自定义scrollview右侧的滑动条

　　在做这个功能之前我其实是拒绝的，为什么这么说呢，因为我怕麻烦啊！（开玩笑的，怕麻烦就不做程序员了）

　　很久没有写博客，这次刚好项目中有个有趣的东西，想拿出来分享一下，希望能帮到某些小伙伴。

　　首先说说需求，是这样的：

　　在tableview滑动的过程中，右侧的滑动条中间放一个label随着滑动条一起滑动，并且它的centerY与滑动条的centerY相等。当然，在滑到顶部或者尾部的时候label不能超出tableview的范围。

然后label上面显示与之对应的cell的内容。

　　刚开始想用系统提供的滑动条，scrollIndicator，没啥用啊。就提供了一个方法，没办法完成这种效果，只能自定义一个。下面有几个变量，我先设置一下，height：tableview的高度，allHeight:tableview内容的高度，y：tableview的contentoffset.y，currentHeight：滑动条的高度。

　　1.猜想，currentHeight／height＝height／allHeight，然后去证实这一猜想，结果是有几个像素的偏差，不过并不影响。

　　2.确定滑动块的位置，要判断画框在画布的上半部分还是下半部分，在上面用top，在下面用bottom（没看明白继续往下看，有完整的代码）：

if (y+height/2.0<=allHeight/2.0)
    {
        myScrollViewIndirect.top = +y*height/allHeight;
        if (myScrollViewIndirect.top < )
        {
            myScrollViewIndirect.top = ;
        }
    }
    else
    {
        CGFloat y1 = (allHeight-height-y);
        myScrollViewIndirect.bottom = +height-y1*height/allHeight;
        if (myScrollViewIndirect.bottom>+height)
        {
            myScrollViewIndirect.bottom = +height;
        }
    }

　　3.滑块的位置的高度确定了，相当于已经完成了一半，接下来是确定label的位置，这就简单了，将滑动条的centerY给label的centerY就可以了。不过滑到最顶部，而且继续往下拉，滑动到最底部继续往上拉的时候需要判断一下label的位置。很简单的条件语句，后面有。

　　4.最核心的功能，label显示其所在位置的cell内容。通过遍历tableview里面cell的位置来判断对应的是哪一个cell，获取其下标，然后在数据源中得到内容。不过由于是遍历，我实在没脸单独把这个算法拿出来，想想以后还是学学高级一点的算法吧。

　　最后附上代码，不然就要被喷了。

 #define SUBCOUNT 0.2
 #import "ALDayPictureWallViewController.h"
 #import "ALGoalPictureWallViewController.h"

 @interface ALDayPictureWallViewController ()<UITableViewDelegate,UITableViewDataSource>
 {
     NSTimer *timer;
     CGFloat subCount;
     CGFloat y;
     //自定义滑动块
     UIView *myScrollViewIndirect;
     UILabel *myLabel;
     NSInteger cellCount;
 }
 @property (nonatomic, strong) UITableView *tableView;
 @property (nonatomic, strong) NSMutableArray *dataArray;

 @end

 @implementation ALDayPictureWallViewController

 - (void)viewDidLoad {
     [super viewDidLoad];
     // Do any additional setup after loading the view.
     self.view.backgroundColor = [UIColor whiteColor];
     subCount = SUBCOUNT;
     [self createNavi];
     [self createUI];

     myScrollViewIndirect = [LMFUITools createView:CGRectMake(, , , ) andBackgroundColor:[UIColor grayColor]];
     myScrollViewIndirect.layer.cornerRadius = myScrollViewIndirect.width/2.0;
     myScrollViewIndirect.right = SCREEN_WIDTH-;
     [self.view addSubview:myScrollViewIndirect];

     myLabel = [LMFUITools createLabelWithFrame:CGRectMake(, , , ) andBackgroundColor:[UIColor cyanColor] andTextAlignment:NSTextAlignmentCenter andFont:[UIFont systemFontOfSize:] andText:@"" andTextColor:[UIColor blackColor]];
     myLabel.right = myScrollViewIndirect.left-;
     [self.view addSubview:myLabel];

