目标：
向上移动控制器时候，出现NavigationBar
一开始是隐藏NavigationBar的
如果直接隐藏，然后再上移动出现navigationBar上部会出现一个_UIBackDropView，正是它决定了navigationBar的背景色。
实现：我们使用associatedObject将overlayView动态地绑定到UINavigationBar的instance上，当调用lt_setBackgroundColor的时候，我们只要更新这个overlayView就行啦～
#import <UIKit/UIKit.h>
@interface UINavigationBar (Awesome)
- (void)lt_setBackgroundColor:(UIColor *)backgroundColor;
@end
#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;
}
控制器中需要调用方法，这里实现控制器为tableView控制器
//
// YSBTHomeViewController.m
// YSBanTang
//
// Created by Evan on 16/7/1.
// Copyright © 2016年 Evan. All rights reserved.
//
#define NAVBAR_CHANGE_POINT 44
#import "YSBTHomeViewController.h"
static NSString * const YSBTHomeTableViewCellID = @"YSBTHomeTableViewCellID";
@interface YSBTHomeViewController ()<UITableViewDelegate,UITableViewDataSource>
@property (nonatomic, weak) UITableView *tableView;
@end
@implementation YSBTHomeViewController
#pragma mark - Datas
- (UITableView *)tableView
{
if (!_tableView)
{
UITableView *tableView = [[UITableView alloc] init];
tableView.frame = self.view.frame;
[tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:YSBTHomeTableViewCellID];
self.tableView = tableView;
[self.view addSubview:tableView];
}
return _tableView;
}
#pragma mark - Controls
#pragma mark - Initalize
#pragma mark - Lifecycle
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
[self setupNavigation];
[self setupContentContraints];
[self.tableView setupDataSourceDelegate:self]; //tableView分类
}
#pragma mark - Layout
- (void)setupNavigation
{
[self.navigationController.navigationBar setShadowImage:[UIImage new]];
[self.navigationController.navigationBar lt_setBackgroundColor:[UIColor clearColor]];
}
#pragma mark - UITableView DataSource && Delegate
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return 100;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:YSBTHomeTableViewCellID forIndexPath:indexPath];
cell.textLabel.text = @"111";
return cell;
}
#pragma mark - UIScrollView Delegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
UIColor * color = [UIColor colorWithPatternImage:[UIImage rx_captureImageWithImageName:@"nav_backgroud"]];
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]];
}
}
@end
完整代码：https://github.com/ltebean/LTNavigationBar