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!

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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/

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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.