Tuesday, 20 February 2007

After a while of thinking and struggling with Control Adapters I was unable to find a good solution to get my Validation Controls render as images. I have came to the following conclusions:

  1. Control Adapters will not help
  2. Overriding each Validator is not a good solution
  3. Creating my own Validation Controls is not a good solution

Given the above, I have once again looked at everything I have learned. I have looked at the html code rendered by the controls and then... solution came to me! It turns out that we don't need ASP.NET to get things working. ASP.NET stands in our way when it comes to handling this task, so why not use a plain old CSS? So I did.

When Validaton Control:

<asp:CompareValidator runat="server" ID="V" ControlToValidate="c1" ControlToCompare="c2" Text="Error Text" ToolTip="Title Text"></asp:CompareValidator>

is rendered on a page it looks more or less like this:

<span id="ctl00_V" title="Title Text" style="color:Red;visibility:hidden;">Error Text</span>

To make a nice image out of it, we need few things. First we need one tradeoff: we have to remove the Text attribute, otherwise it will mess the looks a bit. Next we decorate the server control with a CssClass attribute with a value such as "error". Next we create a style:

  display: -moz-inline-stack;
  display: inline-block;
  background-image: url(error.gif);
  background-repeat: no-repeat;
  height: 16px;
  width: 16px;

Notice in the style few things. First, we need the <span> element to be "inline-block". That is because we need it to have a height and width. Furthermore, FireFox does not support "inline-block" (!!!) but we can use a simple workaround with "-moz-inline-stack" value as described by Nicholas in Pain with inline-block article (also see the comments). By default span (inline element) will only be as large as the text it contain. Since in the proposed solution, there will be no text in the <span> this is needed. Next, we set the background-image to a desired url and set the width and height of an element. That's it!

The important thing to note here is the "inline-block" value for a display property. It is a CSS 2.1 introduced value and browser support may vary. After analyzing the display declaration article on quirksmode, I've came to a conclusion that it should be safe to use this technique. Internet explorer "supports" it. Firefox "supports" it. Opera supports it.

Yet again. ASP.NET stands in the way... If you try to use a Display="Dynamic" property, you will find that the proposed solution does not work with FireFox. After a close analysis I came to a conclusion that it works with IE only by chance. The problem is that the validation scripts used by Validation Controls set elements display property to "inline" in case Display property was set to Dynamic on the server control. Internet Explorer somehow manages to use the value from the style which is "inline-block" and so it works. FireFox uses the "inline" value and so we have an <span> element with no content - an invisible element.

I have currently few ideas of how to overcome this problem. One way it could be done is to put an absolutely positioned Validation Control inside a relatively positioned <div> element like this. Remove the Display="dynamic" attribute and mark the containing div with a class="error" and change the styles as follow:

  position: relative;
  display: inline;
  position: absolute;
  left: 0; top 0;

The positioning of elements needs some work, but hey at least it works!

Complete code here: ValidationControlsAsImages.txt (.54 KB)

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