ios開發圖片輪播器以及定時器小問題

一：圖片輪播器效果如圖:能實現自動輪播，到最後一頁時，輪播回來，能夠實現拖拽滾動

 

二：代碼：

  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:建立底部視圖
 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:建立滾動視圖
 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:建立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:設置scroll的contentSize
 50     scrollView.contentSize = CGSizeMake(imageCount *imageWidth, 0);
 51     
 52     
 53     //4:建立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：添加定時器
 64     NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];
 65     NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
 66     /*
 67      forMode的參數：
 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 = @"凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我ijefo凡事看大佛我阿薩德fo一我啊搜ID唸佛愛上你都放那艘IDif完增強覅進去我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         //當下一頁滑到>=0.5寬度時，此時就要改變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 //拖拽開始時關閉定時器，定時器一旦關閉，就不能再從新開啓
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：知識點總結

1：建立定時器： 1：NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];此方法建立的定時器，必須加到NSRunLoop中，NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; [runLoop addTimer:timer forMode: NSRunLoopCommonModes];第二個參數有兩種類型可供選擇： forMode的參數： NSDefaultRunLoopMode  NSRunLoopCommonModes，第一個參數爲默認參數，當下面有textView，textfield等控件時，拖拽控件，此時輪播器會中止輪播，由於NSRunLoop的緣由，NSRunLoop爲一個死循環，實時監測有無事件響應，textView或是textField的事件會影響圖片輪播，使用第二個參數會解決這個問題 2： self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(changeImage) userInfo:nil repeats:YES];此種建立定時器的方式，默認加到了runloop，且默認爲第二個參數。3：定時器方法：[timer fire];此時會馬上執行定時器的方法，如果沒有調用此方法，則會等待2秒執行定時器的方法。

2：輪播器的拖拽：在拖拽輪播器時，不影響輪播效果，實現滾動代理的開始拖拽方法，並關閉定時器[self.timer invalidate];定時器一旦被關閉，則不能再從新開啓，須要從新建立定時器。在拖拽結束的代理中，再從新建立定時器

3：圖片滾動超過寬度的0.5時的計算方法：四捨五入CGFloat page = scrollView.contentOffset.x / scrollView.frame.size.width; NSUInteger currentPage = page; self.pageControl.currentPage = (page - currentPage) < 0.5 ? currentPage : currentPage +1;先求出滾動的浮點數，在轉化成整數，作差值，小於0.5的取當前的整數，大於0.5的取當前整數加1

4：設置scrollView的偏移量：1：UIView的動畫  2：[self.scroll setContentOffset:CGPointMake(page *self.scroll.frame.size.width, 0) animated:YES];第二種方法，滾動的時間很短，時間小於1秒，第一種就是能夠控制動畫的時間，和完成動畫的回調

5：設置輪播效果：

    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，設置pageControl的currentPage，由於若是設置了，會馬上偏移到相應的位置，可是此時還在實時監測scrollView的滾動，在此滾動代理中，小於寬度一半時，會取當前的整數頁，大於時會取整數+1頁，因此此時pageControl會馬上到某頁，在回到-1頁，再忽然回到某頁，存在bug。不要設置pageControl的currentPage，讓其直接在滾動代理中去設置。