Slider 1 动态插入自定义view 2 调整thumb大

@interface CusSlider : UISlider

@end

@implementation CusSlider

- (CGRect)thumbRectForBounds:(CGRect)bounds trackRect:(CGRect)rect value:(float)value{

    CGFloat dif = 4;

    CGFloat difX = dif;
    rect.origin.x = rect.origin.x - difX;
    rect.size.width = rect.size.width + difX * 2;

    CGFloat difY = -0;
    rect.origin.y = rect.origin.y - difY;
    rect.size.height = rect.size.height + difY * 2;
    CGRect newRect = [super thumbRectForBounds:bounds trackRect:rect value:value];
    /* Inset `rect' by `(dx, dy)' -- i.e., offset its origin by `(dx, dy)', and
       decrease its size by `(2*dx, 2*dy)'. */
    return CGRectInset(newRect, difX, difY);
}

@end

- (void)createUI{
    // 1 自定义Slider, 重写 thumbRectForBounds 调整rect
    CusSlider * slider = [CusSlider new];
    
    // 2 新加图层
    UIView * viewRed = [UIView new];
    viewRed.layer.masksToBounds = YES;
    viewRed.backgroundColor = [UIColor redColor];
    
    // 3 延迟调整图层
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        if (slider.subviews.count > 0) {
            UIView * viewParent =  [self getSliderSubParentView:slider];
            [viewParent addSubview:viewRed];
            for (UIView * v in viewParent.subviews) {
                if ([v isKindOfClass:[UIImageView class]]) {
                    if (v.subviews.count > 0) {
                        // 系统默认图 可以通过缩放更改大小
                        CGFloat scale = 0.85;
                        UIImageView * thumbImgV = v.subviews.firstObject;
                        [thumbImgV setTransform:CGAffineTransformMakeScale(scale, scale)];
                    }else{
                        // 自定义图片
                    }
                    [viewParent insertSubview:viewRed belowSubview:v];
                }
            }
        }
    });
}

- (UIView *)getSliderSubParentView:(UISlider *)slider{
    if (slider.subviews.count == 1) { 
        return slider.subviews[0];
    }else{
        return slider;
    }
}