You can subclass HandleErrorAttribute
and override its OnException
member (no need to copy) so that it logs the exception with ELMAH and only if the base implementation handles it. The minimal amount of code you need is as follows:
using System.Web.Mvc;
using Elmah;
public class HandleErrorAttribute : System.Web.Mvc.HandleErrorAttribute
{
public override void OnException(ExceptionContext context)
{
base.OnException(context);
if (!context.ExceptionHandled)
return;
var httpContext = context.HttpContext.ApplicationInstance.Context;
var signal = ErrorSignal.FromContext(httpContext);
signal.Raise(context.Exception, httpContext);
}
}
The base implementation is invoked first, giving it a chance to mark the exception as being handled. Only then is the exception signaled. The above code is simple and may cause issues if used in an environment where the HttpContext
may not be available, such as testing. As a result, you will want code that is that is more defensive (at the cost of being slightly longer):
using System.Web;
using System.Web.Mvc;
using Elmah;
public class HandleErrorAttribute : System.Web.Mvc.HandleErrorAttribute
{
public override void OnException(ExceptionContext context)
{
base.OnException(context);
if (!context.ExceptionHandled // if unhandled, will be logged anyhow
|| TryRaiseErrorSignal(context) // prefer signaling, if possible
|| IsFiltered(context)) // filtered?
return;
LogException(context);
}
private static bool TryRaiseErrorSignal(ExceptionContext context)
{
var httpContext = GetHttpContextImpl(context.HttpContext);
if (httpContext == null)
return false;
var signal = ErrorSignal.FromContext(httpContext);
if (signal == null)
return false;
signal.Raise(context.Exception, httpContext);
return true;
}
private static bool IsFiltered(ExceptionContext context)
{
var config = context.HttpContext.GetSection("elmah/errorFilter")
as ErrorFilterConfiguration;
if (config == null)
return false;
var testContext = new ErrorFilterModule.AssertionHelperContext(
context.Exception,
GetHttpContextImpl(context.HttpContext));
return config.Assertion.Test(testContext);
}
private static void LogException(ExceptionContext context)
{
var httpContext = GetHttpContextImpl(context.HttpContext);
var error = new Error(context.Exception, httpContext);
ErrorLog.GetDefault(httpContext).Log(error);
}
private static HttpContext GetHttpContextImpl(HttpContextBase context)
{
return context.ApplicationInstance.Context;
}
}
This second version will try to use error signaling from ELMAH first, which involves the fully configured pipeline like logging, mailing, filtering and what have you. Failing that, it attempts to see whether the error should be filtered. If not, the error is simply logged. This implementation does not handle mail notifications. If the exception can be signaled then a mail will be sent if configured to do so.
You may also have to take care that if multiple HandleErrorAttribute
instances are in effect then duplicate logging does not occur, but the above two examples should get your started.
Implementation
There are three different implementations: pseudo-elements, pseudo-classes, and nothing.
- WebKit, Blink (Safari, Google Chrome, Opera 15+) and Microsoft Edge are using a pseudo-element:
::-webkit-input-placeholder
. [Ref]
- Mozilla Firefox 4 to 18 is using a pseudo-class:
:-moz-placeholder
(one colon). [Ref]
- Mozilla Firefox 19+ is using a pseudo-element:
::-moz-placeholder
, but the old selector will still work for a while. [Ref]
- Internet Explorer 10 and 11 are using a pseudo-class:
:-ms-input-placeholder
. [Ref]
- April 2017: Most modern browsers support the simple pseudo-element
::placeholder
[Ref]
Internet Explorer 9 and lower does not support the placeholder
attribute at all, while Opera 12 and lower do not support any CSS selector for placeholders.
The discussion about the best implementation is still going on. Note the pseudo-elements act like real elements in the Shadow DOM. A padding
on an input
will not get the same background color as the pseudo-element.
CSS selectors
User agents are required to ignore a rule with an unknown selector. See Selectors Level 3:
a group of selectors containing an invalid selector is invalid.
So we need separate rules for each browser. Otherwise the whole group would be ignored by all browsers.
::-webkit-input-placeholder { /* WebKit, Blink, Edge */
color: #909;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
color: #909;
opacity: 1;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
color: #909;
opacity: 1;
}
:-ms-input-placeholder { /* Internet Explorer 10-11 */
color: #909;
}
::-ms-input-placeholder { /* Microsoft Edge */
color: #909;
}
::placeholder { /* Most modern browsers support this now. */
color: #909;
}
<input placeholder="Stack Snippets are awesome!">
Usage notes
- Be careful to avoid bad contrasts. Firefox's placeholder appears to be defaulting with a reduced opacity, so needs to use
opacity: 1
here.
- Note that placeholder text is just cut off if it doesn’t fit – size your input elements in
em
and test them with big minimum font size settings. Don’t forget translations: some languages need more room for the same word.
- Browsers with HTML support for
placeholder
but without CSS support for that (like Opera) should be tested too.
- Some browsers use additional default CSS for some
input
types (email
, search
). These might affect the rendering in unexpected ways. Use the properties -webkit-appearance
and -moz-appearance
to change that. Example:
[type="search"] {
-moz-appearance: textfield;
-webkit-appearance: textfield;
appearance: textfield;
}
Best Answer
You could use underscore (
_
) and the helper is intelligent enough to do the rest:And for those who want to achieve the same in pre ASP.NET MVC 3 versions they could: