137在搜索框中实现下拉列表效果（扩展知识：表格视图数据源为空数据时显示提示信息）

效果如下：

ViewController.h

#import <UIKit/UIKit.h>
#import "DropDownListViewController.h"

@interface ViewController : UITableViewController<UISearchBarDelegate, PassValueDelegate>
@property (strong, nonatomic) UISearchBar *searchBar;
@property (strong, nonatomic) NSMutableArray *mArrDataSourceOfTableView;
@property (strong, nonatomic) NSMutableArray *mArrDataSourceOfSearchBar;
@property (strong, nonatomic) DropDownListViewController *ddlViewController;
@property (strong, nonatomic) UILabel *lblEmptyDataMsg;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()
- (void)layoutUI;
- (void)loadData;
- (void)updateTableView:(NSString *)searchText;
- (void)setDDLHidden:(BOOL)isHidden animated:(BOOL)animated;
@end

@implementation ViewController
#define kRowCount 64

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

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

#pragma mark - Private Methods
- (void)layoutUI {
    [self loadData];
    
    self.navigationItem.title = @"在搜索框中实现下拉列表效果";
    
    _searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, self.tableView.frame.size.width, 50)];
    _searchBar.delegate = self;
    _searchBar.prompt = @"数字查询";
    _searchBar.placeholder = @"请输入0-63之间的数字";
    _searchBar.keyboardType = UIKeyboardTypeNumberPad;
    _searchBar.barStyle = UIBarStyleDefault;
    _searchBar.tintColor = [UIColor blackColor];
    [_searchBar sizeToFit]; //设置宽高大小自适应
    self.tableView.tableHeaderView = _searchBar;
    
    _ddlViewController = [[DropDownListViewController alloc] initWithStyle:UITableViewStylePlain];
    _ddlViewController.delegate = self;
    _ddlViewController.view.frame = CGRectMake(22.0, 68.0, 320.0, 0);
    [self.view addSubview:_ddlViewController.view];
    
    _lblEmptyDataMsg = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 50)];
    CGPoint newPoint = self.view.center;
    newPoint.y -= 25;
    _lblEmptyDataMsg.center = newPoint;
    _lblEmptyDataMsg.text = @"没有相关数据";
    _lblEmptyDataMsg.textColor = [UIColor grayColor];
    _lblEmptyDataMsg.textAlignment = NSTextAlignmentCenter;
    _lblEmptyDataMsg.font = [UIFont systemFontOfSize:20];
    _lblEmptyDataMsg.hidden = YES;
    [self.view addSubview:_lblEmptyDataMsg];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    [self setDDLHidden:YES animated:NO];
}

- (void)loadData {
    _mArrDataSourceOfTableView = [[NSMutableArray alloc] initWithCapacity:kRowCount];
    _mArrDataSourceOfSearchBar = [[NSMutableArray alloc] initWithCapacity:kRowCount];
    for (NSInteger i=0; i<kRowCount; i++) {
        [_mArrDataSourceOfTableView addObject:[NSString stringWithFormat:@"%ld", (long)i]];
        _mArrDataSourceOfSearchBar[i] = _mArrDataSourceOfTableView[i];
    }
}

- (void)updateTableView:(NSString *)searchText {
    [_mArrDataSourceOfSearchBar removeAllObjects];
    if (searchText.length == 0) {
        _mArrDataSourceOfSearchBar = [[NSMutableArray alloc] initWithArray:_mArrDataSourceOfTableView];
    } else {
        for (NSString *item in _mArrDataSourceOfTableView) {
            if ([item hasPrefix:searchText]) {
                [_mArrDataSourceOfSearchBar addObject:item];
            }
        }
    }
    //表格视图tableView更新
    [self.tableView reloadData];
    
    //设置当UITableView数据源为空数据时，显示提示信息标签_lblEmptyDataMsg
    _lblEmptyDataMsg.hidden = _mArrDataSourceOfSearchBar.count > 0;
}

- (void)setDDLHidden:(BOOL)isHidden animated:(BOOL)animated {
    NSInteger ddlHeight = isHidden ? 0 : 180;
    //声明并实现block代码块setHeightForDDL
    void (^setHeightForDDL)() = ^() {
        [_ddlViewController.view setFrame:CGRectMake(22.0, 68.0, 320.0, ddlHeight)];
    };
    
    if (animated) {
        //设置视图变化使用动画效果
        [UIView beginAnimations:nil context:nil];
        [UIView setAnimationDuration:0.3];
        setHeightForDDL();
        [UIView commitAnimations];
    } else {
        setHeightForDDL();
    }
    
}

#pragma mark - SearchBar
- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText {
    //必须设置为最顶层；否则在UITableView数据源为空数据后切换，会出现_ddlViewController.view不是最顶层的现象
    [self.view bringSubviewToFront:_ddlViewController.view];
    
    _ddlViewController.searchText = searchText;
    [self setDDLHidden:(searchText.length == 0) animated:YES];
    [_ddlViewController updateData];
    
}

- (void)searchBarSearchButtonClicked:(UISearchBar *)searchBar {
    //隐藏自定义的下拉列表视图
    [self setDDLHidden:YES animated:YES];
    
    [self updateTableView:searchBar.text];
    //隐藏键盘
    [_searchBar resignFirstResponder];
}

#pragma mark - TableView
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [_mArrDataSourceOfSearchBar count];
}

- (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];
    }
    cell.textLabel.text = _mArrDataSourceOfSearchBar[indexPath.row];
    return cell;
}

#pragma PassValueDelegate
- (void)passValue:(NSString *)value {
    if (value) {
        _searchBar.text = value;
        [self searchBarSearchButtonClicked:_searchBar];
    }
}

@end

PassValueDelegate.h

@protocol PassValueDelegate <NSObject>
- (void)passValue:(NSString *)value;

@end

DropDownListViewController.h

#import <UIKit/UIKit.h>
#import "PassValueDelegate.h"

@interface DropDownListViewController : UITableViewController
{
    @private
    NSString *_selectedText;
}
@property (strong, nonatomic) NSMutableArray *mArrResultList;
@property (copy, nonatomic) NSString *searchText;
@property (weak, nonatomic) id<PassValueDelegate> delegate;

- (void)updateData;

@end

DropDownListViewController.m

#import "DropDownListViewController.h"

@interface DropDownListViewController ()
- (void)layoutUI;
@end

@implementation DropDownListViewController
#define kRowCount 6
#define kHeightForRow 30.0

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

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

- (void)layoutUI {
    self.tableView.layer.borderColor = [UIColor blackColor].CGColor;
    self.tableView.layer.borderWidth = 1.0;
    
    _mArrResultList = [[NSMutableArray alloc] initWithCapacity:kRowCount];
    _searchText = nil;
    _selectedText = nil;
}

- (void)updateData {
    [_mArrResultList removeAllObjects];
    if (_searchText && _searchText.length > 0) {
        [_mArrResultList addObject:_searchText];
        for (NSInteger i=1; i<kRowCount; i++) {
            [_mArrResultList addObject:[NSString stringWithFormat:@"%@%ld", _searchText, (long)i]];
        }
    }
    
    [self.tableView reloadData];
}

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

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

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return (_searchText && _searchText.length > 0) ? kRowCount : 0;
}

- (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];
    }
    cell.textLabel.text = _mArrResultList[indexPath.row];
    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    _selectedText = _mArrResultList[indexPath.row];
    [_delegate passValue:_selectedText];
}

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

@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