On the Mac, you can always hit Command-Z to undo something. You can also hit Command-Shift-Z to redo something and put it back to what it was before you hit undo. Make sense?
This isn’t so easily done on iOS, as there isn’t a Command key, to being with, but there is, in fact, an option to undo and one to redo hidden in the iPad keyboard. Here’s how to get to each of them.
Grab an iPad and launch an app that does text input, like Notes. Tap into a text editing field and type something. Go ahead, be witty, you’ll feel good about yourself.
ONce you’ve typed something in, tap the “.?123″ button in the lower left corner of the keyboard, and you’ll see the undo option. Tap it to, well, undo whatever it is you just typed.
If you change your mind, and want to redo the typing, simply tap the “#+=” button, available only on the numbers and symbols keyboard layout, and you’ll see a redo button waiting for you. Tap it once to put back the witty stuff.
Now you know how to undo some typing, then redo it, using the on screen iPad keyboard. Of course, you can always just shake your iPad to undo, but that’s kind of impractical in some situations, right?
Via: OS X Daily