1.日期选择器（UIDatePicker）

日期选择器有四种模式
1.日期---年/月/日
2.日期时间---年/月/日/上下午/时/分
3.时间---上下午/时/分
4.倒计时定时器---时/分

显示效果

代码
#import "ViewController.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIDatePicker *datePicker;
@property (weak, nonatomic) IBOutlet UILabel *label;
- (IBAction)onlick:(UIButton *)sender;
@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
}
- (IBAction)onlick:(UIButton *)sender
{
    NSDate *theDate = self.datePicker.date;
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"YYYY-MM-dd HH:mm:ss";
    self.label.text = [dateFormatter stringFromDate:theDate];
}
@end

2.普通选择器（UIPickerView）

UIPickerView是UIDatePicker的父类
与UIDatePicker不同的是，UIPickerView需要两个非常重要的协议
1.UIPickViewDataSource
2.UIPickViewDelegate

显示效果

代码
#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.pickerView.dataSource = self;
    self.pickerView.delegate = self;
    
    NSBundle *bundle = [NSBundle mainBundle];
    NSString *plistPath = [bundle pathForResource:@"provinces_cities" ofType:@"plist"];
    //获取属性列表文件中的全部数据
    NSDictionary *dict = [[NSDictionary alloc] initWithContentsOfFile:plistPath];
    self.pickerData = dict;
    
    //获取省份名数据
    self.pickerProvincesData = [self.pickerData allKeys];
    //默认取出第一个省的所有市的数据
    NSString *selectedProvince = [self.pickerProvincesData objectAtIndex:0];
    self.pickerCitiesData = [self.pickerData objectForKey:selectedProvince];
}

- (IBAction)onclick:(UIButton *)sender
{
    NSInteger row1 = [self.pickerView selectedRowInComponent:0];
    NSInteger row2 = [self.pickerView selectedRowInComponent:1];
    NSString *selected1 = [self.pickerProvincesData objectAtIndex:row1];
    NSString *selected2 = [self.pickerCitiesData objectAtIndex:row2];
    NSString *title = [NSString stringWithFormat:@"%@,%@市", selected1, selected2];
    self.label.text = title;
}

#pragma mark - 实现UIPickViewDataSource方法
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 2;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    if (component == 0) //省份个数
    {
        return [self.pickerProvincesData count];
    }
    else    //市的个数
        return [self.pickerCitiesData count];
}

#pragma mark - 实现UIPickViewDelegate方法
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    if (component == 0) //显示省名
    {
        return [self.pickerProvincesData objectAtIndex:row];
    }
    else    //显示市名
        return [self.pickerCitiesData objectAtIndex:row];
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
    if (component == 0)
    {
        NSString *selectedProvince = [self.pickerProvincesData objectAtIndex:row];
        NSArray *array = [self.pickerData objectForKey:selectedProvince];
        self.pickerCitiesData = array;
        [self.pickerView reloadComponent:1];
    }
}

@end