     [self loadData];

 }

 - (void)loadData
 {
     for (int i=; i<; i++)
     {
         NSString *str = [NSString stringWithFormat:@"第%i行", i];
         [self.dataArray addObject:str];
     }
     [self.tableView reloadData];
 }

 - (NSMutableArray *)dataArray
 {
     if (_dataArray == nil)
     {
         _dataArray = [NSMutableArray array];
     }
     return _dataArray;
 }

 - (void)createNavi
 {
     float height = ;
     float width = height *  / ;
     UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(, , , )];
     [self.view addSubview:leftView];
     UIImageView *image = [LMFUITools createImageView:CGRectMake(, (-height)/, width, height) andBackgroundImage:@"naviBlack_image"];
     [leftView addSubview:image];
     UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(goBackView:)];
     [leftView addGestureRecognizer:tap];

     UILabel *titleLable = [LMFUITools createLabelWithFrame:CGRectMake(, , SCREEN_WIDTH/2.0, ) andBackgroundColor:nil andTextAlignment:NSTextAlignmentCenter andFont:[UIFont systemFontOfSize:] andText:@"照片墙" andTextColor:[UIColor blackColor]];
     titleLable.centerX = SCREEN_WIDTH * 0.5;
     [self.view addSubview:titleLable];

     //平铺
     UIView *rightView = [[UIView alloc] initWithFrame:CGRectMake(, , , )];
     rightView.right = SCREEN_WIDTH;
     rightView.top = ;
     [self.view addSubview:rightView];

     UIImageView *rightImage = [LMFUITools createImageView:CGRectMake(, , , ) andBackgroundImage:@""];
     [rightView addSubview:rightImage];
     UILabel *label = [LMFUITools createLabelWithFrame:CGRectMake(, , , ) andBackgroundColor:nil andTextAlignment:NSTextAlignmentLeft andFont:[UIFont systemFontOfSize:] andText:@"平铺" andTextColor:[UIColor colorWithHexString:@"#999999"]];
     label.left = rightImage.right;
     [rightView addSubview:label];

     UITapGestureRecognizer *goalPictureTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(startTimer)];
     [rightView addGestureRecognizer:goalPictureTap];
 }

 - (void)startTimer
 {
     if (timer == nil)
     {
         timer = [NSTimer scheduledTimerWithTimeInterval:0.002 target:self selector:@selector(startScrollTableView) userInfo:nil repeats:YES];
         self.tableView.userInteractionEnabled = NO;
         [timer fire];
     }
     else
     {
         [timer setFireDate:[NSDate distantFuture]];
         timer = nil;
         [timer invalidate];
         self.tableView.userInteractionEnabled = YES;
     }
 }

 - (void)createUI
 {
     self.tableView = [[UITableView alloc] initWithFrame:CGRectMake(, , SCREEN_WIDTH, SCREEN_HEIGHT-) style:UITableViewStylePlain];
     self.tableView.backgroundColor = [UIColor colorWithHexString:@"#f5f5f5"];
 //    self.tableView.showsVerticalScrollIndicator = NO;
 //    self.tableView.showsHorizontalScrollIndicator = NO;
 //    self.tableView.separatorInset = UIEdgeInsetsZero;
 //    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
     self.tableView.delegate = self;
     self.tableView.dataSource = self;
     [self.view addSubview:self.tableView];
     [self.tableView setContentOffset:CGPointMake(, )];
 }

 #pragma mark --tableview delegate
 - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
 {
     return ;
 }

 - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
 {
     return [self.dataArray count];
 }
 - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
 {
     return ;
 }
 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
 {
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"UITableViewCell"];
     if (cell == nil)
     {
         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"UITableViewCell"];
     }
     if ([self.dataArray count])
     {
         cell.textLabel.text = [self.dataArray objectAtIndex:indexPath.row];
     }

     cell.selectionStyle = ;
     return cell;
 }

 - (void)goalPicture:(UITapGestureRecognizer *)gesture
 {
     ALGoalPictureWallViewController *goalPictureView = [[ALGoalPictureWallViewController alloc] init];
     self.hidesBottomBarWhenPushed = YES;
     [self.navigationController pushViewController:goalPictureView animated:YES];
 }

