UIScrollView 的自动滚动

Question

我使用 setContentOffset 方法自动滚动到特定点，无需用户交互。

[menuScrollView setContentOffset:CGPointMake(600.0,0) animated:YES]

但是当我尝试以循环方式调用相同的方法以减慢滚动速度时，滚动永远不会发生

for (int i = 1; i<=30; i++) {
        [menuScrollView setContentOffset:CGPointMake(600.0-i*10,0.0) animated:YES];
        NSLog(@"%f",600.0-i*10);        
    }

在上面这段代码中，UIScrollview 的滚动只发生了一次（第一次迭代（并且它不会在剩余的 29 次迭代中滚动。这里有什么问题？

Answer 1

我认为当它处于这样的循环中时，用户界面不会更新。

尝试使用 NSTimer 而不是像这样将其置于紧密循环中。

scrollTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(scrollView) userInfo:nil repeats:YES];

- (void) scrollView {
    CGFloat currentOffset = menuScrollView.contentOffset.x;
    CGFloat newOffset = currentOffset - 10;
    [menuScrollView setContentOffset:CGPointMake(newOffset,0.0) animated:YES];
}

注意：这是我的想法，所以我不保证它会起作用。

Answer 2

这里是自动滚动UIScrollView的代码：-

    ![CGFloat cx1;
    int h=0;
    int z=0;
    int x=1;
    bool isdragging=false;


- (void)setupHorizontalScrollView : (UIScrollView *)scrollView
{

    if (arrTopFive.count == 0) {
        return;
    }

    for(UIView *subview in \[scrollView subviews\]) {
        \[subview removeFromSuperview\];
    }

    scrollView.delegate = self;

    \[scrollView setBackgroundColor:\[UIColor clearColor\]\];
    \[scrollView setCanCancelContentTouches:NO\];

//    scrollView.indicatorStyle = UIScrollViewIndicatorStyleWhite;
    scrollView.clipsToBounds = NO;
    scrollView.scrollEnabled = YES;




    CGFloat cx = 0;
    for (int i = 0;i<arrTopFive.count;i++)
    {

        clsShows *c=\[arrTopFive objectAtIndex:i\];

        UIImageView *imageView = \[\[UIImageView alloc\] init\];
        imageView.userInteractionEnabled=YES;

        UITapGestureRecognizer *tapGesture = \[\[UITapGestureRecognizer alloc\] initWithTarget:self action:@selector(tvShowTopFiveClicked:)\];
        tapGesture.numberOfTapsRequired = 1;
        \[imageView addGestureRecognizer:tapGesture\];
        imageView.tag=i;

        \[imageView sd_setImageWithURL:\[NSURL URLWithString:c.imageurl\] placeholderImage:\[UIImage imageNamed:@"img_placeholder.jpg"\]\];

        CGRect rect = imageView.frame;
        rect.size.height = 250;
        rect.size.width = 500;
        rect.origin.x = cx;
        rect.origin.y = 0;

        imageView.frame = rect;

        \[scrollView addSubview:imageView\];

        cx += imageView.frame.size.width+5;

    }

    \[scrollView setContentSize:CGSizeMake(cx, \[scrollView bounds\].size.height)\];
    cx1=cx-\[scrollView bounds\].size.width;


    \[NSTimer scheduledTimerWithTimeInterval:.1 target:self selector:@selector(onTimer) userInfo:nil repeats:YES\];
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    if (scrollView.dragging) {
        isdragging=true;
        h=ceil((float)scrollView.contentOffset.x / 5) * 5;
        z=ceil((float)scrollView.contentOffset.x / 5) * 5;
        if (h<0) {
            h=0;
            z=0;

        }
        else if (h>cx1){
            h=cx1;
            z=cx1;
        }

        \[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(startScroller) object:nil\];
        \[self performSelector:@selector(startScroller) withObject:nil afterDelay:2.0\];

    }
}
-(void) startScroller{
    if (isdragging == true) {
        isdragging=false;
    }
}

- (void) onTimer {

    if (isdragging) {
        return;
    }

    if (h > cx1) {

        if (x <= 5){
            \[headerView.scrollView setContentOffset:CGPointMake(z, 0) animated:YES\];
            x++;
            z--;
            return;
        }

        if (z <= 5){
            h=0;
        }
        z-=5;

        \[headerView.scrollView setContentOffset:CGPointMake(z, 0) animated:YES\];
    }
    else{
        x=1;
        if (z<=5) {
            \[headerView.scrollView setContentOffset:CGPointMake(h, 0) animated:YES\];
            z+=1;
        }
        else{
            h +=  5;
            z=h;
            \[headerView.scrollView setContentOffset:CGPointMake(h, 0) animated:YES\];
        }

    }
}][1]