Styling ASP.NET MVC Error Messages
- by MightyZot
Originally posted on: http://geekswithblogs.net/MightyZot/archive/2013/11/11/styling-asp.net-mvc-error-messages.aspxOff the cuff, it may look like you’re stuck with the presentation of your error messages (model errors) in ASP.NET MVC. That’s not the case, though. You actually have quite a number of options with regard to styling those boogers. Like many of the helpers in MVC, the Html.ValidationMessageFor helper has multiple prototypes. One of those prototypes lets you pass a dictionary, or anonymous object, representing attribute values for the resulting markup. @Html.ValidationMessageFor( m => Model.Whatever, null, new { @class = “my-error” }) By passing the htmlAttributes parameter, which is the last parameter in the call to the prototype of Html.ValidationMessageFor shown above, I can style the resulting markup by associating styles to the my-error css class. When you run your MVC project and view the source, you’ll notice that MVC adds the class field-validation-valid or field-validation-error to a span created by the helper. You could actually just style those classes instead of adding your own…it’s really up to you. Now, what if you wanted to move that error message around? Maybe you want to put that error message in a box or a callout. How do you do that? When I first started using MVC, it didn’t occur to me that the Html.ValidationMessageFor helper just spits out a little bit of markup. I wanted to put the error messages in boxes with white backgrounds, our site originally had a black background, and show a little nib on the side to make them look like callouts or conversation bubbles. Not realizing how much freedom there is in the styling and markup, and after reading someone else’s post, I created my own version of the ValidationMessageFor helper that took out the span and replaced it with divs. I styled the divs to produce the effect of a popup box and had a lot of trouble with sizing and such. That’s a really silly and unnecessary way to solve this problem. If you want to move your error messages around, all you have to do is move the helper. MVC doesn’t appear to care where you put it, which makes total sense when you think about it. Html.ValidationMessageFor is just spitting out a little markup using a little bit of reflection on the name you’re passing it. All you’ve got to do to style it the way you want it is to put it in whatever markup you desire. Take a look at this, for example… <div class=”my-anchor”>@Html.ValidationMessageFor( m => Model.Whatever )</div> @Html.TextBoxFor(m => Model.Whatever) Now, given that bit of HTML, consider the following CSS… <style> .my-anchor { position:relative; } .field-validation-error { background-color:white; border-radius:4px; border: solid 1px #333; display: block; position: absolute; top:0; right:0; left:0; text-align:right; } </style> The my-anchor class establishes an anchor for the absolutely positioned error message. Now you can move the error message wherever you want it relative to the anchor. Using css3, there are some other tricks. For example, you can use the :not(:empty) selector to select the span and apply styles based upon whether or not the span has text in it. Keep it simple, though. Moving your elements around using absolute positioning may cause you issues on devices with screens smaller than your standard laptop or PC. While looking for something else recently, I saw someone asking how to style the output for Html.ValidationSummary. Html.ValidationSummery is the helper that will spit out a list of property errors, general model errors, or both. Html.ValidationSummary spits out fairly simple markup as well, so you can use the techniques described above with it also. The resulting markup is a <ul><li></li></ul> unordered list of error messages that carries the class validation-summary-errors In the forum question, the user was asking how to hide the error summary when there are no errors. Their errors were in a red box and they didn’t want to show an empty red box when there aren’t any errors. Obviously, you can use the css3 selectors to apply different styles to the list when it’s empty and when it’s not empty; however, that’s not support in all browsers. Well, it just so happens that the unordered list carries the style validation-summary-valid when the list is empty. While the div rendered by the Html.ValidationSummary helper renders a visible div, containing one invisible listitem, you can always just style the whole div with “display:none” when the validation-summary-valid class is applied and make it visible when the validation-summary-errors class is applied. Or, if you don’t like that solution, which I like quite well, you can also check the model state for errors with something like this… int errors = ViewData.ModelState.Sum(ms => ms.Value.Errors.Count); That’ll give you a count of the errors that have been added to ModelState. You can check that and conditionally include markup in your page if you want to. The choice is yours. Obviously, doing most everything you can with styles increases the flexibility of the presentation of your solution, so I recommend going that route when you can. That picture of the fat guy jumping has nothing to do with the article. That’s just a picture of me on the roof and I thought it was funny. Doesn’t every post need a picture?
