc which was floating around on
microsoft's website

 

[Dmitry]

There is a superb solution for that:
http://www.thycotic.com/dotnet_remotescripting_client.html

You don't read to do the plubmbing hassle associated with the xmlhttprequest
and now it is browser portable. A beautiful solution: just return a C# data
type from the server and get it converted into javascript type on the
client -- has both synchronous and asynchronous versions.

This is an iFrames solution by the looks of the msrsclient.js file.
stephg said he was originally using iFrames but didn't like the screen
flicker. The difference with this is that the iFrame is hidden and
used as a container to return values. Nice cross browser approach.