Delegate that handles all the annoying gotchas of textfields

TextFieldDelegate.h

// As see on: http://cocoawithlove.com/2008/10/sliding-uitextfields-around-to-avoid.html

#import <Foundation/Foundation.h>

static const CGFloat KEYBOARD_ANIMATION_DURATION = 0.3;
static const CGFloat MINIMUM_SCROLL_FRACTION = 0.2;
static const CGFloat MAXIMUM_SCROLL_FRACTION = 0.8;
static const CGFloat PORTRAIT_KEYBOARD_HEIGHT = 216;
static const CGFloat LANDSCAPE_KEYBOARD_HEIGHT = 162;

@interface TextFieldDelegate : NSObject <UITextFieldDelegate> {
	UIView *view;
	CGFloat animatedDistance;
}

@property (retain, nonatomic) UIView *view;

- (TextFieldDelegate*) initWithView:(UIView*) _view;

@end

TextFieldDelegate.m

// as seen on: http://cocoawithlove.com/2008/10/sliding-uitextfields-around-to-avoid.html

#import "TextFieldDelegate.h"


@implementation TextFieldDelegate
@synthesize view;

- (TextFieldDelegate*) initWithView:(UIView*) _view {
	if (self = [super init]) {
		self.view = _view;
	}
	return self;
}

- (void) textFieldDidBeginEditing:(UITextField *)textField {
	
	// Get the rects of the text field being edited and the view that we're going to scroll. 
	// We convert everything to window coordinates, since they're not necessarily in the same 
	// coordinate space.
	CGRect textFieldRect = [self.view.window convertRect:textField.bounds fromView:textField];
	CGRect viewRect = [self.view.window convertRect:self.view.bounds fromView:self.view];
	
	// So now we have the bounds, we need to calculate the fraction between the top and bottom of 
	// the middle section for the text field's midline:
	CGFloat midline = textFieldRect.origin.y + 0.5 * textFieldRect.size.height;
	CGFloat numerator = midline - viewRect.origin.y - MINIMUM_SCROLL_FRACTION * viewRect.size.height;
    CGFloat denominator = (MAXIMUM_SCROLL_FRACTION - MINIMUM_SCROLL_FRACTION) * viewRect.size.height;
    CGFloat heightFraction = numerator / denominator;
	
	// Clamp this fraction so that the top section is all "0.0" and the bottom section is all "1.0".
	if (heightFraction < 0.0)
    {
        heightFraction = 0.0;
    }
    else if (heightFraction > 1.0)
    {
        heightFraction = 1.0;
    }
	
	// Now take this fraction and convert it into an amount to scroll by multiplying by the keyboard height
	// for the current screen orientation. Notice the calls to floor so that we only scroll by whole pixel amounts.
	UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
    if (orientation == UIInterfaceOrientationPortrait ||
        orientation == UIInterfaceOrientationPortraitUpsideDown) {
        animatedDistance = floor(PORTRAIT_KEYBOARD_HEIGHT * heightFraction);
    }
    else {
        animatedDistance = floor(LANDSCAPE_KEYBOARD_HEIGHT * heightFraction);
    }
	
	// Finally, apply the animation. Note the use of setAnimationBeginsFromCurrentState: 
	// — this will allow a smooth transition to new text field if the user taps on another.
	CGRect viewFrame = self.view.frame;
    viewFrame.origin.y -= animatedDistance;
    
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [UIView setAnimationDuration:KEYBOARD_ANIMATION_DURATION];
    
    [self.view setFrame:viewFrame];
    
    [UIView commitAnimations];
}

- (void) textFieldDidEndEditing:(UITextField *)textField {
	CGRect viewFrame = self.view.frame;
    viewFrame.origin.y += animatedDistance;
    
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [UIView setAnimationDuration:KEYBOARD_ANIMATION_DURATION];
    
    [self.view setFrame:viewFrame];
    
    [UIView commitAnimations];
}

- (BOOL) textFieldShouldReturn:(UITextField *)textField {
	[textField resignFirstResponder];
	return YES;
}

- (void) dealloc {
	[self.view release];
	[super dealloc];
}

@end