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.NET Forum / ASP.NET / General / February 2006Does the ASP.Net Panel client side onLoad work?
I'm trying to create a web page and I need a javascript function to be called on the load of a particular panel. (The panel is hidden during some but not all postbacks.) The function is bound to the panel in VB as follows: pnlAdd.Attributes.Add("onLoad", "SetupScreenLite()") This is basically how we attach all functions in our projects but this is the first time I've worked with onLoad and the first time I've tried to attach anything to a panel. Any ideas? "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:DEFBCC18-E3D7-4317-9CD0-0C5C159E0306@microsoft.com: > I'm trying to create a web page and I need a javascript function > to be called on the load of a particular panel. (The panel is [quoted text clipped - 7 lines] > but this is the first time I've worked with onLoad and the first > time I've tried to attach anything to a panel. Any ideas? The panel control generates a <DIV> tag. That tag does not support the onload event: http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/div.asp In fact, the onload event is valid for only a small selection of HTML tags: http://msdn.microsoft.com/workshop/author/dhtml/reference/events/onload.asp Using the page's RegisterStartupScript method may be an alternative way to achieve your goal.  SignatureHope this helps. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ Ok, the problem is this. I am a relative beginner in Javascript. I am trying to develop an ASP.net 1.1 web page. I need a way for a Javascript function to fire once after the load of the page into the browser. What are my options? > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 24 lines] > Using the page's RegisterStartupScript method may be an > alternative way to achieve your goal. add the onload attribute to the page's BODY tag: <BODY onload="myJsFunction();" > Peter SignatureCo-founder, Eggheadcafe.com developer portal: http://www.eggheadcafe.com UnBlog: http://petesbloggerama.blogspot.com > Ok, the problem is this. I am a relative beginner in Javascript. I am > trying to develop an ASP.net 1.1 web page. I need a way for a Javascript [quoted text clipped - 29 lines] > > Using the page's RegisterStartupScript method may be an > > alternative way to achieve your goal. "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:B30FEEFD-F220-4B26-B700-FF2E36DD97A8@microsoft.com: > Ok, the problem is this. I am a relative beginner in > Javascript. I am trying to develop an ASP.net 1.1 web page. I > need a way for a Javascript function to fire once after the load > of the page into the browser. What are my options? As Peter noted, the onload attribute of the <BODY> tag can be used, as can the RegisterStartupScript method. Personally, I prefer to use RegisterStartupScript. It's possible that some browsers have buggy implementations of onload, plus I can insert as much JavaScript as I want with RegisterStartupScript. JavaScript inserted into the onload attribute is realistically limited to method calls and short segments of code that can be expressed in one line. More info on client-side scripting w/ ASP.Net: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/cli entsidescript.asp SignatureHope this helps. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ You refer to 'buggy implementations of onload'. Could this, in practice, result in one or more web controls appearing as nulls (and crashing the script) when the onload function fires, even if the controls have been 'wired' into the Javascript in a conventional fashion? (i.e. document.getElementById("<%= {control-name}.ClientID %>"); > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 18 lines] > > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/cli entsidescript.asp "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:86922A80-B315-45D3-A6E1-3242DBAC6DD6@microsoft.com: > You refer to 'buggy implementations of onload'. > [quoted text clipped - 3 lines] > Javascript in a conventional fashion? (i.e. > document.getElementById("<%= {control-name}.ClientID %>"); I don't think so. Is that line of JavaScript before or after the control in question? The control needs to appear before the JavaScript that accesses it so the browser can put the control in the page's document object model (DOM) tree. For example, this HTML will generate an "object required" error message, because the <INPUT> control comes after the JavaScript that's trying to access that control's value: <HTML> <HEAD> </HEAD> <BODY> <SCRIPT> var value = document.getElementById("myInputBox").value; alert(value); </SCRIPT> <INPUT type="text" id="myInputBox" name="myInputBox" value="Hello, world!"/> </BODY> </HTML> But placing the <INPUT> control before the JavaScript will work: <HTML> <HEAD> </HEAD> <BODY> <INPUT type="text" id="myInputBox" name="myInputBox" value="Hello, world!"/> <SCRIPT> var value = document.getElementById("myInputBox").value; alert(value); </SCRIPT> </BODY> </HTML> This is where the RegisterStartupScript method comes in handy. It always places the JavaScript at the very end of the HTML, just before the closing </FORM> tag. If that's not the problem, what might be happening is either "name mangling" of the ClientID by ASP.Net, or a known bug in .Net 1.1: http://support.microsoft.com/default.aspx?id=818803 Concerning name mangling, when multiple instances of the same user control are present on a page, they cannot all have the same ID in the generated HTML page. Therefore, ASP.Net gives each instance of the control a unique name when it generates the HTML. A control named BlogSideBar1, with an embedded textbox named SearchBox, would be referenced by C#/VB in an .ascx file as BlogSideBar1.SearchBox. However, in the HTML it would appear as _ctl0____ctl0___BlogSideBar1___SearchBox. Your line of code should work, depending on when it's executed in the page's life cycle on the server. If there are multiple instances of "control-name" in your page, that situation might be causing some kind of problem. I generally don't put inline <% %> tags in my pages, except for mundane things like the page's title or meta tags. I prefer to build the JavaScript, complete with ClientIDs, in my code behind files. That way I feel I have better control over exactly what gets sent to the browser, and where it's placed in the page. SignatureHope this helps. