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。

  1 #define SUBCOUNT 0.2
  2 #import "ALDayPictureWallViewController.h"
  3 #import "ALGoalPictureWallViewController.h"
  4 
  5 @interface ALDayPictureWallViewController ()<UITableViewDelegate,UITableViewDataSource>
  6 {
  7     NSTimer *timer;
  8     CGFloat subCount;
  9     CGFloat y;
 10     //自定义滑动块
 11     UIView *myScrollViewIndirect;
 12     UILabel *myLabel;
 13     NSInteger cellCount;
 14 }
 15 @property (nonatomic, strong) UITableView *tableView;
 16 @property (nonatomic, strong) NSMutableArray *dataArray;
 17 
 18 @end
 19 
 20 @implementation ALDayPictureWallViewController
 21 
 22 - (void)viewDidLoad {
 23     [super viewDidLoad];
 24     // Do any additional setup after loading the view.
 25     self.view.backgroundColor = [UIColor whiteColor];
 26     subCount = SUBCOUNT;
 27     [self createNavi];
 28     [self createUI];
 29     
 30     myScrollViewIndirect = [LMFUITools createView:CGRectMake(0, 64, 3, 0) andBackgroundColor:[UIColor grayColor]];
 31     myScrollViewIndirect.layer.cornerRadius = myScrollViewIndirect.width/2.0;
 32     myScrollViewIndirect.right = SCREEN_WIDTH-3;
 33     [self.view addSubview:myScrollViewIndirect];
 34     
 35     myLabel = [LMFUITools createLabelWithFrame:CGRectMake(0, 0, 100, 0) andBackgroundColor:[UIColor cyanColor] andTextAlignment:NSTextAlignmentCenter andFont:[UIFont systemFontOfSize:17] andText:@"" andTextColor:[UIColor blackColor]];
 36     myLabel.right = myScrollViewIndirect.left-2;
 37     [self.view addSubview:myLabel];
 38     
 39     [self loadData];
 40 
 41 }
 42 
 43 - (void)loadData
 44 {
 45     for (int i=0; i<40; i++)
 46     {
 47         NSString *str = [NSString stringWithFormat:@"第%i行", i];
 48         [self.dataArray addObject:str];
 49     }
 50     [self.tableView reloadData];
 51 }
 52 
 53 - (NSMutableArray *)dataArray
 54 {
 55     if (_dataArray == nil)
 56     {
 57         _dataArray = [NSMutableArray array];
 58     }
 59     return _dataArray;
 60 }
 61 
 62 - (void)createNavi
 63 {
 64     float height = 20;
 65     float width = height * 16 / 28;
 66     UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(6, 20, 60, 44)];
 67     [self.view addSubview:leftView];
 68     UIImageView *image = [LMFUITools createImageView:CGRectMake(10, (44-height)/2, width, height) andBackgroundImage:@"naviBlack_image"];
 69     [leftView addSubview:image];
 70     UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(goBackView:)];
 71     [leftView addGestureRecognizer:tap];
 72     
 73     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]];
 74     titleLable.centerX = SCREEN_WIDTH * 0.5;
 75     [self.view addSubview:titleLable];
 76     
 77     //平铺
 78     UIView *rightView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 120, 44)];
 79     rightView.right = SCREEN_WIDTH;
 80     rightView.top = 20;
 81     [self.view addSubview:rightView];
 82     
 83     UIImageView *rightImage = [LMFUITools createImageView:CGRectMake(0, 0, 44, 44) andBackgroundImage:@""];
 84     [rightView addSubview:rightImage];
 85     UILabel *label = [LMFUITools createLabelWithFrame:CGRectMake(0, 0, 44, 44) andBackgroundColor:nil andTextAlignment:NSTextAlignmentLeft andFont:[UIFont systemFontOfSize:15] andText:@"平铺" andTextColor:[UIColor colorWithHexString:@"#999999"]];
 86     label.left = rightImage.right;
 87     [rightView addSubview:label];
 88     
 89     UITapGestureRecognizer *goalPictureTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(startTimer)];
 90     [rightView addGestureRecognizer:goalPictureTap];
 91 }
 92 
 93 - (void)startTimer
 94 {
 95     if (timer == nil)
 96     {
 97         timer = [NSTimer scheduledTimerWithTimeInterval:0.002 target:self selector:@selector(startScrollTableView) userInfo:nil repeats:YES];
 98         self.tableView.userInteractionEnabled = NO;
 99         [timer fire];
100     }
101     else
102     {
103         [timer setFireDate:[NSDate distantFuture]];
104         timer = nil;
105         [timer invalidate];
106         self.tableView.userInteractionEnabled = YES;
107     }
108 }
109 
110 - (void)createUI
111 {
112     self.tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 64, SCREEN_WIDTH, SCREEN_HEIGHT-64) style:UITableViewStylePlain];
113     self.tableView.backgroundColor = [UIColor colorWithHexString:@"#f5f5f5"];
114 //    self.tableView.showsVerticalScrollIndicator = NO;
115 //    self.tableView.showsHorizontalScrollIndicator = NO;
116 //    self.tableView.separatorInset = UIEdgeInsetsZero;
117 //    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
118     self.tableView.delegate = self;
119     self.tableView.dataSource = self;
120     [self.view addSubview:self.tableView];
121     [self.tableView setContentOffset:CGPointMake(0, 0)];
122 }
123 
124 #pragma mark --tableview delegate
125 - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
