自定義scrollview右側的滑動條

　　在做這個功能之前我其實是拒絕的，為什么這么說呢，因為我怕麻煩啊！（開玩笑的，怕麻煩就不做程序員了）

　　很久沒有寫博客，這次剛好項目中有個有趣的東西，想拿出來分享一下，希望能幫到某些小伙伴。

　　首先說說需求，是這樣的：

　　在tableview滑動的過程中，右側的滑動條中間放一個label隨着滑動條一起滑動，並且它的centerY與滑動條的centerY相等。當然，在滑到頂部或者尾部的時候label不能超出tableview的范圍。

然后label上面顯示與之對應的cell的內容。

　　剛開始想用系統提供的滑動條，scrollIndicator，沒啥用啊。就提供了一個方法，沒辦法完成這種效果，只能自定義一個。下面有幾個變量，我先設置一下，height：tableview的高度，allHeight:tableview內容的高度，y：tableview的contentoffset.y，currentHeight：滑動條的高度。

　　1.猜想，currentHeight／height＝height／allHeight，然后去證實這一猜想，結果是有幾個像素的偏差，不過並不影響。

　　2.確定滑動塊的位置，要判斷畫框在畫布的上半部分還是下半部分，在上面用top，在下面用bottom（沒看明白繼續往下看，有完整的代碼）：

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.滑塊的位置的高度確定了，相當於已經完成了一半，接下來是確定label的位置，這就簡單了，將滑動條的centerY給label的centerY就可以了。不過滑到最頂部，而且繼續往下拉，滑動到最底部繼續往上拉的時候需要判斷一下label的位置。很簡單的條件語句，后面有。

　　4.最核心的功能，label顯示其所在位置的cell內容。通過遍歷tableview里面cell的位置來判斷對應的是哪一個cell，獲取其下標，然后在數據源中得到內容。不過由於是遍歷，我實在沒臉單獨把這個算法拿出來，想想以后還是學學高級一點的算法吧。

　　最后附上代碼，不然就要被噴了。

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

@interface ALDayPictureWallViewController ()<UITableViewDelegate,UITableViewDataSource>
{
    NSTimer *timer;
    CGFloat subCount;
    CGFloat y;
    //自定義滑動塊
    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:@"照片牆" andTextColor:[UIColor blackColor]];
    titleLable.centerX = SCREEN_WIDTH * 0.5;
    [self.view addSubview:titleLable];
    
    //平鋪
    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:@"平鋪" 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 --開始滑動
- (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畫布的高度
    CGFloat height = scrollView.height;
    CGFloat allHeight = scrollView.contentSize.height;
    
    //計算自定義滑塊的高度
    myScrollViewIndirect.height = height*height/allHeight;
    //控件的高度不能設為負數，它會自動轉化為正數，阿西吧
    float currentHeight = myScrollViewIndirect.height;
    //計算滑塊
    //如果tableview的中心在畫框的上部，通過top確定滑塊的位置
    
    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