calling clientside js with onchange event

Z

Zeebra3

Here goes: I have a web form with several asp:dropdownlists, with
which, when selection is changed I want to fire an event defined in
some clientside js.

The content of the clientside code is dependant on data collected in
the code behind on the server. I have set AutoPostback to false for
the controls and added lines such as
cboMyCombo1.Attributes.Add("onchange", "MyCombos_OnChange('1')");
in the Page_Load event, which is rendered OK when I view the source of
the page.
I wanted to use RegisterClientScriptBlock to get the client js into
the page, but found that it didn't put the code into the <head> tag,
but into the <form> tag. After some research I deemed it necessary to
get the js into the <head> tag and so I added an id and runat=server
to the head tag.
At design time I have some script already declared in the head tag so
I got the InnerHtml property of the head tag in the Page_Load event
and appended some more script within an additional <script> tags.

When rendered and looking at the source, everything appears to be
where I want it to be on the page. The onchange attributes are there
and the 'MyCombos_OnChange' js function is within the head tag.
However, you've guessed it, I get the good old message
"Microsoft JScript runtime error: Object expected" suggesting that the
'MyCombos_OnChange' function called from the onchange attribute is not
defined.
Interestingly, if I change the cboMyCombo1.Attributes.Add call in
Page_Load to add the attribute onchange and call a function that is
already hard coded into the page, this function is called OK. I have
also tried swapping round the order in which hard coded client js and
dynamic js appears, even taken out all hard coded client js. I just
can't get my onchange event to call a dynamically created js function
even when it is within the head tag.
I may be overlooking something, but I've exhausted all posts similar
to this problem and am now seeking inspiration.
Thanks for any help with this
 
L

Lewis Wang [MSFT]

Hi Davec,

After reviewing the description, I think the question is: You used
InnerHtml property of the head tag in the Page_Load event to add some
JavaScript code into <head> ...</head>, and used
cboMyCombo1.Attributes.Add("onchange", "MyCombos_OnChange('1')") to call
MyCombos_OnChange when the dropdownlist’s onchange event fires. However,
the MyCombos_OnChange was not called as expected and A "Microsoft JScript
runtime error: Object expected" error occurred. Please post here if I have
any misunderstandings.

I have done a test and here is the code snippet. It works well on my
machine; you can try it on your side.

private void Page_Load(object sender, System.EventArgs e)
{
HtmlGenericControl head=(HtmlGenericControl)this.FindControl ("myhead");
head.InnerHtml ="<script language=JavaScript> function
MyCombos_OnChange(i){alert(i);}</script>";
DropDownList1.Attributes.Add("onchange","MyCombos_OnChange('1')");
}

<HEAD id ="myhead" runat =server >
...
...
</HEAD>


<form id="Form1" method="post" runat="server">
<asp:DropDownList id="DropDownList1" style="Z-INDEX: 101; LEFT: 128px;
POSITION: absolute; TOP: 80px" runat="server">
<asp:ListItem >1</asp:ListItem>
<asp:ListItem >2</asp:ListItem>
<asp:ListItem >3</asp:ListItem>
</asp:DropDownList>
</form>

Additionally, please check the rendered html and find if it is correct on
the client side. If the problem is still not resolved, please past some
lines of code here then I might be able to work out what the problem is.

Best regards,
Lewis

This posting is provided "AS IS" with no warranties, and confers no rights.

--------------------
| From: (e-mail address removed) (Zeebra3)
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| Subject: calling clientside js with onchange event
| Date: 5 Aug 2003 09:15:22 -0700
| Organization: http://groups.google.com/
| Lines: 36
| Message-ID: <[email protected]>
| NNTP-Posting-Host: 193.132.206.100
| Content-Type: text/plain; charset=ISO-8859-1
| Content-Transfer-Encoding: 8bit
| X-Trace: posting.google.com 1060100123 10612 127.0.0.1 (5 Aug 2003
16:15:23 GMT)
| X-Complaints-To: (e-mail address removed)
| NNTP-Posting-Date: 5 Aug 2003 16:15:23 GMT
| Path:
cpmsftngxa06.phx.gbl!TK2MSFTNGP08.phx.gbl!newsfeed00.sul.t-online.de!t-onlin
e.de!peernews3.colt.net!news0.de.colt.net!news-fra1.dfn.de!npeer.de.kpn-euro
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| Xref: cpmsftngxa06.phx.gbl microsoft.public.dotnet.framework.aspnet:165025
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| Here goes: I have a web form with several asp:dropdownlists, with
| which, when selection is changed I want to fire an event defined in
| some clientside js.
|
| The content of the clientside code is dependant on data collected in
| the code behind on the server. I have set AutoPostback to false for
| the controls and added lines such as
| cboMyCombo1.Attributes.Add("onchange", "MyCombos_OnChange('1')");
| in the Page_Load event, which is rendered OK when I view the source of
| the page.
| I wanted to use RegisterClientScriptBlock to get the client js into
| the page, but found that it didn't put the code into the <head> tag,
| but into the <form> tag. After some research I deemed it necessary to
| get the js into the <head> tag and so I added an id and runat=server
| to the head tag.
| At design time I have some script already declared in the head tag so
| I got the InnerHtml property of the head tag in the Page_Load event
| and appended some more script within an additional <script> tags.
|
| When rendered and looking at the source, everything appears to be
| where I want it to be on the page. The onchange attributes are there
| and the 'MyCombos_OnChange' js function is within the head tag.
| However, you've guessed it, I get the good old message
| "Microsoft JScript runtime error: Object expected" suggesting that the
| 'MyCombos_OnChange' function called from the onchange attribute is not
| defined.
| Interestingly, if I change the cboMyCombo1.Attributes.Add call in
| Page_Load to add the attribute onchange and call a function that is
| already hard coded into the page, this function is called OK. I have
| also tried swapping round the order in which hard coded client js and
| dynamic js appears, even taken out all hard coded client js. I just
| can't get my onchange event to call a dynamically created js function
| even when it is within the head tag.
| I may be overlooking something, but I've exhausted all posts similar
| to this problem and am now seeking inspiration.
| Thanks for any help with this
|
 
