ios开发图片轮播器以及定时器小问题

时间：2021-01-18 00:10:07

一：图片轮播器效果如图:能实现自动轮播，到最后一页时，轮播回来，可以实现拖拽滚动

ios开发图片轮播器以及定时器小问题

 

二：代码：

  1 #import "ViewController.h"
  2 static CGFloat const imageCount = 5;
  3 @interface ViewController ()<UIScrollViewDelegate>
  4 /*scrollView*/
  5 @property (nonatomic,weak)UIScrollView *scroll;
  6 /*pageControl*/
  7 @property (nonatomic,weak)UIPageControl *pageControl;
  8 /*timer*/
  9 @property (nonatomic ,strong)NSTimer *timer;
 10 @property (nonatomic,assign)int  a;
 11 @end
 12 
 13 @implementation ViewController
 14 
 15 - (void)viewDidLoad {
 16     [super viewDidLoad];
 17     
 18     //0:创建底部视图
 19     UIView *bottomView = [[UIView alloc]init];
 20     bottomView.frame = CGRectMake(20, 100, self.view.frame.size.width - 40, 200);
 21     [self.view addSubview:bottomView];
 22     
 23     
 24     //1:创建滚动视图
 25     UIScrollView *scrollView = [[UIScrollView alloc]init];
 26     scrollView.frame  = bottomView.bounds;
 27     scrollView.bounces = NO;
 28     scrollView.showsVerticalScrollIndicator = NO;
 29     scrollView.showsHorizontalScrollIndicator = NO;
 30     scrollView.pagingEnabled = YES;
 31     scrollView.delegate = self;
 32     scrollView.backgroundColor = [UIColor redColor];
 33     self.scroll = scrollView;
 34     [bottomView addSubview:scrollView];
 35     
 36     //2:创建ImageView
 37     CGFloat imageWidth = scrollView.frame.size.width;
 38     CGFloat imageHeight = scrollView.frame.size.height;
 39     
 40     for (int i = 0; i < imageCount; i++) {
 41         
 42         UIImageView *imageView = [[UIImageView alloc]init];
 43         imageView.frame = CGRectMake(i *imageWidth, 0, imageWidth, imageHeight);
 44         imageView.image = [UIImage imageNamed:[NSString stringWithFormat:@"img_0%d.png",i+1]];
 45         [scrollView addSubview:imageView];
 46         
 47     }
 48     
 49     //3:设置scroll的contentSize
 50     scrollView.contentSize = CGSizeMake(imageCount *imageWidth, 0);
 51     
 52     
 53     //4:创建pageControl
 54     UIPageControl *pageControl = [[UIPageControl alloc]init];
 55     pageControl.numberOfPages = imageCount;
 56     pageControl.currentPage = 0;
 57     pageControl.pageIndicatorTintColor = [UIColor whiteColor];
 58     pageControl.currentPageIndicatorTintColor = [UIColor redColor];
 59     pageControl.center = CGPointMake(bottomView.frame.size.width *0.5, bottomView.frame.size.height *0.9);
 60     self.pageControl = pageControl;
 61     [bottomView addSubview:pageControl];
 62     
 63     //5：添加定时器
 64     NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];
 65     NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
 66     /*
 67      forMode的参数：
 68      NSDefaultRunLoopMode
 69      NSRunLoopCommonModes
 70      */
 71     self.timer = timer;
 72     [runLoop addTimer:timer forMode: NSRunLoopCommonModes];
 73 //    [timer fire];
 74     
 75     
 76     //6:添加UITextView
 77     UITextView *textView = [[UITextView alloc]init];
 78     textView.frame = CGRectMake(0, 320, self.view.frame.size.width, 150);
 79     textView.text = @"凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo凡事看大佛我阿萨德fo一我啊搜ID念佛爱上你都放那艘IDif完加强覅进去我ijefo";
 80     textView.scrollEnabled = YES;
 81     textView.backgroundColor = [UIColor redColor];
 82     [self.view addSubview:textView];
 83 }
 84 
 85 - (void)changeImage {
 86     
 87     NSInteger page = self.pageControl.currentPage;
 88 
 89     
 90     
 91     if (page == imageCount -1) {
 92         self.a = imageCount -1;
 93     }
 94     
 95     
 96     if (page == 0) {
 97         self.a = 0;
 98     }
 99     
100 
101     if (self.a == imageCount -1) {
102         
103         page -- ;
104        
105     }else {
106         
107         page ++;
108     }
109     
110 
111 //    [self.scroll setContentOffset:CGPointMake(page *self.scroll.frame.size.width, 0) animated:YES];
112     [UIView animateWithDuration:1.0 animations:^{
113         self.scroll.contentOffset = CGPointMake(page *self.scroll.frame.size.width, 0);
114     }];
115     
116 }
117 
118 - (void)scrollViewDidScroll:(UIScrollView *)scrollView {
119     
120         //当下一页滑到>=0.5宽度时，此时就要改变pageControl
121         CGFloat page = scrollView.contentOffset.x / scrollView.frame.size.width;
122         NSUInteger currentPage = page;
123         self.pageControl.currentPage = (page - currentPage) < 0.5 ? currentPage : currentPage +1;
124 }
125 
126 //拖拽开始时关闭定时器，定时器一旦关闭，就不能再重新开启
127 - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
128     [self.timer invalidate];
129 
130 }
131 
132 - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
133     
134     self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];
135 }
136 
137 
138 @end

