大體思路：定義一個UINavigationBar的Category,在NavigationBar頂層增加一個檢視overlay。滾動時通過設定overlay檢視的背景色和透明度來達到隱藏和顯示導航欄效果。程式碼如下：

#import <UIKit/UIKit.h>

@interface UINavigationBar (CustomNavigationBar)

- (void)setCustomBackgroundColor:(UIColor *)backgroundColor;

@end

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

@implementation UINavigationBar (CustomNavigationBar)

static char overlayKey;

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

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

- (void)setCustomBackgroundColor:(UIColor *)backgroundColor
{
    if (!self.overlay) {
        [self setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
        [self setShadowImage:[UIImage new]];
        //需要遮住狀態列
        self.overlay = [[UIView alloc] initWithFrame:CGRectMake(0, -20, [UIScreen mainScreen].bounds.size.width, 64)];
        self.overlay.autoresizingMask = UIViewAutoresizingFlexibleWidth ;
        [self insertSubview:self.overlay atIndex:0];
    }
    self.overlay.backgroundColor = backgroundColor;
}
 

tableview滾動時，呼叫方法設定導航欄背景色：

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    UIColor *color = [UIColor blueColor];
    CGFloat offsetY = scrollView.contentOffset.y;
    if (offsetY > 0) {
        CGFloat alpha = 1- (64 - offsetY) / 64;
        [self.navigationController.navigationBar setCustomBackgroundColor:[color colorWithAlphaComponent:alpha]];
    } else {
        [self.navigationController.navigationBar setCustomBackgroundColor:[color colorWithAlphaComponent:0]];
    }
}