复用机制

#import 
#import 
// 实现重用机制的类
@interface ViewReusePool : NSObject

// 从重用池当中取出一个可重用的view
- (UIView *)dequeueReusableView;

// 向重用池当中添加一个视图
- (void)addUsingView:(UIView *)view;

// 重置方法，将当前使用中的视图移动到可重用队列当中
- (void)reset;

@end


#import "ViewReusePool.h"

@interface ViewReusePool ()
// 等待使用的队列
@property (nonatomic, strong) NSMutableSet *waitUsedQueue;
// 使用中的队列
@property (nonatomic, strong) NSMutableSet *usingQueue;
@end

@implementation ViewReusePool

- (id)init{
    self = [super init];
    if (self) {
        _waitUsedQueue = [NSMutableSet set];
        _usingQueue = [NSMutableSet set];
    }
    return self;
}

- (UIView *)dequeueReusableView{
    UIView *view = [_waitUsedQueue anyObject];
    if (view == nil) {
        return nil;
    }
    else{
        // 进行队列移动
        [_waitUsedQueue removeObject:view];
        [_usingQueue addObject:view];
        return view;
    }
}

- (void)addUsingView:(UIView *)view
{
    if (view == nil) {
        return;
    }
    
    // 添加视图到使用中的队列
    [_usingQueue addObject:view];
}

- (void)reset{
    UIView *view = nil;
    while ((view = [_usingQueue anyObject])) {
        // 从使用中队列移除
        [_usingQueue removeObject:view];
        // 加入等待使用的队列
        [_waitUsedQueue addObject:view];
    }
}

@end

#import 

@protocol IndexedTableViewDataSource 

// 获取一个tableview的字母索引条数据的方法
- (NSArray  *)indexTitlesForIndexTableView:(UITableView *)tableView;

@end

@interface IndexedTableView : UITableView
@property (nonatomic, weak) id  indexedDataSource;
@end



#import "IndexedTableView.h"
#import "ViewReusePool.h"
@interface IndexedTableView ()
{
    UIView *containerView;
    ViewReusePool *reusePool;
}
@end

@implementation IndexedTableView

- (void)reloadData{
    [super reloadData];
    
    // 懒加载
    if (containerView == nil) {
        containerView = [[UIView alloc] initWithFrame:CGRectZero];
        containerView.backgroundColor = [UIColor whiteColor];
        
        //避免索引条随着table滚动
        [self.superview insertSubview:containerView aboveSubview:self];
    }
    
    if (reusePool == nil) {
        reusePool = [[ViewReusePool alloc] init];
    }
    
    // 标记所有视图为可重用状态
    [reusePool reset];
    
    // reload字母索引条
    [self reloadIndexedBar];
}

- (void)reloadIndexedBar
{
    // 获取字母索引条的显示内容
    NSArray  *arrayTitles = nil;
    if ([self.indexedDataSource respondsToSelector:@selector(indexTitlesForIndexTableView:)]) {
        arrayTitles = [self.indexedDataSource indexTitlesForIndexTableView:self];
    }
    
    // 判断字母索引条是否为空
    if (!arrayTitles || arrayTitles.count <= 0) {
        [containerView setHidden:YES];
        return;
    }
    
    NSUInteger count = arrayTitles.count;
    CGFloat buttonWidth = 60;
    CGFloat buttonHeight = self.frame.size.height / count;
    
    for (int i = 0; i < [arrayTitles count]; i++) {
        NSString *title = [arrayTitles objectAtIndex:i];
        
        // 从重用池当中取一个Button出来
        UIButton *button = (UIButton *)[reusePool dequeueReusableView];
        // 如果没有可重用的Button重新创建一个
        if (button == nil) {
            button = [[UIButton alloc] initWithFrame:CGRectZero];
            button.backgroundColor = [UIColor whiteColor];
            
            // 注册button到重用池当中
            [reusePool addUsingView:button];
            NSLog(@"新创建一个Button");
        }
        else{
            NSLog(@"Button 重用了");
        }
        
        // 添加button到父视图控件
        [containerView addSubview:button];
        [button setTitle:title forState:UIControlStateNormal];
        [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
        
        // 设置button的坐标
        [button setFrame:CGRectMake(0, i * buttonHeight, buttonWidth, buttonHeight)];
    }
    
    [containerView setHidden:NO];
    containerView.frame = CGRectMake(self.frame.origin.x + self.frame.size.width - buttonWidth, self.frame.origin.y, buttonWidth, self.frame.size.height);
}


@end

#import "ViewController.h"
#import "IndexedTableView.h"
@interface ViewController ()
{
    IndexedTableView *tableView;//带有索引条的tableview
    UIButton *button;
    NSMutableArray *dataSource;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //创建一个Tableview
    tableView = [[IndexedTableView alloc] initWithFrame:CGRectMake(0, 60, self.view.frame.size.width, self.view.frame.size.height - 60) style:UITableViewStylePlain];
    tableView.delegate = self;
    tableView.dataSource = self;
    
    // 设置table的索引数据源
    tableView.indexedDataSource = self;
    
    [self.view addSubview:tableView];
    
    //创建一个按钮
    button = [[UIButton alloc] initWithFrame:CGRectMake(0, 20, self.view.frame.size.width, 40)];
    button.backgroundColor = [UIColor redColor];
    [button setTitle:@"reloadTable" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(doAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
    
    // 数据源
    dataSource = [NSMutableArray array];
    for (int i = 0; i < 100; i++) {
        [dataSource addObject:@(i+1)];
    }
    // Do any additional setup after loading the view, typically from a nib.
    
}

#pragma mark IndexedTableViewDataSource

- (NSArray  *)indexTitlesForIndexTableView:(UITableView *)tableView{
    
    //奇数次调用返回6个字母，偶数次调用返回11个
    static BOOL change = NO;
    
    if (change) {
        change = NO;
        return @[@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",@"K"];
    }
    else{
        change = YES;
        return @[@"A",@"B",@"C",@"D",@"E",@"F"];
    }
    
}

#pragma mark UITableViewDataSource

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [dataSource count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *identifier = @"reuseId";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    //如果重用池当中没有可重用的cell，那么创建一个cell
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
    }
    // 文案设置
    cell.textLabel.text = [[dataSource objectAtIndex:indexPath.row] stringValue];
    
    //返回一个cell
    return cell;
}

#pragma mark - UITableViewDelegate

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    return 40;
}

- (void)doAction:(id)sender{
    NSLog(@"reloadData");
    [tableView reloadData];
}

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


@end