ASP.Net

Triggering a validator through javscript

Jonas Bush — Mon, 29 Jan 2007 22:45:00 GMT

In this post, I talked about enabling or disabling a validator client-side. Someone had commented asking how to change the status of a control from valid to invalid. The following javascript works at least for required field validators, I haven't tested it with anything else (but I imagine it should work just fine). Again, this is 2.0, I haven't tested this in 1.1:

var myValidator = document.getElementById('<%=reqField.ClientID%>');
ValidatorValidate(myValidator);

For a required field validator at least, the causes the same actions as clicking on a button on the page.

Hope this helps!

Using Atlas to act as a check on javascript calls

Jonas Bush — Wed, 16 Aug 2006 21:48:00 GMT

One of the things I've been working on is how to use Atlas web services to verify actions on the server. So the client requests to perform a particular action on the server, and if they don't have access to perform that action or the action fails (because a database is down, or something along those lines), I don't want the method on the client to continue executing.

The problem with that is that Atlas web service calls are asynchronous by nature (explained here and here). So I can't say something like this:

if(myService.myServiceCall() == true)
{
//do stuff
}

What I've come up with is this javascript object:

function webServiceRunner(webServiceFunction, returnFunction, returnParams)
{
var _returnFunction = returnFunction;
var _returnParams = returnParams;
var _webServiceFunction = webServiceFunction;

this.runService = function()
{
_webServiceFunction(onServiceComplete);
}

function onServiceComplete(result)
{
    var r = '_returnFunction(';
    for(var i = 0; i < _returnParams.length; i++)
    {
      r += '_returnParams[' + i.toString() + ']';
      if(i < returnParams.length - 1)
        r += ',';
    }
    r += ', result);';
    //alert(r);
    eval(r);
  }
}

This takes advantage of some of the nice (and dangerous) features of Javascript, the eval() statement, the arguments object, and function pointers. Eval() will let you create a string, like var s = 'alert(“hi“);'; - and then call eval(s); - the end result of which will be “Hi“ showing up in an alert box. The arguments object is created automatically for you in javascript inside of any function, and contains an array of all the arguments passed into that function.

So now I can instantiate and call this class like so:

<span class="CommandLink" onclick="testOne(this);">Testspan>

Assuming I have a webservice defined, as well as the proper Atlas script manager setup:

<atlas:scriptmanager id="scriptManager" runat="server">
<services>
<atlas:servicereference path="TestWebService.asmx" />
services>
atlas:scriptmanager>

[WebMethod]
public bool HasAccess()
{
return false;
}

What ends up happening inside the webServiceRunner is that the following string will be created:

_returnFunction(_returnParams[0], result);

Then that string is eval-ed, and my original testOne function is called, with the original sender object (from the original click), and the result parameter from the web service.

If this is confusing, post a comment or send me an email and I'll try and elaborate further. If you think this is silly or useless, leave a comment and explain why. :)

Disabling an ASP.Net Validator through Javascript

Jonas Bush — Fri, 11 Aug 2006 15:57:00 GMT

If you ever find yourself needing to selectively disable an asp.net validator through javascript, you can do the following (in 2.0, not sure if this exists in 1.x):

function doSomething()
{
var myVal = document.getElementById('myValidatorClientID');
ValidatorEnable(myVal, false);
}

Quick and easy! Sadly, not as easy to find through Google, so hopefully this post will help that. :)

Enabling/disabling asp.net checkboxes through javascript

Jonas Bush — Fri, 28 Jul 2006 05:10:00 GMT

The problem:

You want to have a web form with multiple checkboxes, and have some of them be enabled or disabled depending on whether a certain checkbox is checked (or radio button selected, or what have you).

At first glance, this seems fairly simple; you can just do:

<%=myCheckBox.ClientID%>.disabled = false;

in javascript.