V

Vidar Petursson

Hi

It should not matter that the onchange function is in the form tag
--------------8<---------
<html>
<head>
</head>
<body>
<form>
<script language="JavaScript">
function doIt(e){
alert(e.selectedIndex);
}
</script>
<select name="mySelect" onchange="doIt(this)">
<option value="1">1</option>
<option value="2">2</option>
</select>
</form>
</body>
</html>
------------->8----------------------

Post the code generated for the onchange handler.....

--
Best Regards
Vidar Petursson
==============================
Microsoft Internet Client & Controls MVP
==============================
 
Z

Zeebra3

Hi again, confusion reigns. Thanks for your reponses Lewis and Vidar,
much appreciated. Let me tie this thing up.
Firstly Lewis. The only differences in principle between what you
posted and what I had done, was that I was appending additional script
onto the end of the contents of the Head innerhtml and I also had the
comment tags within the script. Now I know these are small things but
bear with me.
The script function that I was embedding into the page was built up as
a string on the serverside and looked similar to this
<script language="javascript"><!--function
doThis(arg){window.alert("Hi there");}--></script>
This was being appended to the head innerhtml which already contained
some js functions within script tags, something like
<script language="javascript">
<!--
function myFunct(){
window.alert("hello");
}
-->
</script>
After posting I managed to get my dynamic code working by inserting it
into the existing script tag before the first existing function.

The crucial difference was that because I was inserting it into
existing script tags, I had taken out the <!-- --> comments as they
were already present. It seemed that they were causing the failure due
to the fact that I had no line breaks around them.

And so Vidar, you are correct. Once I had ensured that the script had
the comment tags on separate lines, I could indeed use
RegisterClientScriptBlock to add the code into the form tag, with no
problems.

All's well that ends well, and thanks again for your responses.
 
L

Lewis Wang [MSFT]

Hi Davec,

I am glad to hear you had found where the problem is. Thank you for sharing
the knowledge in the newsgroup.

Have a nice day.

Lewis

This posting is provided "AS IS" with no warranties, and confers no rights.


--------------------
| From: (e-mail address removed) (Zeebra3)
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| Subject: Re: calling clientside js with onchange event
| Date: 8 Aug 2003 02:15:29 -0700
| Organization: http://groups.google.com/
| Lines: 34
| Message-ID: <[email protected]>
| References: <[email protected]>
| NNTP-Posting-Host: 193.132.206.100
| Content-Type: text/plain; charset=ISO-8859-1
| Content-Transfer-Encoding: 8bit
| X-Trace: posting.google.com 1060334130 21829 127.0.0.1 (8 Aug 2003
09:15:30 GMT)
| X-Complaints-To: (e-mail address removed)
| NNTP-Posting-Date: 8 Aug 2003 09:15:30 GMT
| Path:
cpmsftngxa06.phx.gbl!TK2MSFTNGP08.phx.gbl!newsfeed00.sul.t-online.de!t-onlin
e.de!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!sn-xit-03!sn-xit-01!sn-
xit-09!supernews.com!postnews1.google.com!not-for-mail
| Xref: cpmsftngxa06.phx.gbl microsoft.public.dotnet.framework.aspnet:166054
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| Hi again, confusion reigns. Thanks for your reponses Lewis and Vidar,
| much appreciated. Let me tie this thing up.
| Firstly Lewis. The only differences in principle between what you
| posted and what I had done, was that I was appending additional script
| onto the end of the contents of the Head innerhtml and I also had the
| comment tags within the script. Now I know these are small things but
| bear with me.
| The script function that I was embedding into the page was built up as
| a string on the serverside and looked similar to this
| <script language="javascript"><!--function
| doThis(arg){window.alert("Hi there");}--></script>
| This was being appended to the head innerhtml which already contained
| some js functions within script tags, something like
| <script language="javascript">
| <!--
| function myFunct(){
| window.alert("hello");
| }
| -->
| </script>
| After posting I managed to get my dynamic code working by inserting it
| into the existing script tag before the first existing function.
|
| The crucial difference was that because I was inserting it into
| existing script tags, I had taken out the <!-- --> comments as they
| were already present. It seemed that they were causing the failure due
| to the fact that I had no line breaks around them.
|
| And so Vidar, you are correct. Once I had ensured that the script had
| the comment tags on separate lines, I could indeed use
| RegisterClientScriptBlock to add the code into the form tag, with no
| problems.
|
| All's well that ends well, and thanks again for your responses.
|
 
P

pelegk1

Joined
Jul 15, 2007
Messages
3
Reaction score
0
script language="javascript" issue

i needed the same as u did for my code
i first wrote
script language="text/javascript"
beacus i read in some places that its the correct way towrite like that
and i did so
when i did it i get he error : "object expected"
any idea why?
thnaks in advance
peleg
 

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