如何使用Objective C以2秒的间隔一张一张地自动滚动图像？

Posted 2023-03-16

【中文标题】如何使用Objective C以2秒的间隔一张一张地自动滚动图像？

【英文标题】：How to autoscroll images one by one by the interval of 2 seconds, using Objective C?

【发布时间】：2017-02-04 07:22:27

【问题描述】：

我已经为少数图像集合制作了滚动视图，我希望它以 2 秒的间隔一张一张地自动滚动图像。通过下面的代码，我可以让所有图像一次滑动，但我希望一个图像在时间上滚动，然后另一个图像。

-(void)scrollPages

UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0,0, self.view.frame.size.width, self.view.frame.size.height)];
scrollView.contentSize = CGSizeMake(320, 465);

[scrollView setScrollEnabled:YES];
[scrollView setPagingEnabled:YES];
[scrollView setAlwaysBounceVertical:NO];
[self.uiSubView addSubview:scrollView];

NSMutableArray *arrImage = [NSMutableArray arrayWithObjects:@"a.jpeg", @"cat.jpg", @"s.jpeg",@"ss.jpeg", nil];

for (int i = 0; i < [arrImage count]; i++)

    CGFloat xOrigin = i * scrollView.frame.size.width;


    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(xOrigin, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
    [imageView setImage:[UIImage imageNamed:[arrImage objectAtIndex:i]]];
    [imageView setContentMode:  UIViewContentModeScaleAspectFit];

    [scrollView addSubview:imageView];




[scrollView setContentSize:CGSizeMake(scrollView.frame.size.width * [arrImage count], scrollView.frame.size.height)];



CGFloat currentOffset = scrollView.contentOffset.x;

if(currentOffset < 2500)

    CGFloat newOffset = currentOffset + 1250;



    [UIScrollView beginAnimations:nil context:NULL];
    [UIScrollView setAnimationDuration:3];
    [scrollView setContentOffset:CGPointMake(newOffset,0.0) animated:YES];
    

【参考方案1】：

尝试使用 dispatch_after 函数进行简单递归。 像这样的：

-(void)scrollToNextImage
    //place here code for computing and setting scrollview offset

    _weak typeof(self) weakSelf = self;  //for avoiding retain cycle
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^
        [weakSelf scrollToNextImage];
    );

请注意，在这种情况下，即使视图控制器消失，图像也会滚动。递归只会在关闭视图控制器后结束。如果你不想要这样的行为，你可以添加额外的条件来检查 viewcontroller 在调度下一个滚动之前是否可见 - 你可以在这里检查如何做他：How to tell if UIViewController's view is visible