133自动滚动到被选中单元格（扩展知识：滚动到头部和底部）

效果如下：

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UITableViewController
@property (strong, nonatomic) NSMutableArray *mArrDataSource;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()
- (void)layoutUI;
- (UIBarButtonItem *)barButtonItemForToolbar:(NSString *)title selectorName:(NSString *)selectorName;
- (void)scrollToTopDidPush:(UIBarButtonItem *)sender;
- (void)scrollToSelectedRowDidPush:(UIBarButtonItem *)sender;
- (void)scrollToBottomDidPush:(UIBarButtonItem *)sender;
@end

@implementation ViewController
#define kRowCount 64

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self layoutUI];
}

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

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    [self.navigationController setNavigationBarHidden:NO animated:animated];
    [self.navigationController setToolbarHidden:NO animated:animated];
}

- (void)layoutUI {
    _mArrDataSource = [[NSMutableArray alloc] initWithCapacity:kRowCount];
    for (NSUInteger i=0; i<kRowCount; i++) {
        [_mArrDataSource addObject:[NSNumber numberWithUnsignedInteger:i]];
    }
    [self.tableView setAllowsSelection:YES]; //设置在普通状态中，是否允许选中；默认值为YES
    [self.tableView setAllowsSelectionDuringEditing:YES]; //设置在编辑状态中，是否允许选中；默认值为YES
    
    self.navigationItem.title = @"自动滚动到被选中单元格";
    UIBarButtonItem *barBtnScrollToTop = [self barButtonItemForToolbar:@"滚动到头部" selectorName:@"scrollToTopDidPush:"];
    UIBarButtonItem *barBtnScrollToSelectedRow = [self barButtonItemForToolbar:@"滚动到被选中单元格" selectorName:@"scrollToSelectedRowDidPush:"];
    UIBarButtonItem *barBtnScrollToBottom = [self barButtonItemForToolbar:@"滚动到底部" selectorName:@"scrollToBottomDidPush:"];
    self.toolbarItems = @[barBtnScrollToTop, barBtnScrollToSelectedRow, barBtnScrollToBottom];
}

- (UIBarButtonItem *)barButtonItemForToolbar:(NSString *)title selectorName:(NSString *)selectorName {
    UIBarButtonItem *barBtnItem = [[UIBarButtonItem alloc] initWithTitle:title
                                                                   style:UIBarButtonItemStyleDone
                                                                  target:self
                                                                  action:NSSelectorFromString(selectorName)];
    return barBtnItem;
}

- (void)scrollToTopDidPush:(UIBarButtonItem *)sender {
    [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]
                          atScrollPosition:UITableViewScrollPositionTop
                                                      animated:YES];
}

- (void)scrollToSelectedRowDidPush:(UIBarButtonItem *)sender {
    [self.tableView scrollToNearestSelectedRowAtScrollPosition:UITableViewScrollPositionNone
                                                      animated:YES];
    
    /*
     typedef NS_ENUM(NSInteger, UITableViewScrollPosition) {
     UITableViewScrollPositionNone,
     UITableViewScrollPositionTop,
     UITableViewScrollPositionMiddle,
     UITableViewScrollPositionBottom
     };                // scroll so row of interest is completely visible at top/center/bottom of view
     */
}

- (void)scrollToBottomDidPush:(UIBarButtonItem *)sender {
    [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:(kRowCount - 1) inSection:0]
                          atScrollPosition:UITableViewScrollPositionBottom
                                  animated:YES];
}

#pragma mark - TableView
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    return @"列表";
}

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

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return kRowCount;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *cellIdentifier = @"cellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
    }
    
    NSInteger row = indexPath.row;
    cell.textLabel.text = [_mArrDataSource[row] stringValue];
    
    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    
}

@end

AppDelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) UINavigationController *navigationController;

@end

AppDelegate.m

#import "AppDelegate.h"
#import "ViewController.h"

@interface AppDelegate ()
@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    ViewController *viewController = [[ViewController alloc] init];
    _navigationController = [[UINavigationController alloc] initWithRootViewController:viewController];
    _window.rootViewController = _navigationController;
    //[_window addSubview:_navigationController.view]; //当_window.rootViewController关联时，这一句可有可无
    [_window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application {
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
}

- (void)applicationWillTerminate:(UIApplication *)application {
}

@end