三：知识点总结

1：创建定时器： 1：NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];此方法创建的定时器，必须加到NSRunLoop中，NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; [runLoop addTimer:timer forMode: NSRunLoopCommonModes];第二个参数有两种类型可供选择： forMode的参数： NSDefaultRunLoopMode  NSRunLoopCommonModes，第一个参数为默认参数，当下面有textView，textfield等控件时，拖拽控件，此时轮播器会停止轮播，因为NSRunLoop的原因，NSRunLoop为一个死循环，实时监测有无事件响应，textView或是textField的事件会影响图片轮播，使用第二个参数会解决这个问题 2： self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];此种创建定时器的方式，默认加到了runloop，且默认为第二个参数。3：定时器方法：[timer fire];此时会立刻执行定时器的方法，若是没有调用此方法，则会等待2秒执行定时器的方法。

2：轮播器的拖拽：在拖拽轮播器时，不影响轮播效果，实现滚动代理的开始拖拽方法，并关闭定时器[self.timer invalidate];定时器一旦被关闭，则不能再重新开启，需要重新创建定时器。在拖拽结束的代理中，再重新创建定时器

3：图片滚动超过宽度的0.5时的计算方法：四舍五入CGFloat page = scrollView.contentOffset.x / scrollView.frame.size.width; NSUInteger currentPage = page; self.pageControl.currentPage = (page - currentPage) < 0.5 ? currentPage : currentPage +1;先求出滚动的浮点数，在转化成整数，做差值，小于0.5的取当前的整数，大于0.5的取当前整数加1

4：设置scrollView的偏移量：1：UIView的动画  2：[self.scroll setContentOffset:CGPointMake(page *self.scroll.frame.size.width, 0) animated:YES];第二种方法，滚动的时间很短，时间小于1秒，第一种就是可以控制动画的时间，和完成动画的回调

5：设置轮播效果：

    NSInteger page = self.pageControl.currentPage;

    if (page == imageCount -1) {

        self.a = imageCount -1;

    }

    if (page == 0) {

        self.a = 0;

    }

 

    if (self.a == imageCount -1) {

        

        page -- ;

       

    }else {

        

        page ++;

    }

注意：不要在此方法中，设置pageControl的currentPage，因为如果设置了，会立刻偏移到相应的位置，但是此时还在实时监测scrollView的滚动，在此滚动代理中，小于宽度一半时，会取当前的整数页，大于时会取整数+1页，所以此时pageControl会立刻到某页，在回到-1页，再突然回到某页，存在bug。不要设置pageControl的currentPage，让其直接在滚动代理中去设置。

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