简单的代码实现的炫酷navigationbar

动图

技术原理：

当你下拉scrollview的时候，会监听scrollview的contentOffset来调整头部背景图片的位置，通过CGAffineTransformMakeTranslation和CGAffineTransformScale实现头像的缩小。

具体代码实现：

-(void)willMoveToSuperview:(UIView *)newSuperview
{
    [self.scrollView addObserver:self forKeyPath:@"contentOffset" options:(NSKeyValueObservingOptionNew) context:Nil];
    self.scrollView.contentInset = UIEdgeInsetsMake(self.frame.size.height,  ,, );
    self.scrollView.scrollIndicatorInsets = self.scrollView.contentInset;
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    CGPoint newOffset = [change[@"new"] CGPointValue];
    [self updateSubViewsWithScrollOffset:newOffset];
}

-(void)updateSubViewsWithScrollOffset:(CGPoint)newOffset
{

    float destinaOffset = -;
    float startChangeOffset = -self.scrollView.contentInset.top;
    newOffset = CGPointMake(newOffset.x, newOffset.y<startChangeOffset?startChangeOffset:(newOffset.y>destinaOffset?destinaOffset:newOffset.y));

    float subviewOffset = self.frame.size.height-;
    float newY = -newOffset.y-self.scrollView.contentInset.top;
    float d = destinaOffset-startChangeOffset;
    float alpha = -(newOffset.y-startChangeOffset)/d;
    float imageReduce = -(newOffset.y-startChangeOffset)/(d*);
    self.subTitleLabel.alpha = alpha;
    self.titleLabel.alpha = alpha;
    self.frame = CGRectMake(, newY, self.frame.size.width, self.frame.size.height);
    self.backImageView.frame = CGRectMake(, -0.5*self.frame.size.height+(1.5*self.frame.size.height-)*(-alpha), self.backImageView.frame.size.width, self.backImageView.frame.size.height);

    CGAffineTransform t = CGAffineTransformMakeTranslation(,(subviewOffset-0.35*self.frame.size.height)*(-alpha));
    _headerImageView.transform = CGAffineTransformScale(t,
                                                        imageReduce, imageReduce);

    self.titleLabel.frame = CGRectMake(, 0.6*self.frame.size.height+(subviewOffset-0.45*self.frame.size.height)*(-alpha), self.frame.size.width, self.frame.size.height*0.2);
    self.subTitleLabel.frame = CGRectMake(, 0.75*self.frame.size.height+(subviewOffset-0.45*self.frame.size.height)*(-alpha), self.frame.size.width, self.frame.size.height*0.1);
}

Demo分享：

GitHub：https://github.com/ianisme/CoolNavi