为UIKeyboardTypeNumberPad增加自定义按键

If you have ever written an iPhone app that requires numeric input,then you surely know about the UIKeyboardTypeNumberPad. And if you haveever used that flavor of the iPhone's keyboard, then you sur

ely knowthat it lacks one very important feature: The UIKeyboardTypeNumberPaddoes not have a "return" key.
In fact every other keyboard type (except for the pretty similarUIKeyboardTypePhonePad) does offer the possibility to be dismissed bysetting the returnKeyType property of the correspondingUITextInputTraits implementor. So how does one achieve the same effectwith the number pad? We have found a workround!
When looking at the number pad, you'll notice that there is anunused space on its bottom left. That's where we are going to plug inour custom "return" key.

To make it short: take a screenshot, cut out the whole backspacekey, flip it horizotally, clear its backspace symbol in Photoshop andoverlay it with the text that we want on our “return” key. We’ve chosento label it “DONE”. Now we have the image for our custombutton’s UIControlStateNormal. Repeat the whole procedure (with atouched backspace key when taking the screenshot) to get a second imagefor our button’s UIControlStateHighlighted. Here’s the result:
   
Now back to coding. First we need to know when the number pad isgoing to be slided up on the screen so we can plug in our custom buttonbefore that happens. Luckily there’s a notification for exactly thatpurpose, and registering for it is as easy as:
 
[[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(keyboardWillShow:) 
                                             name:UIKeyboardWillShowNotification 
                                           object:nil];
 [/pre]Don't forget to remove the observer from the notification center in the appropriate place once you're done with the whole thing:
 
[[NSNotificationCenter defaultCenter] removeObserver:self];[/pre]Now we’re getting to the heart of it. All we have to do in thekeyboardWillShow method is to locate the keyboard view and add ourbutton to it. The keyboard view is part of a second UIWindow of ourapplication as others have already figured out (see this thread).So we take a reference to that window (it will be the second window inmost cases, so objectAtIndex:1 in the code below is fine), traverse itsview hierarchy until we find the keyboard and add the button to itslower left:
 
- (void)keyboardWillShow:(NSNotification *)note {  
    // create custom button
    UIButton *doneButton = [UIButton buttonWithType:UIButtonTypeCustom];
    doneButton.frame = CGRectMake(0, 163, 106, 53);
    doneButton.adjustsImageWhenHighlighted = NO;
    [doneButton setImage:[UIImage imageNamed:@"DoneUp.png"] forState:UIControlStateNormal];
    [doneButton setImage:[UIImage imageNamed:@"DoneDown.png"] forState:UIControlStateHighlighted];
    [doneButton addTarget:self action:@selector(doneButton:) forControlEvents:UIControlEventTouchUpInside];
 
    // locate keyboard view
    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];
    UIView* keyboard;
    for(int i=0; i<[tempWindow.subviews count]; i++) {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard view found; add the custom button to it
        if([[keyboard description] hasPrefix:@"<UIKeyboard"] == YES)
            [keyboard addSubview:doneButton];
    }
}[/pre]Voilà, that’s it! The empty space for our button starts atcoordinate (0, 163) and has the dimensions (106, 53). The doneButtonmethod has to be written now of course, but that’s not hard any more.Just make sure that you call resignFirstResponder on the text fieldthat is being edited to have the keyboard slide down.

原码下载地址：http://files.neoos.ch/KeyboardExtension.zip