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[操作系统]iOS 下拉刷新


前言

讲下拉刷新及上拉加载之前先给大家解释UIScrollView的几个属性

  • contentSize是UIScrollView可以滚动的区域。
  • contentOfinset 苹果官方文档的解释是"内容视图嵌入到封闭的滚动视图的距离,我的理解是他实际上就是scrollView的Content View相对于scrollView的外壳的边距,他其实和CSS中的pading属性有点相似。
  • contentOffset是UIScrollView当前显示区域的顶点相对于frame顶点的偏移量,例如上面的例子如果拉到最下面,则contentOffset就是(0, 480),也就是y偏移了480.

下拉刷新及上拉加载原理

  • 下拉刷新实际上是监测UIScrollView的contentOffset的y值,当他往下拉动时,UIScrollView的contentOffset是一直减小的,然后把通过动画把它的contentInset值控制成一个定值,然后通过设置延时来把UIScrollView的contentInset的值恢复原点。啥话不说,上代码
//下拉刷新   if (scrollView.contentOffset.y < -100) {        [UIView animateWithDuration:1.0 animations:^{            self.scrollView.contentInset = UIEdgeInsetsMake(100, 0, 0, 0);          } completion:^(BOOL finished) {            NSLog(@"发起下拉刷新");            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{                [UIView animateWithDuration:1.0 animations:^{                    self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);        }];              });          }];    }

  • 上拉加载其实原理和下拉刷新基本是一样的,只不过判断的contentOffset的值不同,如果scrollView.bounds.size.height +  scrollView.contentOffset.y >scrollView.contentSize.height,说明你执行了上拉操作,然后实现起来基本就和下拉刷新是一样的。
//上拉加载    if (scrollView.bounds.size.height + scrollView.contentOffset.y >scrollView.contentSize.height) {        [UIView animateWithDuration:1.0 animations:^{            self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 50, 0);          } completion:^(BOOL finished) {            NSLog(@"发起上拉加载");            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{                [UIView animateWithDuration:1.0 animations:^{                    self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);                  }];      });    }];          }

下面奉上完整的demo代码,大家看不懂的可以私聊我,要是想深入了解的话可以去github搜索MJRefresh看完整的别人封装好的第三方

#import "ViewController.h"@interface ViewController ()<UIScrollViewDelegate>@property (nonatomic, strong) UIScrollView * scrollView;@end@implementation ViewController- (UIScrollView *)scrollView {    if (!_scrollView) {    _scrollView = [[UIScrollView alloc] initWithFrame:self.view.bounds];        //contentSize是可滑动的区域    _scrollView.contentSize = CGSizeMake(0, 900);    _scrollView.backgroundColor = [UIColor grayColor];    _scrollView.delegate = self;        //greenView实际上就是UIScrollView的content View    UIView * greenView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, 900)];    greenView.backgroundColor = [UIColor greenColor];    [_scrollView addSubview:greenView];      }  return _scrollView;}- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView {      //下拉刷新-当下拉刷新时,contentOffset实际上就是greenView相对于屏幕左上角的偏移量。  if (scrollView.contentOffset.y < -100) {        [UIView animateWithDuration:1.0 animations:^{            self.scrollView.contentInset = UIEdgeInsetsMake(100, 0, 0, 0);          } completion:^(BOOL finished) {            NSLog(@"发起下拉刷新");            //设置延时时间为2秒      dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{                [UIView animateWithDuration:1.0 animations:^{          //恢复之前的contentInset,让greenView回到原来的地方          self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);        }];              });          }];    }    //上拉加载    if (scrollView.bounds.size.height + scrollView.contentOffset.y >scrollView.contentSize.height) {        [UIView animateWithDuration:1.0 animations:^{            self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 50, 0);          } completion:^(BOOL finished) {            NSLog(@"发起上拉加载");            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{                [UIView animateWithDuration:1.0 animations:^{                    self.scrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 0);                  }];      });    }];          }  }- (void)viewDidLoad {  [super viewDidLoad];  // Do any additional setup after loading the view, typically from a nib.  [self.view addSubview:self.scrollView];      }- (void)didReceiveMemoryWarning {  [super didReceiveMemoryWarning];  // Dispose of any resources that can be recreated.}@end