The problem comes when you, on the server side, disable the checkbox by default. (NB: this pertains to ASP.Net 2.0, it may work differently in 1.x). The problem is that an <asp:checkbox /> control gets rendered out like this:

The real problem comes when you have a checkbox like this: <asp:checkbox enabled=”false” />. This gets rendered out like this:

Can you see the problem? In our javascript, when we enable the input, we're not enabling the surrounding span. As it happens, in FireFox, this doesn't seem to be an issue (the checkbox will be enabled as you would expect). In IE6, however, the checkbox will be disabled because the surrounding span is disabled.

To get around this, you can do the following instead of saying myCheckBox.Enabled = false in your code-behind:

myCheckBox.InputAttributes.Add(”disabled”, “disabled”);

(There's also a “LabelAttributes” property of the checkbox, if your control has text that you want to give attributes to explicitly).

Hope this helps!

Less than useful helpfiles, part 1

Jonas Bush — Tue, 09 May 2006 20:37:00 GMT

In the helps for HtmlInputControl.Name (for .NET 2.0):

Gets or sets the unique identifier name for the HtmlInputControl control.

Later on, in that same help file:

In this implementation, the get accessor returns the value of the Control.UniqueID property. However, the set accessor does not assign a value to this property.

So then why say that it sets the property, if it doesn't actually set the property?

Repeaters, Checkboxes and UpdatePanels, Oh My!

Jonas Bush — Mon, 08 May 2006 21:08:00 GMT

I was working on some sample stuff that I'll be posting later and ran into a problem. I had 2 different update panels; inside one was just a div, inside the other one was a repeater. Inside the repeater I had a bunch of checkboxes, and when I checked/unchecked them, I needed the first update panel to be updated. This posed a couple of problems:

A checkbox doesn't have a CommandName property, and can't be used to trigger a Repeater's ItemCommand event

This I got around by declaring the event handler for the checkbox in the markup: OnCheckedChanged=”myCB_OnCheckedChanged”, and in the event handler I can cast the sender argument to a checkbox. The other problem:

An UpdatePanel's list of triggers can't include a control that's inside a template

Which means I can't say <atlas:ControlEventTrigger ControlID=”myCB” EventName=”myCB_OnCheckedChanged” />, since myCB doesn't actually exist at runtime. Instead, in myCB_OnCheckedChanged, I can just say: updatePanel1.Update(); and everything works fine.

Hope this helps...

Custom Server Controls in 2.0

Jonas Bush — Thu, 06 Apr 2006 15:29:00 GMT

Ahh the joys of learning new tech. :)

In 2.0, if you have a custom server control in your app_code directory, it must have a namespace, and the register directive in a page that uses that control should look like this:

<%@ register namespace="TestWebControls" tagprefix="testControl" %>

And this would be the code in your App_Code folder:

namespace TestWebControls
{
[ParseChildren(false)]
[PersistChildren(true)]
[ToolboxData("<{0}:TestControl runat=\"server\"")]
[AspNetHostingPermission(System.Security.Permissions.SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(System.Security.Permissions.SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class TestServerControl : System.Web.UI.WebControls.WebControl
{
public override void RenderBeginTag(HtmlTextWriter writer)
    {
      this.AddAttributesToRender(writer);
      writer.RenderBeginTag("div");
    }
    public override void RenderEndTag(HtmlTextWriter writer)
    {
      writer.RenderEndTag();
    }
  }
}

Then in your markup, you would have:

<testControl:TestServerControl cssclass="Foo" id="foo1" runat="server">
inside
testControl:TestServerControl>

the "TestServerControl" name must match the name of the class of your custom server control (which I overlooked...whoops). You can also register the control in your web.config for ease of use in multiple pages:

<system.web>
   <pages>
      <controls>
         <add namespace="TestWebControls" tagPrefix="testControl" />
      controls>
   pages>
system.web>

Since this control is only going to be used in this app, I don't need to put it in a separate dll. But if you do put it in a separate dll, all you need to add is the "assembly" attribute when registering your controls. Note that you can't add the control to your toolbox unless it's compiled into a separate dll.