126 {
127     return 44;
128 }
129 
130 - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
131 {
132     return [self.dataArray count];
133 }
134 - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
135 {
136     return 1;
137 }
138 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
139 {
140     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"UITableViewCell"];
141     if (cell == nil)
142     {
143         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"UITableViewCell"];
144     }
145     if ([self.dataArray count])
146     {
147         cell.textLabel.text = [self.dataArray objectAtIndex:indexPath.row];
148     }
149     
150     cell.selectionStyle = 0;
151     return cell;
152 }
153 
154 - (void)goalPicture:(UITapGestureRecognizer *)gesture
155 {
156     ALGoalPictureWallViewController *goalPictureView = [[ALGoalPictureWallViewController alloc] init];
157     self.hidesBottomBarWhenPushed = YES;
158     [self.navigationController pushViewController:goalPictureView animated:YES];
159 }
160 
161 #pragma mark --开始滑动
162 - (void)startScrollTableView
163 {
164     y+=subCount;
165     NSInteger count = 40;
166     CGFloat height = count*44.0;
167     if (y>height-self.tableView.height)
168     {
169         subCount = -SUBCOUNT;
170     }
171     else if (y<0)
172     {
173         subCount = SUBCOUNT;
174     }
175     [self.tableView setContentOffset:CGPointMake(0, y)];
176 }
177 
178 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
179 {
180     NSLog(@"contentOffset.y      %f", scrollView.contentOffset.y);
181     y = scrollView.contentOffset.y;
182     
183     //需要tableview的contentoffset.y，tableview的高度，tableview画布的高度
184     CGFloat height = scrollView.height;
185     CGFloat allHeight = scrollView.contentSize.height;
186     
187     //计算自定义滑块的高度
188     myScrollViewIndirect.height = height*height/allHeight;
189     //控件的高度不能设为负数，它会自动转化为正数，阿西吧
190     float currentHeight = myScrollViewIndirect.height;
191     //计算滑块
192     //如果tableview的中心在画框的上部，通过top确定滑块的位置
193     
194     if (y<0)
195     {
196         currentHeight += y;
197     }
198     if (y+height>allHeight)
199     {
200         CGFloat h = fabs(y+height-allHeight);
201         currentHeight -= h;
202     }
203     
204     if (currentHeight<8)
205     {
206         myScrollViewIndirect.height = 8;
207     }
208     else
209     {
210         myScrollViewIndirect.height = currentHeight;
211     }
212     
213     if (y+height/2.0<=allHeight/2.0)
214     {
215         myScrollViewIndirect.top = 66+y*height/allHeight;
216         if (myScrollViewIndirect.top < 66)
217         {
218             myScrollViewIndirect.top = 66;
219         }
220     }
221     else
222     {
223         CGFloat y1 = (allHeight-height-y);
224         myScrollViewIndirect.bottom = 62+height-y1*height/allHeight;
225         if (myScrollViewIndirect.bottom>62+height)
226         {
227             myScrollViewIndirect.bottom = 62+height;
228         }
229     }
230     myLabel.height = 20;
231     myLabel.centerY = myScrollViewIndirect.centerY;
232     if (myLabel.top < 66)
233     {
234         myLabel.top = 66;
235     }
236     if (myLabel.bottom>62+height)
237     {
238         myLabel.bottom = 62+height;
239     }
240     CGFloat centerY = myLabel.centerY+y-64;
241     for (NSInteger i=0; i<[self.dataArray count]; i++)
242     {
243         NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];
244         CGRect rectInTableView = [self.tableView rectForRowAtIndexPath:indexPath];
245 //        CGRect rect = [self.tableView convertRect:rectInTableView toView:[self.tableView superview]];
246         if (rectInTableView.origin.y<=centerY && centerY<=rectInTableView.origin.y+rectInTableView.size.height)
247         {
248             NSLog(@"cell.y=%f  cellHeight=%f", rectInTableView.origin.y, rectInTableView.size.height);
249             myLabel.text = [self.dataArray objectAtIndex:i];
250             return;
251         }
252         if (rectInTableView.origin.y > centerY)
253         {
254             NSLog(@"cell.y=%f  cellHeight=%f", rectInTableView.origin.y, rectInTableView.size.height);
255             return;
256         }
257     }
258 }
259 
260 - (void)goBackView:(UITapGestureRecognizer *)gesture
261 {
262     [self.navigationController popViewControllerAnimated:YES];
263 }
264 
265 - (void)viewWillAppear:(BOOL)animated
266 {
267     [super viewWillAppear:animated];
268     self.navigationController.navigationBar.hidden = YES;
269 }
270 
271 - (void)viewWillDisappear:(BOOL)animated
272 {
273     [super viewWillDisappear:animated];
274     [timer setFireDate:[NSDate distantFuture]];
275     timer = nil;
276     [timer invalidate];
277     self.navigationController.navigationBar.hidden = NO;
278 }
279 
280 - (void)didReceiveMemoryWarning {
281     [super didReceiveMemoryWarning];
282     // Dispose of any resources that can be recreated.
283 }
284 
285 @end