检查文件存在于变量中

Quite a simple one this I imagine.

I'm submitting a form with text and images.

I validate the text by checking the variable length !=0 etc.

I need an effective way to check if the variable that should have a file within does.

This is the code so far...

if(!$afterphoto){
    $form->setError($field, "After photo not entered");
}

This doesn't seem to be working, what would be a better checker?

Thanks.

Solution to this was to use the following code to check that there were no errors and the file was uploaded:

$afterphoto['error'] != 0