1) forget about the timing loop (for now). see if you can capture the preview just once and have it appear in the imageview. in fact, that was all i did, and it worked. if you look at the camex class and read erel's comment, you'll see that we're not supposed to use camEx.PreviewImageToJpeg(PreviewPic, 70) in a tight timing loop. i said i used a similar _preview sub, but i don't use PreviewImageToJpeg the way you do. i think that's where your problem is
2) if #1 works, then the timing loop is your problem. if #1 does not work, try to capture your preview just once, convert to a jpg and save it. see if you can load it in the image view that way. i'm not saying this is the solution for your app; but you need to know if you can at least capture the preview and save it to an image file. if you still can't see the image, then something else is going on.
i can only repeat that, except for the timing loop, i copied your code, ran it and generated a bitmap which i saw in an imageview. except for the timing loop, your code seems ok. that loop might give the device no time to breathe. expecially if you're using a big preview and a tight loop. a tiny preview might work.