http://stackoverflow.com/a/13614405/1798418

KeyBoardSizeView.h

@interface KeyBoardSizeView : UIView
@property (nonatomic,weak) NSLayoutConstraint* heightConstraint;
@end

KeyBoardSizeView.m

#import "KeyBoardSizeView.h"

@implementation KeyBoardSizeView

-(instancetype)initWithCoder:(NSCoder *)aDecoder{
    if(self = [super initWithCoder:aDecoder]){
        [self setUp];
    }
    return self;}

-(instancetype)initWithFrame:(CGRect)frame{
    if(self = [super initWithFrame:frame]){
        [self setUp];
    }
    return self;
}

-(instancetype)init{
    if(self = [super init]){
        [self setUp];
    }
    return self;
}
-(void)awakeFromNib{
    if(self.heightConstraint) return;
    
    for (NSLayoutConstraint* constraint in self.constraints) {
        if(constraint.firstAttribute == NSLayoutAttributeHeight){
            self.heightConstraint = constraint;
            break;
        }
    }
    
    [self checkHeightConstraint];
}
-(void)setUp{
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardChangeFrame:)
                                                 name:UIKeyboardWillShowNotification
                                               object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardChangeFrame:)
                                                 name:UIKeyboardWillHideNotification
                                               object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardChangeFrame:)
                                                 name:UIKeyboardWillChangeFrameNotification
                                               object:nil];
}

- (void) dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    // uncomment for non-ARC:
    // [super dealloc];
}
-(void)checkHeightConstraint{
    if (!self.heightConstraint) {
        @throw [NSException exceptionWithName:@"KeyBoardSizeView Exception" reason:@"height constraint isn't set" userInfo:nil];
    }
}

-(void)keyboardChangeFrame:(NSNotification*)notification{
    if(!self.superview) return;

    [self checkHeightConstraint];

    CGRect keyboardEndFrame;
    [[notification userInfo][UIKeyboardFrameEndUserInfoKey] getValue:&keyboardEndFrame];
    keyboardEndFrame = [self.superview convertRect:keyboardEndFrame toView:nil];
    UIViewAnimationCurve curve =[notification.userInfo[UIKeyboardAnimationCurveUserInfoKey] integerValue];
    NSTimeInterval duration = [notification.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    self.heightConstraint.constant = CGRectGetHeight(CGRectIntersection(self.superview.frame, keyboardEndFrame));
    [self setNeedsUpdateConstraints];
    [self setNeedsLayout];

    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:duration];
    [UIView setAnimationCurve:curve];
    [UIView setAnimationBeginsFromCurrentState:YES];
    
    [self.superview layoutIfNeeded];
    
    [UIView commitAnimations];
}

@end