效果：

image.png

源代码

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface SliderView : UIView
//刷新
-(void)SliderViewRefreshingDidScroll:(UIScrollView *)scrollView;
-(instancetype)initWithFrame:(CGRect)frame ScrollView:(UIScrollView *)scrollView;

@end

#import "SliderView.h"
@interface SliderView()<UIGestureRecognizerDelegate>
@property (strong, nonatomic)UIPanGestureRecognizer *panGestureRecognizer  ;
@property (strong, nonatomic) UIScrollView * scrollView;
@end
@implementation SliderView
-(SliderView *)initWithFrame:(CGRect)frame ScrollView:(UIScrollView *)scrollView
{
    if (self = [super initWithFrame:frame]) {
        self.scrollView = scrollView;
        CGFloat safeAreaTop = 0;
        if (@available(iOS 11.0, *)) {
            safeAreaTop = self.scrollView.safeAreaInsets.top;
            self.scrollView.showsVerticalScrollIndicator = NO;
            self.frame = CGRectMake(self.frame.origin.x, self.frame.origin.y+safeAreaTop, self.width, self.height);
            
        }
        [self creatSubViews];
    }
    return self;
}
-(instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        [self creatSubViews];
    }
    return self;
}
-(void)creatSubViews
{
    self.backgroundColor = [UIColor clearColor];
    UIImageView * imageView = [[UIImageView alloc] init];
    imageView.image = [UIImage imageNamed:@"huakuai"];
    [self addSubview:imageView];
    imageView.userInteractionEnabled = NO;
    [imageView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerY.mas_offset(0);
        make.centerX.mas_offset(0);
        
    }];
    self.panGestureRecognizer = [[UIPanGestureRecognizer alloc]
                                 initWithTarget:self
                                 action:@selector(handlePan:)];
    self.panGestureRecognizer.delegate = self;
    [self addGestureRecognizer: self.panGestureRecognizer];
}
- (void) handlePan:(UIPanGestureRecognizer*) recognizer
{
    // 手指滑动坐标
    CGPoint translation = [recognizer translationInView:self.superview];
    //Y轴位置
    CGFloat Y = recognizer.view.center.y + translation.y;
    CGFloat height = self.scrollView.height-self.frame.size.height;
    CGFloat safeAreaBottom = 0 ;
    CGFloat safeAreaTop = 0 ;
    //ios 11 适配安全距离，安全距离区域不能滑动
    if (@available(iOS 11.0, *)) {
        safeAreaBottom = self.scrollView.safeAreaInsets.bottom;
        safeAreaTop =  self.scrollView.safeAreaInsets.top;
        height = height - safeAreaBottom-safeAreaTop;
        
    }
    // 超出最小范围
    // 中心Y+self.frame.size.height/2+safeAreaTop = Y
    if ((Y-self.frame.size.height/2-safeAreaTop)<0) {
        //safeAreaTop+self.frame.size.height/2 起始位置
        recognizer.view.centerY = safeAreaTop+self.frame.size.height/2;
        [recognizer setTranslation:CGPointZero inView:self.superview];
        [self SliderViewPanDidScroll];
        
    }else if(Y-self.frame.size.height/2-safeAreaTop<height) {//可以滑动区域
        recognizer.view.centerY = Y;
        [recognizer setTranslation:CGPointZero inView:self.superview];
        [self SliderViewPanDidScroll];
    }
    else{//超出最大范围
        // height+self.frame.size.height/2+safeAreaTop 终点位置
        recognizer.view.centerY = height+self.frame.size.height/2+safeAreaTop;
        [recognizer setTranslation:CGPointZero inView:self.superview];
        [self SliderViewPanDidScroll];
    }
    
}
-(void)SliderViewPanDidScroll
{
    if (!self.scrollView) {
        return;
    }
    //scrollView 内容高度-安全距离 = 可以偏移的高度
    CGFloat allHeight = self.scrollView.contentSize.height;
    //滑动的高度
    CGFloat sliderH = self.frame.size.height;
    // 滑块可以滑动的高度
    CGFloat height = self.scrollView.height-sliderH;
    //
    CGFloat safeAreaBottom = 0 ;
    CGFloat safeAreaTop = 0;
    if (@available(iOS 11.0, *)) {
        safeAreaBottom = self.scrollView.safeAreaInsets.bottom;
        safeAreaTop = self.scrollView.safeAreaInsets.top;
        height = height - safeAreaBottom - safeAreaTop;
        allHeight = allHeight - safeAreaBottom ;
    }
    CGFloat MaxOffSetY = self.scrollView.contentSize.height-self.scrollView.height+safeAreaBottom;
    CGFloat offsetY   = (self.frame.origin.y-safeAreaTop-sliderH/2)/height*allHeight+safeAreaTop;
    CGFloat minOffSet = -safeAreaTop;
    if (offsetY>MaxOffSetY) {
        offsetY = MaxOffSetY;
    }
    if (offsetY<minOffSet) {
        offsetY = minOffSet;
    }
    [self.scrollView setContentOffset:CGPointMake(0, offsetY)];
    
}

-(void)SliderViewRefreshingDidScroll:(UIScrollView *)scrollView
{
    if ( self.panGestureRecognizer.state!=UIGestureRecognizerStatePossible ) {
        return;
    }
    CGFloat offsetY = scrollView.contentOffset.y;
    CGFloat safeAreaBottom = 0 ;
    CGFloat safeAreaTop = 0 ;
    CGFloat sliderH = self.frame.size.height;
    CGFloat allHeight = scrollView.contentSize.height;
    CGFloat height = scrollView.height-sliderH;
    if (@available(iOS 11.0, *)) {
        safeAreaBottom = scrollView.safeAreaInsets.bottom;
        safeAreaTop = scrollView.safeAreaInsets.top;
        
        height = height - safeAreaBottom-safeAreaTop;
    }
    CGFloat Y = offsetY/allHeight * height+safeAreaTop;
    if (offsetY <= 0) {
        self.frame =  CGRectMake(self.frame.origin.x, Y, self.width, sliderH);
    }else{
        if (Y<height) {
            self.frame =  CGRectMake(self.frame.origin.x, Y, self.width, sliderH);
        }else{
            self.frame =  CGRectMake(self.frame.origin.x,height+safeAreaTop, self.width, sliderH);
        }
    }
    
}
@end

使用

-(SliderView *)sliderView
{
    if (!_sliderView) {
        _sliderView = [[SliderView alloc] initWithFrame:CGRectMake(ScreenWidth/3.0*2-15, 0, 15, 30) ScrollView:self.tableView];
    }
    return  _sliderView;
}
@end

-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    [self.sliderView SliderViewRefreshingDidScroll:scrollView];
}