<UIPickerViewDelegate,UIPickerViewDataSource>

其中数据源里面有两个必须实现的方法

//设置列数
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
    return count;
}

//设置指定列包含的项数
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{


}

UIPickerView是可以只设置单列的，列被称为component，此时返回的列数为1即可，单更多时候需要的是多列情况，此时设置返回值为自己所需要的列数即可。

在UIPickerViewDataSource数据源协议中，仅仅提供了UIPickerView包含几列以及每一列的项数，而每一行展示的选项是通过UIPickerViewDelegate协议中的方法来设置的。

//设置每个选项显示的内容
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
}
//获取用户当前选中的选项
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
   
}

UIPickerView基本属性和方法：

设置数据源对象以及代理对象

@property(nullable,nonatomic,weak) id<UIPickerViewDataSource> dataSource;                
@property(nullable,nonatomic,weak) id<UIPickerViewDelegate>   delegate;                  

重新加载列：

- (void)reloadAllComponents;
- (void)reloadComponent:(NSInteger)component;

获取当前选中的选项序号：

- (NSInteger)selectedRowInComponent:(NSInteger)component;

指定选中的项显示在中间位置，一般设置第一项放在中间：

- (void)selectRow:(NSInteger)row inComponent:(NSInteger)component animated:(BOOL)animated;

下面是一个简单的完整示例：

#import "ViewController.h"

@interface ViewController ()<UIPickerViewDelegate,UIPickerViewDataSource>
@property(nonatomic,strong)UIPickerView *pickerVIew;
@property(nonatomic,strong)NSDictionary *dictionary;
@property(nonatomic,strong)NSArray *provinceArray;
@property(nonatomic,copy)NSString *selectedProvince;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.dictionary = @{@"江苏":@[@"南京",@"徐州",@"镇江",@"无锡",@"常州"],@"河北":@[@"石家庄",@"保定",@"承德",@"沧州",@"秦皇岛"]};
    //获取字典中所有的省份并排序保存
    self.provinceArray = [[self.dictionary allKeys] sortedArrayUsingSelector:@selector(compare:)];
    self.selectedProvince = self.provinceArray[0];
    [self.view addSubview:self.pickerVIew];
    
}


//懒加载
- (UIPickerView *)pickerVIew{
    if (_pickerVIew == nil) {
        self.pickerVIew = [[UIPickerView alloc]initWithFrame:CGRectMake(0, 44, self.view.frame.size.width, 400)];
        _pickerVIew.layer.masksToBounds = YES;
        _pickerVIew.layer.borderWidth = 1;
        _pickerVIew.delegate = self;
        _pickerVIew.dataSource = self;
    }
    
    return _pickerVIew;
}


#pragma mark ------- dateSource&&Delegate --------

//设置列数
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
    return 2;
}

//设置指定列包含的项数
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{
    if (component == 0) {
        return self.provinceArray.count;
    }
    return [self.dictionary[self.selectedProvince] count];
}

//设置每个选项显示的内容
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
    if (component == 0) {
        return self.provinceArray[row];
    }
    return [self.dictionary[self.selectedProvince] objectAtIndex:row];
}

//用户进行选择
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
    if (component == 0) {
        self.selectedProvince = self.provinceArray[row];
        [self.pickerVIew reloadComponent:1];
        //设置第二列首选的始终是第一个
        [self.pickerVIew selectRow:0 inComponent:1 animated:YES];
    }
}



@end