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 = 66+y*height/allHeight;
        if (myScrollViewIndirect.top < 66)
        {
            myScrollViewIndirect.top = 66;
        }
    }
    else
    {
        CGFloat y1 = (allHeight-height-y);
        myScrollViewIndirect.bottom = 62+height-y1*height/allHeight;
        if (myScrollViewIndirect.bottom>62+height)
        {
            myScrollViewIndirect.bottom = 62+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(0, 64, 3, 0) andBackgroundColor:[UIColor grayColor]];
    myScrollViewIndirect.layer.cornerRadius = myScrollViewIndirect.width/2.0;
    myScrollViewIndirect.right = SCREEN_WIDTH-3;
    [self.view addSubview:myScrollViewIndirect];
    
    myLabel = [LMFUITools createLabelWithFrame:CGRectMake(0, 0, 100, 0) andBackgroundColor:[UIColor cyanColor] andTextAlignment:NSTextAlignmentCenter andFont:[UIFont systemFontOfSize:17] andText:@"" andTextColor:[UIColor blackColor]];
    myLabel.right = myScrollViewIndirect.left-2;
    [self.view addSubview:myLabel];
    
    [self loadData];

}

- (void)loadData
{
    for (int i=0; i<40; 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 = 20;
    float width = height * 16 / 28;
    UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(6, 20, 60, 44)];
    [self.view addSubview:leftView];
    UIImageView *image = [LMFUITools createImageView:CGRectMake(10, (44-height)/2, 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(0, 20, SCREEN_WIDTH/2.0, 44) andBackgroundColor:nil andTextAlignment:NSTextAlignmentCenter andFont:[UIFont systemFontOfSize:17] 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(0, 0, 120, 44)];
    rightView.right = SCREEN_WIDTH;
    rightView.top = 20;
    [self.view addSubview:rightView];
    
    UIImageView *rightImage = [LMFUITools createImageView:CGRectMake(0, 0, 44, 44) andBackgroundImage:@""];
    [rightView addSubview:rightImage];
    UILabel *label = [LMFUITools createLabelWithFrame:CGRectMake(0, 0, 44, 44) andBackgroundColor:nil andTextAlignment:NSTextAlignmentLeft andFont:[UIFont systemFontOfSize:15] 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(0, 64, SCREEN_WIDTH, SCREEN_HEIGHT-64) 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(0, 0)];
}

#pragma mark --tableview delegate
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    return 44;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.dataArray count];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}
- (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 = 0;
    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 = 40;
    CGFloat height = count*44.0;
    if (y>height-self.tableView.height)
    {
        subCount = -SUBCOUNT;
    }
    else if (y<0)
    {
        subCount = SUBCOUNT;
    }
    [self.tableView setContentOffset:CGPointMake(0, 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<0)
    {
        currentHeight += y;
    }
    if (y+height>allHeight)
    {
        CGFloat h = fabs(y+height-allHeight);
        currentHeight -= h;
    }
    
    if (currentHeight<8)
    {
        myScrollViewIndirect.height = 8;
    }
    else
    {
        myScrollViewIndirect.height = currentHeight;
    }
    
    if (y+height/2.0<=allHeight/2.0)
    {
        myScrollViewIndirect.top = 66+y*height/allHeight;
        if (myScrollViewIndirect.top < 66)
        {
            myScrollViewIndirect.top = 66;
        }
    }
    else
    {
        CGFloat y1 = (allHeight-height-y);
        myScrollViewIndirect.bottom = 62+height-y1*height/allHeight;
        if (myScrollViewIndirect.bottom>62+height)
        {
            myScrollViewIndirect.bottom = 62+height;
        }
    }
    myLabel.height = 20;
    myLabel.centerY = myScrollViewIndirect.centerY;
    if (myLabel.top < 66)
    {
        myLabel.top = 66;
    }
    if (myLabel.bottom>62+height)
    {
        myLabel.bottom = 62+height;
    }
    CGFloat centerY = myLabel.centerY+y-64;
    for (NSInteger i=0; i<[self.dataArray count]; i++)
    {
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];
        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