iOS开发 - 渐变导航条升级版（判断滚动的方向和改变方向时的位置）

来源：互联网发布：中国2015gdp数据编辑：程序博客网时间：2024/05/16 09:42

博主以前发过一篇渐变导航条的，地址：http://blog.csdn.net/codingfire/article/details/51604098

但是在中部滚动的时候不能实现渐变，类似的好的效果在百度贴吧里出现过，所以博主对那个Demo进行了改进，看下效果：
这里写图片描述

这里加上了对向上向下和改变方向时的位置的判断,下面看下代码：

#import "ViewController.h"@interface ViewController ()<UIScrollViewDelegate,UITableViewDelegate,UITableViewDataSource>{    UIImageView *barImageView;    UITableView *myTableView;    float _lastPosition;    float currentPostion;    float stopPosition;}@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.    self.view.backgroundColor=[UIColor whiteColor];    //    [self.navigationController.navigationBar setBackgroundImage:[UIImage new]    //                                                  forBarMetrics:UIBarMetricsDefault];    //    self.navigationController.navigationBar.shadowImage = [UIImage new];    _lastPosition = 0;    stopPosition = 0;    [[NSUserDefaults standardUserDefaults]setObject:@"1" forKey:@"first"];    [[NSUserDefaults standardUserDefaults]synchronize];    self.navigationController.navigationBar.barTintColor=[UIColor orangeColor];    self.title=@"This is my title!";    self.navigationController.navigationBar.tintColor = [UIColor blackColor];    myTableView=[[UITableView alloc]initWithFrame:self.view.bounds];    myTableView.delegate=self;    myTableView.dataSource=self;    [self.view addSubview:myTableView];    UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 320, 270)];    imageView.image=[UIImage imageNamed:@"1.png"];    myTableView.tableHeaderView=imageView;    barImageView = self.navigationController.navigationBar.subviews.firstObject;    NSString *str=@"122222";}#pragma mark - UITableViewDelaget-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{    return 40;}-(CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath{    return 44;}-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{    UITableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:@"cell"];    if (!cell) {        cell=[[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];    }    cell.textLabel.text=[NSString stringWithFormat:@"%ld",indexPath.row];    return cell;}- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView{    [NSObject cancelPreviousPerformRequestsWithTarget:self];    stopPosition = currentPostion + 64;    NSLog(@"滑动停止:%f",stopPosition);}- (void)scrollViewDidScroll:(UIScrollView *)scrollView{    currentPostion = scrollView.contentOffset.y;    if (currentPostion > 0) {        if (currentPostion - _lastPosition >= 0) {            if ([[NSUserDefaults standardUserDefaults]objectForKey:@"first"]!=nil) {                [[NSUserDefaults standardUserDefaults]removeObjectForKey:@"first"];                [[NSUserDefaults standardUserDefaults]synchronize];//                [NSObject cancelPreviousPerformRequestsWithTarget:self];//                [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.00001];                [[NSUserDefaults standardUserDefaults]setObject:@"1" forKey:@"second"];                [[NSUserDefaults standardUserDefaults]synchronize];                stopPosition = currentPostion + 64;            }            _lastPosition = currentPostion;            NSLog(@"ScrollUp now    current:%f    last:%f    stop:%f",currentPostion,_lastPosition,stopPosition);            self.navigationController.navigationBar.alpha = 1 - currentPostion / 400;        }        else        {            if ([[NSUserDefaults standardUserDefaults]objectForKey:@"second"]!=nil) {                [[NSUserDefaults standardUserDefaults]removeObjectForKey:@"second"];                [[NSUserDefaults standardUserDefaults]synchronize];//                [NSObject cancelPreviousPerformRequestsWithTarget:self];//                [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.00001];                [[NSUserDefaults standardUserDefaults]setObject:@"1" forKey:@"first"];                [[NSUserDefaults standardUserDefaults]synchronize];                stopPosition = currentPostion + 64;            }            _lastPosition = currentPostion;            NSLog(@"ScrollDown now    current:%f   last:%f    stop:%f",currentPostion,_lastPosition,stopPosition);            self.navigationController.navigationBar.alpha = (stopPosition - currentPostion)/200;        }    }}

这里有一个关于滚动停止的判断，但是博主注释了代码，在下一篇博客中，会针对滚动停止，和改变方向，以及滚动未停止时改变方向的情况作说明。

代码很简单，需要Demo的点击下载：下载

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