效果图：
滚动渐变NavBar.gif
在有UIScrollview的页面中，做一个NavBar 的渐变过渡，最好还是抽取出来。
使用方法,需要注意的是，恢复navbar的颜色最好是放在viewDidDisappear中，否则侧滑返回的时候，Navbar的颜色会出现问题。渐变的处理，就是把UIScrollview传给工具类即可：
-(void)viewDidDisappear:(BOOL)animated{
[super viewDidDisappear:animated];
[LXGradientNavManager resStoreToDefaultNavigationBar];
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
[self setUp];
[LXGradientNavManager managerWithController:self];
[LXGradientNavManager setOrignColor:[UIColor clearColor]];
[LXGradientNavManager setZeroAlphaOffset:0];
[LXGradientNavManager setFullAlphaOffset:self.tableView.tableHeaderView.height];
[LXGradientNavManager setDefaultColor:[UIColor hexStringToColor:@"F9F9F9"]];
}
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
[LXGradientNavManager dealGradientWithScrollView:scrollView];
}
工具类如下：
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@interface LXGradientNavManager : NSObject
@property(nonatomic,strong)UIColor *defaultColor; //默认的Nav的颜色
@property(nonatomic,strong)UIColor *orignColor; //最开始的颜色
@property(nonatomic,assign)float zeroAlphaOffset;
@property (nonatomic, assign) float fullAlphaOffset;
+(void)setOrignColor:(UIColor *)color;
+ (void)setDefaultColor:(UIColor *)color;
+ (void)setZeroAlphaOffset:(float)offset;
+ (void)setFullAlphaOffset:(float)offset;
+(void)managerWithController:(UIViewController *)viewController;
+(void)dealGradientWithScrollView:(UIScrollView *)scrollView;
+(void)reStoreToSystemNavigationBar; //change the navigationBar to system style
+(void)resStoreToDefaultNavigationBar; //恢复到默认的navbar
@end
#import "LXGradientNavManager.h"
@interface LXGradientNavManager()
@property (nonatomic, strong) UINavigationBar *selfNavigationBar;
@property (nonatomic, strong) UINavigationController *selfNavigationController;
@end
@implementation LXGradientNavManager
+(LXGradientNavManager *)sharedManager{
static LXGradientNavManager *manager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
manager = [[LXGradientNavManager alloc]init];
});
return manager;
}
+(void)managerWithController:(UIViewController *)viewController{
if (viewController.navigationController) {
UINavigationBar *navigationBar = viewController.navigationController.navigationBar;
[self sharedManager].selfNavigationBar = navigationBar;
[self sharedManager].selfNavigationController = viewController.navigationController;
[navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
[navigationBar setShadowImage:[UIImage new]];
}
}
+(void)dealGradientWithScrollView:(UIScrollView *)scrollView{
CGFloat y = scrollView.contentOffset.y;
UIColor *defaultColor = [self sharedManager].defaultColor;
if (y > [self sharedManager].fullAlphaOffset) {
UIImage *image =[self imageWithColor:defaultColor];
[[self sharedManager].selfNavigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];
}else{
CGFloat alpha = y /[self sharedManager].fullAlphaOffset;
UIImage *image =[self imageWithColor: [defaultColor colorWithAlphaComponent:alpha]];
[[self sharedManager].selfNavigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];
}
}
+ (void)reStoreToSystemNavigationBar {
[[self sharedManager].selfNavigationController setValue:[UINavigationBar new] forKey:@"navigationBar"];
}
+ (void)resStoreToDefaultNavigationBar{
UIImage *image =[self imageWithColor:[self sharedManager].defaultColor];
[[self sharedManager].selfNavigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];
}
+(void)setZeroAlphaOffset:(float)offset{
[self sharedManager].zeroAlphaOffset = offset;
}
+(void)setFullAlphaOffset:(float)offset{
[self sharedManager].fullAlphaOffset = offset;
}
+(void)setDefaultColor:(UIColor *)color{
[self sharedManager].defaultColor = color;
}
+(void)setOrignColor:(UIColor *)color{
[self sharedManager].orignColor = color;
[[self sharedManager].selfNavigationBar setBackgroundImage:[self imageWithColor:color] forBarMetrics:UIBarMetricsDefault];
}
+ (UIImage *)imageWithColor:(UIColor *)color {
CGRect rect = CGRectMake(0, 0, 1, 1);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[color setFill];
CGContextFillRect(context, rect);
UIImage *imgae = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return imgae;
}
关于 UIScrollview的起始偏移量，最好还是处理如下。
self.view.backgroundColor =[UIColor whiteColor];
self.extendedLayoutIncludesOpaqueBars = YES;
self.automaticallyAdjustsScrollViewInsets = NO;
会保证起始点不会偏移。
demo地址：滚动渐变NavBar
