实在不知道怎么给这篇文章起一个比较好的名字，我们还是先看下效果吧

效果图

下面看实现，这边以设置tableView的headerView为例来讲解
老样子，直接上代码

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; min-height: 16.0px}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #1d9421}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #703daa}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #6122ae}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font-variant-ligatures: no-common-ligatures; color: #c32275}span.s3 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s4 {font: 14.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}span.s5 {font-variant-ligatures: no-common-ligatures; color: #294c50}span.s6 {font-variant-ligatures: no-common-ligatures; color: #6122ae}span.s7 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s8 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s9 {font-variant-ligatures: no-common-ligatures; color: #0435ff}span.s10 {font-variant-ligatures: no-common-ligatures; color: #78492a}span.s11 {font-variant-ligatures: no-common-ligatures; color: #c91b13}

- (void)setTableViewHeaderView {
    
    //将navigationBar的背景设为透明
    [self.navigationController.navigationBar lt_setBackgroundColor:[UIColor clearColor]];
    
    //去掉navigationBar下面的那条分割线
    [self.navigationController.navigationBar setShadowImage:[UIImage new]];

    CGFloat headerViewHeight = 200;
    
    UIView* headerView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH , headerViewHeight)];
    
    UIImageView* imgView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"123.jpg"]];
    //这个-64非常关键
    imgView.frame = CGRectMake(0, -64, SCREEN_WIDTH, headerViewHeight + 64);

    [headerView addSubview:imgView];

    self.tableView.tableHeaderView = headerView;
}

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #822e0e}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #1d9421}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #703daa}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font: 14.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #c32275}span.s4 {font-variant-ligatures: no-common-ligatures; color: #6122ae}span.s5 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s6 {font-variant-ligatures: no-common-ligatures; color: #0435ff}span.s7 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s8 {font-variant-ligatures: no-common-ligatures; color: #78492a}span.s9 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s10 {font-variant-ligatures: no-common-ligatures; color: #294c50}

#pragma mark -  UIScrollViewDelegate
//实现UIScrollView的代理方法以实现navigationBar滚动时颜色变化
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    UIColor * color = [UIColor colorWithRed:0 green:175/255.0 blue:240/255.0 alpha:1];
    CGFloat offsetY = scrollView.contentOffset.y;
    if (offsetY > NAVBAR_CHANGE_POINT) {
        CGFloat alpha = MIN(1, 1 - ((NAVBAR_CHANGE_POINT + 64 - offsetY) / 64));
        [self.navigationController.navigationBar lt_setBackgroundColor:[color colorWithAlphaComponent:alpha]];
    } else {
        [self.navigationController.navigationBar lt_setBackgroundColor:[color colorWithAlphaComponent:0]];
    }
}

** 原理 **
设置tableView的headerView

当我们给定一个view给tableView的headerView时候，这个view的y值会自动被放置到navigationBar的下面

但是，我们再在这个view上添加一个view，如上面代码中 [headerView addSubview:imgView]

然后将imgView.frame = CGRectMake(0, -64, SCREEN_WIDTH, headerViewHeight + 64);

这个frame的y值设为-64，刚好超出navigationBar和statusBar
而navigationBar我们又设成了透明的，statusBar又在view的上方，这样就巧妙的实现了例子gif图中的效果

下面粘一个github上看到的一个navigationBar的分类，写的很漂亮
** .h 文件 **

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #1d9421}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; min-height: 16.0px}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #c91b13}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #c32275}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font: 14.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #822e0e}span.s4 {font-variant-ligatures: no-common-ligatures; color: #c32275}span.s5 {font-variant-ligatures: no-common-ligatures; color: #6122ae}span.s6 {font-variant-ligatures: no-common-ligatures; color: #703daa}

/**
 *  快速方便设置navigation bar
 */

#import <UIKit/UIKit.h>

@interface UINavigationBar (Awesome)
- (void)lt_setBackgroundColor:(UIColor *)backgroundColor;
- (void)lt_setElementsAlpha:(CGFloat)alpha;
- (void)lt_setTranslationY:(CGFloat)translationY;
- (void)lt_reset;
@end

** .m 文件 **

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #c91b13}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; min-height: 16.0px}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #3d1d81}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #703daa}p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #1d9421}p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Menlo; color: #c32275}span.s1 {font-variant-ligatures: no-common-ligatures; color: #822e0e}span.s2 {font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #c32275}span.s4 {font-variant-ligatures: no-common-ligatures; color: #6122ae}span.s5 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s6 {font-variant-ligatures: no-common-ligatures; color: #539aa4}span.s7 {font-variant-ligatures: no-common-ligatures; color: #294c50}span.s8 {font-variant-ligatures: no-common-ligatures; color: #0435ff}span.s9 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s10 {font-variant-ligatures: no-common-ligatures; color: #c91b13}span.s11 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}

#import "UINavigationBar+Awesome.h"
#import <objc/runtime.h>

@implementation UINavigationBar (Awesome)
static char overlayKey;

- (UIView *)overlay
{
    return objc_getAssociatedObject(self, &overlayKey);
}

- (void)setOverlay:(UIView *)overlay
{
    objc_setAssociatedObject(self, &overlayKey, overlay, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)lt_setBackgroundColor:(UIColor *)backgroundColor
{
    if (!self.overlay) {
        [self setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
        self.overlay = [[UIView alloc] initWithFrame:CGRectMake(0, -20, [UIScreen mainScreen].bounds.size.width, CGRectGetHeight(self.bounds) + 20)];
        self.overlay.userInteractionEnabled = NO;
        self.overlay.autoresizingMask = UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;
        [self insertSubview:self.overlay atIndex:0];
    }
    self.overlay.backgroundColor = backgroundColor;
}

- (void)lt_setTranslationY:(CGFloat)translationY
{
    self.transform = CGAffineTransformMakeTranslation(0, translationY);
}

- (void)lt_setElementsAlpha:(CGFloat)alpha
{
    [[self valueForKey:@"_leftViews"] enumerateObjectsUsingBlock:^(UIView *view, NSUInteger i, BOOL *stop) {
        view.alpha = alpha;
    }];
    
    [[self valueForKey:@"_rightViews"] enumerateObjectsUsingBlock:^(UIView *view, NSUInteger i, BOOL *stop) {
        view.alpha = alpha;
    }];
    
    UIView *titleView = [self valueForKey:@"_titleView"];
    titleView.alpha = alpha;
//    when viewController first load, the titleView maybe nil
    [[self subviews] enumerateObjectsUsingBlock:^(UIView *obj, NSUInteger idx, BOOL *stop) {
        if ([obj isKindOfClass:NSClassFromString(@"UINavigationItemView")]) {
            obj.alpha = alpha;
            *stop = YES;
        }
    }];
}

- (void)lt_reset
{
    [self setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];
    [self.overlay removeFromSuperview];
    self.overlay = nil;
}

@end

希望会对大家有帮助O(∩_∩)O！！！