 #pragma mark --开始滑动
 - (void)startScrollTableView
 {
     y+=subCount;
     NSInteger count = ;
     CGFloat height = count*44.0;
     if (y>height-self.tableView.height)
     {
         subCount = -SUBCOUNT;
     }
     else if (y<)
     {
         subCount = SUBCOUNT;
     }
     [self.tableView setContentOffset:CGPointMake(, y)];
 }

 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
 {
     NSLog(@"contentOffset.y      %f", scrollView.contentOffset.y);
     y = scrollView.contentOffset.y;

     //需要tableview的contentoffset.y，tableview的高度，tableview画布的高度
     CGFloat height = scrollView.height;
     CGFloat allHeight = scrollView.contentSize.height;

     //计算自定义滑块的高度
     myScrollViewIndirect.height = height*height/allHeight;
     //控件的高度不能设为负数，它会自动转化为正数，阿西吧
     float currentHeight = myScrollViewIndirect.height;
     //计算滑块
     //如果tableview的中心在画框的上部，通过top确定滑块的位置

     if (y<)
     {
         currentHeight += y;
     }
     if (y+height>allHeight)
     {
         CGFloat h = fabs(y+height-allHeight);
         currentHeight -= h;
     }

     if (currentHeight<)
     {
         myScrollViewIndirect.height = ;
     }
     else
     {
         myScrollViewIndirect.height = currentHeight;
     }

     if (y+height/2.0<=allHeight/2.0)
     {
         myScrollViewIndirect.top = +y*height/allHeight;
         if (myScrollViewIndirect.top < )
         {
             myScrollViewIndirect.top = ;
         }
     }
     else
     {
         CGFloat y1 = (allHeight-height-y);
         myScrollViewIndirect.bottom = +height-y1*height/allHeight;
         if (myScrollViewIndirect.bottom>+height)
         {
             myScrollViewIndirect.bottom = +height;
         }
     }
     myLabel.height = ;
     myLabel.centerY = myScrollViewIndirect.centerY;
     if (myLabel.top < )
     {
         myLabel.top = ;
     }
     if (myLabel.bottom>+height)
     {
         myLabel.bottom = +height;
     }
     CGFloat centerY = myLabel.centerY+y-;
     for (NSInteger i=; i<[self.dataArray count]; i++)
     {
         NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:];
         CGRect rectInTableView = [self.tableView rectForRowAtIndexPath:indexPath];
 //        CGRect rect = [self.tableView convertRect:rectInTableView toView:[self.tableView superview]];
         if (rectInTableView.origin.y<=centerY && centerY<=rectInTableView.origin.y+rectInTableView.size.height)
         {
             NSLog(@"cell.y=%f  cellHeight=%f", rectInTableView.origin.y, rectInTableView.size.height);
             myLabel.text = [self.dataArray objectAtIndex:i];
             return;
         }
         if (rectInTableView.origin.y > centerY)
         {
             NSLog(@"cell.y=%f  cellHeight=%f", rectInTableView.origin.y, rectInTableView.size.height);
             return;
         }
     }
 }

 - (void)goBackView:(UITapGestureRecognizer *)gesture
 {
     [self.navigationController popViewControllerAnimated:YES];
 }

 - (void)viewWillAppear:(BOOL)animated
 {
     [super viewWillAppear:animated];
     self.navigationController.navigationBar.hidden = YES;
 }

 - (void)viewWillDisappear:(BOOL)animated
 {
     [super viewWillDisappear:animated];
     [timer setFireDate:[NSDate distantFuture]];
     timer = nil;
     [timer invalidate];
     self.navigationController.navigationBar.hidden = NO;
 }

 - (void)didReceiveMemoryWarning {
     [super didReceiveMemoryWarning];
     // Dispose of any resources that can be recreated.
 }

 @end