New key on the keyboard

I work on开发者_JS百科 a iPhone project with iOS 4 and Xcode 4.

In a view I have several UITextField, that the user fills with numbers. So only the Numbers keyword is used.

When the user fills in a text field and click Go, some processing is started (modification of the text of several textFields).

Now I would like to consider also a second option: user open the keyboard but then decides to close it without any process (i.e. cancel the process).

So I need a keyboard with a cancel key as shown on this the picture:

Finally my question: how can I create a keyboard with a cancel key as above?

Edit: picture of my view

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The keyboard cannot be modified. You should add a cancel button, or some other way of triggering a cancel, in your UI.