自定义UISlider无法到达边缘

Question

所以我制作了一个自定义的UISlider，但拇指不会到达轨道的终点。有没有办法来解决这个问题？

- (id)initWithCoder:(NSCoder *)aDecoder
{
    if (self = [super initWithCoder:aDecoder])
    {
        [self setThumbImage:         [UIImage imageNamed:@"Thumb.png"]  forState:UIControlStateNormal];
        [self setMinimumTrackImage:  [[UIImage imageNamed:@"Min.png"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 5, 0, 0)] forState:UIControlStateNormal];
        [self setMaximumTrackImage:  [[UIImage imageNamed:@"Max.png"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 0, 0, 5)] forState:UIControlStateNormal];
    }
    return self;
}