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ A worse problem, or perhaps I have misstated the problem. I was testing with the body onload event and it appears that this event only fires once on initial load and does not fire on postbacks. I was assuming otherwise. I need an event that fires on every postback. > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 18 lines] > > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/cli entsidescript.asp "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:E27AAD44-B94B-4FCF-A852-ACF316F1F162@microsoft.com: > A worse problem, or perhaps I have misstated the problem. I was > testing with the body onload event and it appears that this > event only fires once on initial load and does not fire on > postbacks. I was assuming otherwise. I need an event that fires > on every postback. Are you assigning the value to the onload event in the page's Page_Load event? If so, is that assignment in an if/then statement that uses IsPostBack? It sounds like what's happening is this: ::In the Page_Load event:: if not IsPostBack then assign value to <BODY> onload end if The fix is to move the onload assignment outside of that if/then block, so it's always executed when the page is initially created, and after every postback. SignatureHope this helps. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ Thanks, but help me out a little more (Javascript beginner, remember?) I'm drawing a blank. When you say 'assign value to <BODY> onload' , are you referring to something like RegisterStartUpScript or is this yet another Javascript technique I haven't seen yet? > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 21 lines] > block, so it's always executed when the page is initially created, > and after every postback. On second thought, are you refering to giving the body an ID, declaring it in the codebehind, and then doing an <idname>.Attributes.Add("onLoad" etc? Just found an example and I can see it in the HTML source but it doesn't fire. > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 21 lines] > block, so it's always executed when the page is initially created, > and after every postback. "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:334D5DBB-CB22-4812-8C3D-A0718B398D49@microsoft.com: > On second thought, are you refering to giving the body an ID, > declaring it in the codebehind, and then doing an > <idname>.Attributes.Add("onLoad" etc? Yes. The body tag should look something like this in the .aspx file: <BODY runat="server" id="body"> Declare it as an HtmlControl in the code behind file: protected System.Web.UI.HtmlControls.HtmlGenericControl body; And the onload attribute can be assigned like this in the Page_Load event handler: this.body.Attributes["onload"] = "alert('Hello, world!');"; > Just found an example and I can see it in the HTML source but it > doesn't fire. Does the body tag have the runat="server" attribute? SignatureHope this helps. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ Sorry about the number of appends. I moved my code up in the Page_Load codebehind so that it always gets called but the HTML code only fires the first time, never on postback. (but I can still see it in the HTML source) > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 21 lines] > block, so it's always executed when the page is initially created, > and after every postback. "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:C69FDD32-4479-4F5D-A788-E7285BAAD824@microsoft.com: > Sorry about the number of appends. I moved my code up in the > Page_Load codebehind so that it always gets called but the HTML > code only fires the first time, never on postback. (but I can > still see it in the HTML source) That sounds strange. Could you post some code that demonstrates the problem? Thanks. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ Not much to show. In my aspx file I have <body id="body1" runat="server" > In my vb file I have the declaration: ' Protected WithEvents body1 As HtmlGenericControl' (I have tried this both with and without the WithEvents declaration. It apparently has no effect on results.) In the page_load (above the usual test for postback, so it's always called) I have: 'body1.Attributes.Add("onLoad", "alert('test');")' In the HTML source of the postback screen I see: '<body id="body1" onLoad="alert('test');">' But it never fires except on the very first time. > "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" > <BChernick@discussions.microsoft.com> wrote in [quoted text clipped - 14 lines] > C.R. Timmons Consulting, Inc. > http://www.crtimmonsinc.com/ > Not much to show. > [quoted text clipped - 11 lines] > > But it never fires except on the very first time. I'm pretty much out of ideas. If possible, could you post a complete .aspx page that demonstrates the problem? Thanks. SignatureChris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ I should apologize for wasting your time. I've been looking in the wrong place. If you set up a test screen with only the code I have described it works perfectly every time. I suspect that the third party (Telerik) controls we're using are somehow interfering with the postback. > > Not much to show. > > [quoted text clipped - 16 lines] > > Thanks. "=?Utf-8?B?Qi4gQ2hlcm5pY2s=?=" <BChernick@discussions.microsoft.com> wrote in news:381809A1-D4BF-42A6-8D9A-A90EE20196ED@microsoft.com: > I should apologize for wasting your time. I've been looking in > the wrong place. If you set up a test screen with only the code > I have described it works perfectly every time. I suspect that > the third party (Telerik) controls we're using are somehow > interfering with the postback. No problem. Chris. ------------- C.R. Timmons Consulting, Inc. http://www.crtimmonsinc.com/ Free MagazinesGet these publications absolutely FREE for up to 12 months. 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