iPhone: A built in way to show the user a simple warning/alert message

I have a custom built sign up component that I would like to开发者_运维问答 enhance. I would like to show error messages before sending the data to the server (like "invalid email") using a built in alert system (other than modal) if possible. Is there any on iOS? Do I have to build one myself? I saw that some apps show a grey rectangle near the bottom of the screen, is that custom built?

Thanks!

Check out this code sample if you want to use Tweetbot style notifications in your application, these are non modal

http://blog.mugunthkumar.com/coding/ios-code-tweetbot-like-alertpanels/

All iOS alerts are modal (for now). You will have to build your own if you want different functionality, but it isn't too difficult. You can put together a little UIView with a label that is normally hidden. Then just set the text and show it when you need to.