Programmatically change UITextField Keyboard type

It's worth noting that if you want a currently-focused field to update the keyboard type immediately, there's one extra step:

// textField is set to a UIKeyboardType other than UIKeyboardTypeEmailAddress

[textField setKeyboardType:UIKeyboardTypeEmailAddress];
[textField reloadInputViews];

Without the call to reloadInputViews, the keyboard will not change until the selected field (the first responder) loses and regains focus.

A full list of the UIKeyboardType values can be found here, or:

typedef enum : NSInteger {
    UIKeyboardTypeDefault,
    UIKeyboardTypeASCIICapable,
    UIKeyboardTypeNumbersAndPunctuation,
    UIKeyboardTypeURL,
    UIKeyboardTypeNumberPad,
    UIKeyboardTypePhonePad,
    UIKeyboardTypeNamePhonePad,
    UIKeyboardTypeEmailAddress,
    UIKeyboardTypeDecimalPad,
    UIKeyboardTypeTwitter,
    UIKeyboardTypeWebSearch,
    UIKeyboardTypeAlphabet = UIKeyboardTypeASCIICapable
} UIKeyboardType;

There is a keyboardType property for a UITextField:

typedef enum {
    UIKeyboardTypeDefault,                // Default type for the current input method.
    UIKeyboardTypeASCIICapable,           // Displays a keyboard which can enter ASCII characters, non-ASCII keyboards remain active
    UIKeyboardTypeNumbersAndPunctuation,  // Numbers and assorted punctuation.
    UIKeyboardTypeURL,                    // A type optimized for URL entry (shows . / .com prominently).
    UIKeyboardTypeNumberPad,              // A number pad (0-9). Suitable for PIN entry.
    UIKeyboardTypePhonePad,               // A phone pad (1-9, *, 0, #, with letters under the numbers).
    UIKeyboardTypeNamePhonePad,           // A type optimized for entering a person's name or phone number.
    UIKeyboardTypeEmailAddress,           // A type optimized for multiple email address entry (shows space @ . prominently).
    UIKeyboardTypeDecimalPad,             // A number pad including a decimal point
    UIKeyboardTypeTwitter,                // Optimized for entering Twitter messages (shows # and @)
    UIKeyboardTypeWebSearch,              // Optimized for URL and search term entry (shows space and .)

    UIKeyboardTypeAlphabet = UIKeyboardTypeASCIICapable, // Deprecated

} UIKeyboardType;

Your code should read

if(user is prompted for numeric input only)
    [textField setKeyboardType:UIKeyboardTypeNumberPad];

if(user is prompted for alphanumeric input)
    [textField setKeyboardType:UIKeyboardTypeDefault];